Field study of office worker responses to fluorescent lighting of different CCT and lumen output

Accepted Manuscript

Field study of office worker responses to fluorescent lighting of different CCT andlumen output

Minchen Wei , Kevin W. Houser , PhD Brian Orland , Dean H. Lang , PhD NilamRam , PhD Martin J. Sliwinski , PhD Mallika Bose , PhD

PII: S0272-4944(14)00042-5

DOI: 10.1016/j.jenvp.2014.04.009

Reference: YJEVP 861

To appear in: Journal of Environmental Psychology

Received Date: 2 April 2013

Revised Date: 30 April 2014

Accepted Date: 30 April 2014

Please cite this article as: Wei, M., Houser, K.W., Orland, B., Lang, D.H., Ram, N., Sliwinski, M.J., Bose,M., Field study of office worker responses to fluorescent lighting of different CCT and lumen output,Journal of Environmental Psychology (2014), doi: 10.1016/j.jenvp.2014.04.009.

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http://dx.doi.org/10.1016/j.jenvp.2014.04.009

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FIELD STUDY OF OFFICE WORKER RESPONSES TO FLUORESCENT LIGHTING OF

DIFFERENT CCT AND LUMEN OUTPUT

Minchen Wei1, Kevin W. Houser1 PhD, Brian Orland2, Dean H. Lang2 PhD, Nilam Ram3 PhD,

Martin J. Sliwinski3 PhD, Mallika Bose2 PhD

1. Department of Architectural Engineering, The Pennsylvania State University, University Park,

PA

2. Department of Landscape Architecture, The Pennsylvania State University, University Park,

PA

3. Department of Human Development & Family Studies, The Pennsylvania State University,

University Park, PA

Author Information:

Minchen Wei

The Pennsylvania State University

Dept. of Architectural Engineering Phone: +1-(814) 863-3555

104 Engineering Unit A Fax: +1-(814) 863-4789

University Park, PA 16802 < Email: [email protected]

Kevin W. Houser


Dept. of Architectural Engineering Phone: +1-(814) 863-3555

104 Engineering Unit A Fax: +1-(814) 863-4789

University Park, PA 16802 < Email: [email protected]

Brian Orland


Department of Landscape Architecture Phone: +1-(814)-865-6315

121 Stuckeman Family Building

University Park, PA 16802 Email: [email protected]

Dean H. Lang

The Pennsylvania State University Phone: +1-(814)-865-5732



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Nilam Ram


0422 Biobehavior Health Building


Martin J. Sliwinski


0422 Biobehavior Health Building


Mallika Bose




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Field study of office worker responses to fluorescent lighting of different CCT and lumen output

Highlights:

• Smart phones collected ecological momentary assessments of occupant responses.

• Participants responded more strongly to changes in CCT than changes in lumen output.

• Conditions at 5000 K were rated to be too cool.

• Conditions at 5000 K were rated to provide less visual comfort than 3500 K.

• Results are incompatible with DOE’s spectrally enhanced lighting (SEL) method.

Abstract

A field study was performed to examine the effects of correlated color temperature (CCT) and lumen

output of fluorescent lighting on office occupants’ visual comfort, brightness perception, satisfaction,

and self-reported productivity. Twenty-six participants were recruited (mean age = 38.8 years; age

range = 23 to 55 years). Ten of them had daylight access in their personal work areas. Four lamp types

were selected to create luminous conditions organized as a 2 × 2 factorial design, comprising two levels

of CCT (i.e., 3500 and 5000 K) and lumen output (i.e., 2330 and ≈ 3000 lm). Each condition lasted two

weeks. Under each condition, participants adapted during the first week. During the second week they

completed ecological momentary assessments (EMAs) three times daily using smart phones. Two of the

daily EMAs included questions about lighting. Participants also completed a web-based survey on the

last day of each condition. The results from the EMA (60.0% response rate) and web-based (77.2%

response rate) surveys were generally consistent, indicating that CCT significantly affected spatial

brightness perception, visual comfort, satisfaction, and self-reported productivity. The luminous

conditions at 5000 K (visually cooler) were rated to be brighter than those at 3500 K (visually warmer),

especially when higher lumen output was in place. However, the increase in spatial brightness

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perception came with lower satisfaction, worse visual comfort, and worse self-reported productivity.

The conditions at 5000 K were judged to be too cool, especially for those who had daylight in their

work areas. The results of this study do not support the spectrally enhanced lighting (SEL) method

advocated by the U.S. Department of Energy (DOE) as an energy savings strategy. Even when higher

CCT resulted in higher spatial brightness perception, occupants’ visual comfort and satisfaction were

compromised.

Keywords: fluorescent lamp, correlated color temperature (CCT), lumen output, visual comfort,

perception, brightness, satisfaction, self-reported productivity

1. Introduction

In 2010, about 41% of primary energy was consumed by residential and commercial buildings in the

United States and lighting accounted for about 10% of the total (DOE, 2012). With the development of

lighting technologies and growth of knowledge about human’s perceptions that are stimulated by

optical radiation, there is potential to save energy by better aligning the optical radiation of electric

light sources with the needs of human vision and perception (Houser, Tiller, and Hu, 2004; Houser,

Fotios, and Royer, 2009; Royer and Houser, 2012; Wei and Houser, 2012).

In an effort to reduce the energy consumed by lighting systems in commercial buildings, the U.S.

Department of Energy (DOE) is advocating adoption of “spectrally enhanced lighting” (SEL), the central

tenet being that correlated color temperature (CCT) and illuminance can be traded to maintain equal

spatial brightness perception and visual acuity. According to the SEL method, using higher CCT lamps

with lower lumen output (which is directly related to wattage) will maintain equivalent brightness

perception and visual acuity in comparison to using lower CCT lamps with higher lumen output. DOE

claims that this method, which essentially redefines the meaning of “light”, can reduce lighting energy

consumption in commercial buildings by 20 to 40% (DOE, 2013b; PNNL, 2006).

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The SEL method is rooted in the relationship between the ratio of the scotopic to photopic lumens (S/P)

of a stimulus and resulting spatial brightness provided by the stimulus (DOE, 2013a; PNNL, 2006). It

claims that perception of spatial brightness is positively correlated to the S/P ratio of the stimulus

(DOE, 2013a)—the belief is that lamps with higher S/P ratio can provide higher spatial brightness

with the same photopic quantities (e.g., illuminance, luminous flux, luminance). If true, using a lamp

with a higher S/P ratio will allow photopic quantities to be reduced (concomitant with lighting energy

use), while maintaining comparable spatial brightness perceptions. In 2013, the Illuminating

Engineering Society (IES) released TM-24-13 titled “An optional method for adjusting the

recommended illuminance for visually demanding tasks within IES illuminance categories P through Y

based on light source spectrum” (IES, 2013; Houser, 2014a). IES illuminance categories P through Y

are from the 10th edition IES Lighting Handbook and span a range of 300 to 10,000 lx for occupants

from 25 to 65 years of age (DiLaura, Harrold, Houser, Mistrick, and Steffy, 2011; DiLaura, Houser,

Mistrick, and Steffy, 2011; Houser, 2014b). TM-24-13 introduced the Equivalent Visual Efficiency

(EVE) calculation method. The EVE calculation permits designers to optionally employ lamps of higher

S/P ratio and lower illuminance to maintain visual efficiency. TM-24-13 suggests that such a tradeoff

is benign—that is, the increase in CCT and decrease in illuminance will not negatively affect

brightness perceptions or visual comfort.

When considering illumination in commercial buildings, the S/P ratio is sometimes simplified to CCT

(for computational details of CCT see: Ohno, 2014). Lamps with higher S/P ratios also tend to have

higher CCTs (New Buildings Institute, 2013; Steffy, 2008; Ju, Chen and Lin, 2012). The New Buildings

Institute has stated that 4100 K lamps will appear brighter than 3000 or 3500 K lamps (New Buildings

Institute, 20013). Steffy has suggested that spaces lighted with lamps below 3500 K may appear

dimmer to some users, assuming illuminance is constant (Steffy, 2008). Despite the popular wisdom

that increasing CCT is associated with increased brightness perception, many scientific studies have

not found support for the S/P theory or the employment of higher CCT lamps to improve spatial

brightness (Boyce, 1977; Boyce and Cuttle, 1990; Boyce, Akashi, Hunter, and Bullough, 2003; Dikel

EE, Burns GJ, Veitch JA, Mancini S, and Newsham GR, 2014; Houser and Hu, 2004; Hu, Houser and

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Tiller, 2006; Houser et al. 2004, 2009; Fotios, 2011; Royer and Houser, 2012; Wei, 2011). Even if the

effects of CCT, S/P ratio, or the SEL method on visual acuity and spatial brightness are valid, spatial

brightness and visual acuity are not the only determinants of occupant satisfaction with a lighting

system (DiLaura et al. 2011; Fotios, 2011).

The present field study was designed to examine the practicality of the SEL method for lumen output

reduction, and thus energy reduction, in a typical office building. The experimental design expanded

the methodologies of past studies by using smart phones to collect occupants’ responses (ecological

momentary assessments (EMAs)), in addition to web-based surveys. The typical previous lighting field

studies used paper-based or web-based surveys to collect responses from occupants at the end of the

study (PNNL, 2006), which were types of pre-post measures. The pre-post method of data collection is

limited by recall bias and is not well suited to address how behavior or experience changes over time

and across contexts. EMA is a collection of methods for obtaining repeated real-time data on

participants’ behavior and experience in their natural environments (Shiffman, Stone, and Hufford,

2008), with the term coined in 1994 (Stone and Shiffman, 1994). EMA can minimize recall bias,

improve ecological validity, and document variation over time (Shiffman et al. 2008). EMA methods are

being used in a wide range of disciplines, such as clinical psychology and health psychology (Bolger

and Laurenceau, 2013). To our knowledge, EMA method was only employed in one lighting study

(Smolders, de Kort, and van den Berg, 2013). In this study, we also considered occupants’ visual

comfort, overall satisfaction, satisfaction with color temperature, contrast, self-reported productivity,

together with spatial brightness perception. All of these are key components to evaluate a lighting

system and its effect on occupants (Newsham et al. 2009; PNNL, 2006).

This paper is an extension of the work originally presented in the 2013 Architectural Engineering

Institute Conference (Wei et al., 2013) and provides more comprehensive analyses and results.

2. Methods

The experimental design—including informed consent, recruitment procedures, and experimental

protocols—were approved by Penn State’s Institutional Review Board (IRB).

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2.1. Setting

This field study took place in a four-story office building in Central Pennsylvania. The lighting was

manipulated in multiple areas—open-plan areas, cubicles, private offices, common areas, and

conference rooms—which comprise the spaces where the occupants spent most of their working hours.

The general lighting in these areas was provided by 2 ft × 4 ft recessed troffers or indirect pendant

luminaires. Each luminaire featured two 32 W, 3000 or 3500 K, T8 linear fluorescent lamps with a

color rendering index (CRI) of 85 and mean lumen output of 2945 lm. Some occupants also had

supplementary under-cabinet task lights and table lamps, as well as occupancy sensors, shades, and

blinds. Figures 1 and 2 illustrate examples of the private offices, an open-plan area, and some of the

luminaires. The linear fluorescent lamps in all of the hard-wired luminaires— including recessed

troffers, pendant luminaires, and under-cabinet task-lights—were changed multiple times over the

course of the study.

2.2. Participants

All individuals working in the space were approached, via e-mail, telephone, or in person, to

participate in the study by providing on-going reports of their perceptions of the lighting and work

environment. No exclusion criteria were used to screen participants. Twenty-six participants (11 male,

15 female, Mean age = 38.8, SD = 10.01, range 23 to 55 years) completed the 3 month protocol.

Twenty-four identified as White, with the remaining 2 identifying as Black or African American. None

of the participants reported abnormal color vision and none had knowledge about the lamps that were

employed in the study. All the participants had worked in their workspace for more than four months.

Eight participants had private office; the other 18 had work stations in open areas. Ten participants

had daylight access in their personal work areas, by which we mean that they were in close proximity

to a window. The other 16 worked in interior spaces without visual access to a window. The sample is

representative of this particular office building, and is believed to be representative of a typical

commercial office settings in the US.

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2.3. Procedure and Surveys

The study lasted about three months from October 2011 to January 2012, which included the

Thanksgiving and Christmas holidays, during which times the building was closed. Four luminous

conditions were created to test DOE’s SEL method, as later discussed in detail.

The participants reported their daily experiences in the baseline condition (i.e., the existing condition

in the building as described in Section 2.1), four treatment conditions, and again in the baseline

condition. Each condition lasted two weeks. All the fluorescent lamps were replaced every other

Saturday without notifying the occupants. The entire work environment had uniform light source color,

thus allowing the occupants to be completely adapted to the luminous environment. In the first week

of each treatment, the participants adapted to the luminous environment; in the second week, they

were asked to complete the EMAs three times daily when prompted (i.e., in the morning before work,

at lunch time, and at the end of work) using a smart phone, which was kept by each participant

during the study. Additionally, a set of web-based surveys were completed by the participants prior to

the start of the treatment conditions (i.e., baseline), on the last day of each treatment condition, and

after returning to the baseline condition.

2.4. Variables

2.4.1. Independent Variables

Four treatment conditions were created and provided by four types of commercially available linear

fluorescent lamps (purchased through normal channels), organized as a 2 × 2 factorial design, with

two levels of CCT (i.e., 3500 and 5000 K) and lumen output (i.e., 2300 and ≈ 3000 lm) as shown in

Table 1. Figure 3 shows the spectral power distribution (SPD) of each lamp type, as measured in a lab

space with walls painted with Munsell N8 spectrally neutral paint.

In addition to CCT and lumen output, the daylight accessibility through a window was also regarded

as an additional factor that could affect the dependent variables.

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All four lamp types were purposely selected—and especially lamp pair C and D—to test the DOE SEL

method. According the SEL method, lamp types C and D should provide equal spatial brightness

perception, as discussed in Section 4.

2.4.2. Dependent Variables

The EMAs and web-based surveys covered different aspects: background information, information

about work area, lighting beliefs, satisfaction with the indoor-environmental conditions (e.g., lighting,

air quality, noise, privacy, thermal comfort), health and wellbeing, mood, controls behavior, and self-

reported productivity. Copies of the surveys are available upon request. This paper mainly focuses on

the questions related to lighting. The terms related to lighting that were used in the surveys, such as

color temperature, were explained within the surveys in an effort to minimize misunderstanding.

Some responses provided by the participants were regarded as unreliable data (e.g., the participants

did not use the overhead luminaires during that week, the participant was out of office in the

morning/afternoon, or the participant completed the lunch-time and the end-of-work EMAs at the

same time). These cases were discarded from the analyses. The most common reason for discarding

data was because the participant was absent from his or her office.

2.4.2.1. Ecological Momentary Assessments (EMAs)

Three semantic differential-scaled questions were included in two EMAs—at lunch time and at the end

of work—regarding the perception and satisfaction of the luminous environment. Responses to the

three questions, each answered on slider-type interface and coded on a 0-100 scale, are shown in

Table 2. A total of 1040 responses were expected to be collected for these three questions throughout

the study; 415 of them were missing or regarded as unreliable as described above. The missing and

unreliable data were randomly distributed.

2.4.2.2. Web-based Surveys

There were 15 questions related to lighting in the web-based surveys, as listed in Table 3, which can

be divided into six categories: visual comfort, overall satisfaction, quantity (brightness), color

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temperature, productivity, and contrast. Most questions were rated on a seven-point Likert scale (1-7),

with higher values indicating stronger agreement with the statement and 4 indicating neutral; two

questions employing different rating scales are noted in Table 3. These questions were either used

verbatim or adapted from previous studies (CBE, 2013; HOPE, 2013; Veitch, Farley, and Newsham,

2002). A total of 1560 responses were expected to be collected; 356 of them were missing data or

regarded as unreliable. The missing and unreliable data were randomly distributed.

2.4.2.3. Lighting Beliefs

Twenty-four lighting belief questions were included in the first and last web-based surveys, as listed in

Table 4. All of these questions were rated on a seven-point Likert scale (1-7), with higher values

indicating stronger agreement and 4 indicating neutral. The questions were from a previous study

(Veitch & Gifford, 1996).

2.5. Illuminance Measurements

Illuminance measurements were taken on desktop surfaces in three private offices under each

treatment using a Minolta T-10 illuminance meter (a NIST traceable calibration certificate is on file).

The measurements were taken at approximately the same locations, as indicated in Figures 1 (a)-(c). In

Office A and B, two illuminance measurements were taken: that provided by daylight only, and that

provided by the overhead luminaires and daylight. The illuminance provided by just the overhead

luminaires was taken as the difference between these two measurements. In Office C, the illuminance

provided by the overhead luminaires only was measured directly since there was no daylight access.

Table 5 summarizes the means and standard deviations in the three offices under the four treatment

conditions. It can be observed that for each of the three offices, the mean illuminances provided by the

overhead luminaires only under the four luminous conditions have a similar trend in comparison to

the lumen output of the lamp types.

3. Results

Tables 2 and 3 summarize the mean ratings with standard deviations given by the participants, and

the number of responses during each treatment condition in the EMAs and web-based surveys.

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Figures 4(a) – (c) show the mean ratings with 95% confidence intervals for the EMAs during the four

treatment periods.

As the data collected from the participants were nested, multilevel models were employed to analyze

the effect of the independent variables on the dependent variables by including all the raw reliable

responses (i.e., the responses from the same participants under same luminous condition were not

averaged). Table 6 summarizes the results of these mixed-models.

3.1. Visual Comfort

The participants were asked to evaluate the visual comfort under each treatment condition by

responding to two questions. One question was part of the EMAs (EMA1) and the other was part of the

web-based surveys (Web1). The results of both questions indicate that CCT, the two-way interactions

between daylight accessibility and CCT, and between CCT and lumen output, were significant factors.

Similar patterns and results were obtained from the two questions, as shown in Figure 5 (a). In the

mixed-model for EMA1, the three-way interaction was also significant.

As shown in Figure 5, the conditions at 5000 K were rated to be less comfortable than those at 3500 K,

especially when the 5000 K was combined with 3000 lm. For those who had daylight access in their

office, the conditions provided by 5000 K were rated to have lower visual comfort than those provided

by 3500 K; for those who did not have daylight access, the four conditions provided similar visual

comfort.

3.2. Overall Satisfaction

Three questions regarding overall satisfaction were included in the web-based surveys: Web2 – Web4.

Significant correlations were found among them; Spearman’s rho and Pearson correlation coefficients

ranged from 0.76 to 0.88. The main effect of CCT, the two-way interaction between CCT and lumen

output, and between CCT and daylight accessibility were significant or nearly so, as shown in Table 6.

As shown in Figure 6, the participants had lower overall satisfaction under the conditions at 5000 K,

especially when it was combined with higher lumen output. For those with daylight access, the

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difference between the conditions at two CCTs was larger than that for those who did not have daylight

access. It can be observed that patterns shown in Figure 6 were similar to those shown in Figure 5.

3.3. Quantity

To evaluate the effect of luminous conditions on brightness perception, one question was included in

the EMAs (EMA2) and three were included in the web-based surveys (Web5 – Web7).

Web5 and Web6 asked whether the light level was sufficient to read materials on the desk and for

computer work, respectively. None of the independent variables or interactions was significant, as

shown in Table 6. All the ratings provided by participants under treatment conditions for Web5 and

Web6 were above 5.0 (the rating for “agree”), indicating that all the treatment conditions were able to

provide enough horizontal and vertical light level for the participants to read the materials on the desk

and to use the computer monitor. However, this does not necessarily mean that the light levels were

appropriate for the participants.

EMA2 asked the participant if the light level was appropriate. Web7 asked whether he or she was

satisfied with the brightness. The linear mixed-models for EMA2 and Web7 revealed that CCT, lumen

output, and the two-way interaction between them were significant or nearly so. In addition, the two-

way interaction between daylight accessibility and lumen output was another significant factor for

Web7.

As shown in Figures 7 and 8, the luminous conditions at 5000 K were rated to be brighter than those

at 3500 K; the conditions provided by the lamps with 3000 lumens were rated to be brighter than

those with 2330 lumens. The existence of a statistical interaction between CCT and lumen output is

more important, showing that the participants thought the luminous environment provided by lamp

type B (5000 K with 3000 lm) was too bright. In contrast, the other three conditions were rated near

the rating of “just right” in both EMAs and web-based surveys, which were significantly different from

lamp type B. These results are consistent to those found in Web5 and Web6.

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3.4. Correlated Color Temperature (CCT)

Three questions in the web-based surveys (Web8 – Web10) and one question in the EMAs (EMA3) were

related to satisfaction with CCT.

For both EMA3 and Web8, the main effect of CCT and the two-way interaction between CCT and

lumen output were significant factors. The two-way interaction between daylight accessibility and CCT

was also significant for EMA3. For EMA3, the rating scale was “too cool” – “too warm”; for Web8, the

higher the rating, the more satisfied with the color temperature. As shown in Figures 9 and 10, the

conditions with 5000 K were evaluated to be too cool and had lower rating of satisfaction than those

with 3500 K, especially when it was combined with higher lumen output. Figure 9 also shows that for

those who had access to daylight, the conditions with 5000 K were especially judged to be too cool.

For Web9 (prefer CCT to be warmer) and Web10 (prefer CCT to be cooler), a significant negative

correlation was found (Pearson correlation coefficient = -0.80; Spearman’s rho = -0.78). The significant

factors for Web9 were the main effect of CCT and the two-way interactions between access to daylight

and CCT, and CCT and lumen output. CCT was the only significant factor for Web10. As observed

from Figure 11 and Table 3, under the conditions at 5000 K, the participants would have preferred the

color temperature of the electric lighting to be warmer (Web9), and would not have preferred the color

temperature of the electric lighting to be cooler (Web10).These opinions were especially forceful when

the higher lumen output lamps were in place. For the conditions with 3500 K, the attitudes towards

color temperature were close to neutral for both Web9 and Web10.

3.5. Self-reported Productivity

Two questions included in the web-based surveys, Web11 and Web12, were related to the effect of

lighting conditions on self-reported productivity. Responses are summarized in Table 3. Web11 was

rated on a seven-point Likert scale; Web13 was rated from -20% to +20% (i.e., participants were asked

to choose how the lighting conditions had increased or decreased their productivity from 0%, 5%, 10%

or 20%). When performing the analyses, the choices of percentage were converted to a seven-point

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scale, with 4 indicating 0% (i.e. no change), 1 to 3 indicating -20%, -10%, and -5%, and 5 to 7

indicating +5%, +10%, and +20%, as noted in Table 3.

CCT and the interaction between CCT and daylight accessibility were significant factors for these two

questions. The interaction between CCT and lumen output was another significant factor for Web11.

On average, participants did not report that the conditions at 3500 K had a negative effect on their

productivity. The conditions at 5000 K tended to decrease self-reported productivity with higher

ratings for Web11 and lower ratings for Web12, especially for those who had daylight access in their

offices. When 5000 K was combined with 3000 lm, it had the most negative effect on self-reported

productivity.

3.6. Computer Screen Contrast and Glare

Web13 and Web14 were included in the web-based surveys to assess computer screen contrast. One

question, Web15, was included in the web-based surveys to assess glare on the computer screens. For

Web13 and Web14, no significant factors were found; for Web15, both CCT and lumen output were

significant factors.

As shown in Figure 14, though the conditions at 5000 K and the conditions at 3000 lm were rated to

have higher glare from the computer screen, the ratings were around or below neutral, indicating that

the amount of light reflected from monitors was acceptable under all conditions.

3.7. Comparisons of Lamp Pairs

Three lamp pairs were of particular interest in evaluating the reasonableness of the SEL method: C

versus D, A versus D, and B versus C. According to the SEL method, lamp type D and B should

provide higher spatial brightness and visual acuity than lamp type A and C, respectively; lamp type C

and D should provide the same spatial brightness and visual acuity. Comparisons of these three pairs

were made for all questions in EMAs and web-based surveys, as listed in Table 6.

Lamp type C and D yielded similar spatial brightness perceptions, as would be predicted by the SEL

method. However, this was achieved at the expense of visual comfort, overall satisfaction, and

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satisfaction with color temperature. The participants’ responses indicated that the correlated color

temperature under the illumination of lamp type D was too cool.

For lamp pair B and C—two lamps with the same lumen output (≈ 3000 lm) but different CCTs (5000

K for B and 3500 K for C)—the condition at 5000 K was perceived to be brighter than the condition at

3500 K. However, the higher CCT lighting provided lower visual comfort, lower overall satisfaction, less

satisfaction of color temperature, and a reduction in self-reported productivity.

Lamp pair A and D had the same lumen output, but D had higher CCT. If the SEL method was valid,

the condition under lamp type D should have been perceived to be brighter than that under A. The

results in Table 6 indicate that these two lamp types yielded similar perceptions of spatial brightness.

Furthermore, the condition under lamp type D was rated to have lower overall satisfaction and it was

perceived to be too cool.

3.8. Lighting Belief

Twenty-four lighting belief questions were included in the first and last web-based surveys. They were

answered by all the participants, as summarized in Table 4. These questions were originally developed

and deployed by Veitch and Gifford (1996).

The attitudes on three questions (i.e., LB9, LB23, LB24) changed significantly after the study, as

summarized in Table 4 (paired sample t-tests and Wilcoxon signed-rank tests yielded the same

statistical conclusions).

The most significant change can be observed on LB24 “If the light is visually cool, my office

environment feels uncomfortable”. The attitude towards cool light changed after the study, which was

consistent with the results in the EMAs and web-based surveys. Specifically, on average, participants

were unhappy with the 5000 K lighting conditions. The responses to LB9 also corroborate the survey

results: when the luminous conditions were rated to be too bright, visual comfort was also rated to be

low. The reason for the significance of LB23 is not clear.

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4. Discussion

This study was designed to investigate participants’ responses between lighting of different CCTs by

looking at within-subject differences. As a field study, it was impractical to counterbalance the order of

the four lamp types in order to avoid potential order bias. The participants completed the web-based

surveys twice under the baseline condition, with one prior to and one after the four treatment

conditions (as described in Section 2.3), which allowed us to test for an order effect. Both paired

sample t-tests and Wilcoxon signed rank tests were employed to test the difference between these two

surveys. Only one question (Web9) had a significant difference between these two surveys, where the

mean responses were 4.36 and 3.64, which are both near the neutral point of 4.0. These results

suggest that there was not a significant bias caused by the order of the luminous conditions.

Lamp types C and D were specifically chosen to test DOE’s SEL method and the effect of the S/P ratio

on spatial brightness. Two measures, (S/P)0.5 and (S/P)0.78, have been suggested as correlates for

spatial brightness (Berman, Jewett, Fein, Saika, and Ashford, 1990; DOE, 2013b) . The (S/P)0.5 and

(S/P)0.78 ratio of lamp type C to D is 0.87 and 0.79 respectively. If (S/P)0.78 was able to predict spatial

brightness, the treatment conditions provided by lamp type C and D should have been perceived as

equally bright, as the lumen output ratio of lamp type D to C is 0.78. No significant difference in

brightness perception was observed between the conditions provided by lamp type C and D, in EMA2

and Web7, as shown in Tables 2 and 3. The (S/P)0.78 model accurately predicted spatial brightness

perception for this lamp pair. However, this should not be generalized to mean that all lamps with

higher CCT or higher S/P ratio will always appear brighter (see, for example: Dikel et al., 2014; Hu et

al., 2006; Houser et al., 2009). Lamps A and D were rated as providing similar spatial brightness, even

though lamp type D had higher CCT than A. In this instance, the SEL method failed to accurately

predict spatial brightness perception. As pointed out by Houser et al. (2009) and Royer and Houser

(2012), the initial argument made by Berman and his colleagues on the correlation between S/P ratio

and spatial brightness was based on metameric stimuli, which have the same chromaticity coordinates

(Berman et al., 1990). The results from the Berman et al. (1990) study cannot be generalized to all

stimuli since metamerism no long exists when stimuli with different CCTs are compared. The DOE’s

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SEL method, which encourages the use of lamps with higher CCT, is based on a generalized concept

that treats CCT and illuminance as tradable lighting characteristics with comparable effects on

brightness perception and visual acuity—despite laboratory studies to the contrary. It has been argued

that both CCT and the S/P ratio are inadequate predictors of spatial brightness perception because

they oversimplify an illuminant’s SPD (Houser et al., 2004, 2009; Hu et al., 2006; Royer and Houser,

2012). This study provides further evidence that the S/P ratio is unable to predict spatial brightness

perception in a way that can be generalized to practical contexts.

All other studies that we know of that have investigated DOE’s SEL method have employed just one

pair of lamp types—for example, like those comparable to lamp pair C and D in our study (i.e. one

lamp type having higher CCT and lower lumen output; the other having lower CCT and higher lumen

output) (Veitch and Gifford, 1996; Houser and Hu, 2004; CBE, 2013; DOE, 2013c). If only brightness

perception for the lamp pair of C and D were to be considered, while ignoring all other lamp pairs and

psychophysical evidence, then it would be possible to incorrectly conclude that these results are

compatible with DOE’s SEL method. To our knowledge, no previous field study about the DOE’s SEL

method employed a full-factorial design. Thus, those studies were less likely to observe the failure of

the SEL method. Furthermore, some previous studies increased the color rendering index (CRI) at the

same time that they were increasing CCT (DOE, 2013c), thus confounding CRI with CCT. All four lamp

types in our study had similar values of CRI (82 or 85).

The strong reactions to CCT in this study merit further consideration. As shown in Table 6, CCT was

found to significantly contribute to evaluations of visual comfort, overall satisfaction, self-reported

productivity, contrast and glare, and color temperature. Generally speaking, occupants tended to give

lower ratings for visual comfort and overall satisfaction to the conditions at 5000 K, than to conditions

at 3500 K, especially when combined with higher lumen output or when daylight was accessible.

Participants rated the conditions at 5000 K as too cool and self-reported productivity was lower under

these conditions. For the two lamp pairs that provided similar spatial brightness (i.e. lamp pair A and

D, lamp pair C and D), the conditions at higher CCT were always rated to be less comfortable and the

occupants evaluated the color temperature as too cool.

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If the SEL method or IES TM-24-13 were to be true, then lamp type D should have received more

favorable ratings than lamp type C, since the higher S/P ratio provided by lamp D allows lower

illuminance levels with equal spatial brightness (DOE, 2013a) and visual acuity (DOE, 2013a; IES,

2013). Even if the SEL method were to appropriately characterize spatial brightness and visual acuity

for lamp pair C and D, the energy reduction would be achieved at the expense of visual comfort,

satisfaction with the luminous environment, and self-reported productivity. It should be clear that

brightness and visual acuity are not the only consideration when evaluating the luminous

environment. Other work suggests that the effect of SPD on the appearance of human complexions

and objects is a key aspect of lighting quality (Sanders, 1959; Schanda, 1985; Quellman and Boyce,

2002; Wei, Houser, Allen, and Beers, 2014; Houser, Wei, David, and Krames, 2014). If higher CCT

lighting yields unacceptable appearance of skin tones, negative effects on mood, motivation, and work

performance should be expected for some occupants.

Daylight can provide a range of benefits, including improvement of occupant satisfaction and

productivity, enhancement of circadian rhythms, and energy savings (when daylight dimming is

employed) (DiLaura, Houser, Mistrick, and Steffy, 2011). The color temperature of daylight ranges from

5300 K for an overcast sky to above 6000 K for a clear sky (Begemann, Van den Beld, and Tenner,

1997; Hernández-Andrés, Lee, and Romero, 1999). ASHRAE noted that sources of 4100 or 5000 K will

match daylight more closely than 3500 K sources (ASHRAE, 2011). Yet, in this study—though the

conditions at 5000 K were closer to the color temperature of daylight—the occupants who had daylight

access in their work area felt uncomfortable working under the 5000 K conditions. They rated the

color temperature as being too cool and believed that the lighting had a negative effect on self-reported

productivity, especially when the higher lumen output was in place, as shown in Figures 5, 6, 9 and

12. Why this occurred merits further investigation. For the comparison between lamp type C and D,

direct access to a window did not affect any question in the EMAs or web-based surveys, which is

consistent with the result in another field study (PNNL, 2006).

The results from the EMAs and the web-based surveys were generally consistent with each other,

though there were some variations. The participants completed EMAs 10 times, but only completed

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the web-based surveys once under each treatment condition. The EMAs were conducted via smart

phones, which were collecting real-time feedback from the participants. With the larger number of

responses and the collection of real-time feedback, we believe that the EMAs have higher reliability

than the web-based surveys. Our EMAs were rooted in real-time observations, whereas the web-based

surveys were reliant upon memory. Nevertheless, the overall consistency between the two surveys is

one indicator of the reliability of the results.

5. Conclusions

In this field study, the effect of four luminous conditions on occupants’ visual comfort, overall

satisfaction, brightness perception, satisfaction with color temperature, self-reported productivity, and

contrast were tested, organized as a 2 × 2 factorial design, comprising two levels of CCT (i.e., 3500 and

5000 K) and lumen output (i.e., 2330 and ≈ 3000 lm). Twenty-six participants were recruited. The

mean age was 38.8 years with a range of 23 to 55 years and a standard deviation of 10.01. Ten of

them had daylight access in their personal work areas. Two types of surveys—EMAs that gathered

brief but frequent assessments, and web-based surveys that were less frequent but contained many

more questions—were employed to evaluate occupants’ responses to the luminous conditions. Results

from the in situ EMAs and the retrospective web-based surveys were relatively consistent. From these

surveys, we conclude:

• For spatial brightness perception, all four conditions were rated to be adequate.. When higher

CCT was combined with higher lumen output, participants, on average rated the lighting as too

bright.

• The conditions at 5000 K or at higher lumen output were evaluated to have more reflected light

or glare in the computer screen, but to a degree that was still acceptable to the participants.

• For overall satisfaction or visual comfort, the conditions at 5000 K were regarded as less

comfortable than those at 3500 K. The 5000 K conditions were rated to be too cool and the

3500 K lamps were rated as just right on a scale of warm to cool. These responses were

especially pronounced for the higher lumen output lamps. For participants that had daylight

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access, 5000 K was especially judged to be too cool and uncomfortable. Self-reported

productivity and work performance were negatively affected under these conditions, as

evaluated by the participants. Preference for a warmer color temperature was expressed by the

participants when under 5000 K lighting.

• A full-factorial experiment was designed to test the DOE SEL method. The lamp type with

higher CCT were sometime judged to provide comparable spatial brightness as the ones with

lower CCT, which, in isolation, may appear to be consistent with the DOE SEL method..

However, for two lamp pairs with equal lumen output, the lamp with higher CCT failed to

provide higher spatial brightness, which represents a failure of the DOE SEL method.

• For the higher CCT conditions, participants gave lower ratings for visual comfort, overall

satisfaction, and satisfaction with color temperature. The higher CCT conditions were also

perceived to be too cool, especially for occupants with access to daylight.

Though the energy saving potential of the DOE SEL method is appealing because of its simplicity, our

data suggest that it cannot be generalized and applied to building interiors. Even for the limited

conditions where the DOE SEL method appropriately characterized spatial brightness perception,

visual comfort, overall satisfaction, and self-reported productivity were all sacrificed.

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Figures

(a) (b)

(c)

Figure 1 Photograph of three private offices (Office A, Office B, and Office C). The mean illuminances, as shown in Table

5 were calculated from the measurements taken around the locations labeled in the photographs.

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Figure 2 Photograph of an open-plan area showing 2 ft × 4 ft recessed luminaires.

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(a)

(b)

Figure 3 Relative spectral power distribution (SPD) of the lamp types used in the four treatment conditions. These

measurements were taken by a spectroradiometer in a lab space with walls painted with Munsell N8 spectrally neutral

paint, accounting for interreflections with the luminaire and from room surfaces. (a) SPD of lamps A and D; (b) SPD of

lamps B and C.

0%

20%

40%

60%

80%

100%

380 430 480 530 580 630 680 730 780

Relative Output

Wavelength (nm)

A: 2330 lm 3500 K

D: 2330 lm 5000 K

0%

20%

40%

60%

80%

100%

380 430 480 530 580 630 680 730 780

Relative Output

Wavelength (nm)

B: 2935 lm 5000 K

C: 3000 lm 3500 K

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(a) (b)

(c)

Figure 4 The mean ratings with standard deviations given by participants for the EMAs on each day during the four

treatment periods; the lunch-time survey and end-of-work survey were combined. The participants experienced each

treatment for two weeks (10 weekdays), but only completed these EMAs in the second week (5 weekdays). (a) EMA1 –

“how satisfied were you with the visual comfort of the electric?”; (b) EMA2 – “how bright was the lighting in your work

area?”; (c) EMA3 – “the color temperature of the electric lighting in your work area was:” (Wei et al., 2013).

0

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Rat

ing

Day

3500 K 5000 K 3500 K 5000 K2330 lm 3000 lm 3000 lm 2300 lm

VerySatisfactory

VeryUnatisfactory 0

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Rat

ing

Day

3500 K 5000 K 3500 K 5000 K2330 lm 3000 lm 3000 lm 2300 lm

Too Bright

Too Dim

0

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Rat

ing

Day

3500 K 5000 K 3500 K 5000 K2330 lm 3000 lm 3000 lm 2300 lm

Too Cool

Too Warm

With daylight access

Without daylight access

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(a)

(b)

Figure 5 The significant factors and interactions plots in the mixed-model for EMA1 – “how satisfied were you with the

visual comfort of the electric lighting in your work area?” (a) main effect of CCT and two-way interaction between

daylight access and CCT, and lumen output and CCT (similar patterns can be obtained from Web1); (b) the three-way

interaction plots. Responses were coded on a 0-100 scale, with 0 indicating very unsatisfactory and 100 indicating very

satisfactory. In order to show the difference clearly, only 20 – 80 out of 100 are shown here.

54.80

43.71

20

50

80

3500 5000

Rat

ing

CCT (K)

52.30

57.29

48.34

39.09

2330 3000Lumen output (lm)

3500 K

5000 K

51.20

58.39

48.76

38.67

No YesDaylight accessibility

3500 K

5000 K

54.62

62.16

46.46

30.88


With daylight access

3500 K

5000 K

49.98

52.4250.22

47.30

20

50

80

2330 3000

Rat

ing

Lumen output (lm)

Without daylight access

3500 K

5000 K

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Figure 6 Main effect of CCT, two-way interaction between daylight accessibility, and between lumen output and CCT

plots that were significant factors in the mixed-model in Web3 – “Overall, I am satisfied with the lighted environment of

my work area”. Similar pattern can be obtained from two questions in web-based surveys regarding overall satisfaction

(Web2 and Web4).

4.70

3.55

1

2

3

4

5

6

7

3500 5000

Rat

ing

CCT (K)

4.544.85

3.86 3.24


3500 K

5000 K

4.42

4.97

3.903.20


3500 K

5000 K

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Figure 7 Main effect of CCT, lumen output, two-way interaction between lumen output and CCT plots that were

significant factors in the mixed-model in EMA2 – “how bright was the lighting in your work area?” Similar pattern can

be obtained from Web7 as shown in Figure 8. Responses were coded on a 0-100 scale, with 0 indicating too dim and 100

indicating too bright. In order to show the difference clearly, only 20 – 80 out of 100 are shown here.

50.70

55.39

20

50

80

3500 5000

Rat

ing

CCT (K)

51.50

54.59


52.83

48.5750.17

60.61


3500 K

5000 K

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Figure 8 Main effect of CCT, lumen output, two-way interaction between daylight accessibility, and between lumen

output and CCT plots that were significant factors in the mixed-model in Web7 – “The quantity of electric lighting for

the work that I do is:”.

3.04

3.43


3.10

3.37

1

2

3

4

5

3500 5000CCT (K)

3.11 3.08

2.96

3.78


3500 K

5000 K

3.45

2.62

3.523.34


2330 lm

3000 lm

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Figure 9 Main effect of CCT, two-way interaction between daylight accessibility, and between lumen output and CCT

plots that were significant factors in the mixed-model in EMA3 – “the color temperature of the electric lighting in your

work area was:”. Responses were coded on a 0-100 scale, with 0 indicating too cool and 100 indicating too warm. In

order to show the difference clearly, only 20 – 80 out of 100 are shown here.

49.61

35.75

20

50

80

3500 5000

Rat

ing

CCT (K)

46.58

52.64

40.3331.18


3500 K

5000 K

47.7751.45

42.35

29.15


3500 K

5000 K

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Figure 10 Main effect of CCT, two-way interaction between lumen output and CCT plots that were significant factors in

the mixed-model in Web8 – “the color temperature of the electric lighting is pleasing.”

4.11

3.00

1

2

3

4

5

6

7

3500 5000

Rat

ing

CCT (K)

4.01 4.21

3.402.60


3500 K

5000 K

Very Strongly Agree

Very Strongly Disagree

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(a) (b)

Figure 11 Main effect of CCT for Web9 and Web10. (a) Web9 – “I would prefer the color temperature of the electric

lighting to be warmer.” (b) Web10- “I would prefer the color temperature of the electric lighting to be cooler.”

4.10

5.24

1

2

3

4

5

6

7

3500 5000

Rat

ing

CCT (K)

Very Strongly Agree


3.27

2.46

1

2

3

4

5

6

7

3500 5000

Rat

ing

CCT (K)

Very Strongly Agree


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Figure 12 Main effect of CCT, the two-way interaction between daylight accessibility and CCT, and between lumen

output and CCT for Web11 – “during the past 5 work days, the quality of light in this part of the building had a negative

effect on my work performance.”

3.57

4.21

1

2

3

4

5

6

7

3500 5000

Rat

ing

CCT (K)

3.64 3.50

3.88

4.54


3500 K

5000 K

3.80

3.333.82

4.60


3500 K

5000 K

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Figure 13 Main effect of CCT and the two-way interaction between daylight accessibility and CCT for Web12 – “please

estimate how your productivity was increased or decreased during the last 5 work days by the lighting conditions in

this building?” (ratings were converted from the choices of percentage: 1. -20%, 2. -10%, 3. -5%, 4. 0%, 5. +5%, 6. +10%,

7. +20%).

4.02 3.49

1

2

3

4

5

6

7

3500 5000

Rat

ing

CCT (K)

3.854.19

3.79 3.20


3500 K

5000 K

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Figure 14 Main effects of CCT and lumen output for Web15 – “the amount of reflected light or glare in my computer

screen is problematic.”

2.60

3.10


2.60

3.09

1

2

3

4

5

6

7

3500 5000

Rat

ing

CCT (K)

Very Strongly Agree


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Tables

Table 1 Index of the four treatment conditions provided by different lamp types (A, B, C, and D) with corresponding

nominal CCT and lumen output. The order of treatment condition experienced by the participants was from A to D. A

and C had a CRI of 85; B and D had a CRI of 82. The rated lumen output of B and C was 2935 and 3000 lm, respectively..

The measures related to S/P ratio for each lamp type are summarized in (b)

(a)

(b)

2330 ≈ 3000

3500 A C

5000 D B

Lumen Output (lm)

CCT (K)

S/P (S/P)0.5

(S/P)0.78

A 1.40 1.18 1.30

B 1.92 1.39 1.66

C 1.42 1.19 1.31

D 1.90 1.38 1.65

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Table 2 Summary of the questions in EMAs and responses given by the participants under each treatment condition.

No. of

responsesMean Std. Dev.

No. of

responsesMean Std. Dev.

A 84 55.73 17.80 70 50.67 12.13

B 89 29.55 21.31 75 48.24 16.70

C 67 61.91 14.74 68 55.65 14.91

D 84 45.54 18.80 88 50.91 14.37

A 84 47.61 9.91 70 54.60 13.15

B 89 58.51 22.41 75 63.60 17.00

C 67 50.96 8.71 68 52.82 11.83

D 84 46.35 17.13 88 53.43 15.29

A 84 48.65 10.00 70 48.71 12.76

B 89 22.26 21.63 75 42.88 17.18

C 67 55.72 9.09 68 53.76 12.16

D 84 34.74 20.47 88 45.06 14.42

Too cool

-

Too warm

Response

(0-100)

Lamp

Type

EMA1

EMA2

EMA3

Considering your time at work

this morning (afternoon), how

bright was the lighting in your

work area?


this morning (afternoon), how

satisfied were you with the visual

comfort of the electric lighting in

your work area?


this morning (afternoon), the

color temperature of the electric

lighting in your work area was:

With daylight access Without daylight access

Question

Too dim

-

Too bright

Very

unsatisfactory

-

Very

satisfactory

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Table 3 Summary of the questions in web-based surveys and responses given by the participants under each treatment

condition. All questions except Web7 and Web12 were scaled on a seven-point Likert scale (where 1 = Strongly disagree

and 7 = Strongly agree) The scaling for Web7 and Web12 is as noted within the table.

Lamp

Type

No. of

responseMean

Std.

dev.

No. of

responseMean

Std.

dev.

A 10 4.60 0.66 10 3.80 0.98

B 10 2.30 1.35 11 3.36 1.37

C 8 4.88 0.93 9 4.00 1.05

D 10 3.50 1.43 12 3.58 1.26

A 10 5.10 1.22 10 3.80 1.17

B 10 3.30 1.73 11 3.73 1.60

C 8 5.38 0.70 10 4.30 1.00

D 10 4.20 1.47 12 4.00 1.00

A 10 4.80 1.17 10 4.30 0.64

B 10 2.60 2.01 11 3.91 1.50

C 8 5.25 0.83 10 4.50 0.92

D 10 3.80 1.72 12 3.92 0.95

A 10 4.90 1.04 10 3.90 0.83

B 10 2.80 1.94 11 3.36 1.30

C 8 5.00 1.00 10 4.50 0.81

D 10 3.70 1.55 12 3.92 1.04

A 10 5.60 0.92 10 5.70 0.90

B 10 5.10 0.94 11 5.36 1.55

C 8 5.60 0.70 10 5.40 1.11

D 10 5.00 0.77 12 5.67 0.94

A 10 5.60 0.92 10 5.70 0.90

B 10 5.30 0.78 11 5.82 0.83

C 8 5.38 0.48 10 5.60 0.80

D 10 5.30 0.64 11 5.18 1.47

A 10 2.78 0.63 10 3.50 0.92

B 10 3.70 1.00 11 3.82 0.83

C 8 3.00 0.50 10 3.30 0.78

D 10 2.50 1.02 12 3.42 1.04

A 10 3.90 1.04 10 3.80 0.87

B 10 2.10 1.37 11 3.55 1.62

C 8 4.50 0.87 10 4.20 0.75

D 10 3.10 1.37 12 3.33 1.49

A 10 4.30 1.00 10 4.80 1.54

B 10 5.90 1.45 11 4.91 1.44

C 8 3.38 0.70 10 4.00 1.55

D 10 5.40 1.36 12 4.67 1.43

A 10 3.00 1.41 10 3.20 1.54

B 10 2.10 1.45 11 2.55 1.44

C 8 3.75 1.39 9 3.22 1.87

D 10 2.20 1.08 12 3.08 1.50

A 10 3.30 0.78 10 4.00 0.89

B 10 5.10 1.30 11 4.00 1.04

C 8 3.25 1.09 10 3.60 0.80

D 10 4.10 1.45 12 3.67 0.62

A 10 4.00 0.77 10 4.00 1.00

B 10 3.10 0.83 11 3.91 1.08

C 8 3.50 1.80 10 3.70 0.46

D 10 3.30 1.00 6 3.49 1.68

A 10 3.10 0.94 9 3.33 0.67

B 10 3.80 1.47 11 3.45 1.23

C 8 2.88 0.93 10 3.40 1.11

D 10 3.70 1.00 12 3.50 1.32

A 10 5.10 0.94 9 4.40 0.49

B 10 4.80 1.17 11 4.55 2.02

C 8 5.38 0.70 10 4.80 1.17

D 10 5.30 1.02 12 4.67 0.62

A 10 2.40 1.20 10 2.40 1.02

B 10 3.70 1.19 11 3.09 0.79

C 8 2.75 0.97 10 2.80 0.87

D 10 2.90 1.04 12 2.67 0.85

The quantity of electric lighting for the work that I

do is (1: Too dim; 2: Just barely adequate; 3: Just

right; 4: Too much; 5: Too bright):

Web7

Web13

Web14

Please estimate how your productivity was

increased or decreased during the last 5 work days

by the lighting conditions in this building (1: -20%;

2: -10%; 3: -5%; 4: 0%; 5: +5%; 6: +10%; 7: +20%).

There is too much contrast on my work surface.

The light is appropriately distributed for my visual

tasks.

With daylight access Without daylight

Visual

comfort

Overall

satisfaction

I am satisfied with the visual comfort of the electric

lighting in my work area. Web1

Overall, I am satisfied with the lighted environment

of my work area.

Overall, I am satisfied with the electric lighting in

my work area.

Web2

Web3

Web4The lighting in my work area is pleasant to work

under.

Web5

There is enough light for computer work. Web6

Category Question

The amount of reflected light or glare in my

computer screen is problematic.Web15

Contrast

I would prefer the color temperature of the electric

lighting to be warmer.

Quantity

(brightness)

Color

temperature

Productivity

Web8

Web9

Web10

Web11

Web12

During the past 5 work days, the quality of light in

this part of the building had a negative effect on my

work performance.

I would prefer the color temperature of the electric

lighting to be cooler.

The color temperature of the electric lighting is

pleasing.

There is enough light to read printed materials at

my desk.

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Table 4 Summary of lighting belief questions included in the first and last web-based surveys, all of which were rated on

a seven-point Likert scale (where 1 = Strongly disagree and 7 = Strongly agree). Both paired sample t-test and Wilcoxon

signed-rank test were employed to test the difference between the two surveys, which provided similar results.

Mean Median Std. Dev. Mean Median Std. Dev.

LB1 Quality of light is important to my well-being. 5.5 6.0 1.47 5.5 5.0 1.28 0.908

LB2 Sunny days make me happy. 6.3 7.0 0.90 6.0 6.0 1.32 0.285

LB3 Bright lights are stimulating; they make me feel energetic. 4.3 4.0 1.27 4.2 4.0 1.18 0.582

LB4 I get eyestrain from working under fluorescent lights. 4.3 4.0 1.46 4.3 4.0 1.26 1.000

LB5 Incandescent lights are relaxing. 4.2 4.0 0.96 4.1 4.0 0.91 0.832

LB6 I work equally well in a room with any kind of lighting. 3.3 3.0 1.11 3.4 3.0 1.13 0.819

LB7 Bright light at work does not improve my morale. 3.8 4.0 1.22 3.8 4.0 1.23 0.764

LB8 The brighter the light, the more work I accomplish. 3.8 3.5 1.15 3.7 4.0 1.11 0.600

LB9 Bright, harsh fluorescent lighting can make me feel tense. 4.6 5.0 0.92 5.0 5.0 0.68 0.048

LB10 The quality of light in my workplace is irrelevant to my job satisfaction. 3.4 3.0 0.97 3.3 3.0 1.02 0.461

LB11 Natural daylight indoors improves my mood. 5.8 6.0 0.96 5.8 6.0 1.09 0.814

LB12 It makes no difference to me what kind of lighting is in a room. 2.8 3.0 1.22 2.8 3.0 0.85 1.000

LB13 I prefer soft, diffuse light in my office work environment. 4.8 5.0 1.17 5.0 5.0 1.07 0.294

LB14 Glaring lights give me headaches. 5.0 5.0 1.14 4.8 5.0 1.39 0.467

LB15 Reading under dim light does not damage your vision. 3.5 3.0 1.15 3.5 3.0 1.25 0.746

LB16 Fluorescent lights are bad for your health. 3.9 4.0 0.93 3.7 4.0 1.24 0.136

LB17 If I want to create an intimate setting, I dim the lights. 5.4 5.0 0.88 5.2 5.0 0.91 0.185

LB18 Fluorescent light seldom gives me a headache. 4.1 4.0 1.44 4.0 4.0 1.40 0.852

LB19 Lack of sunlight in winter does not bother me. 2.7 2.5 1.43 2.3 2.0 1.24 0.115

LB20 I do my best work in places that are lit using natural daylight. 5.2 5.0 1.35 5.1 5.0 1.27 0.713

LB21 I prefer to have control of the lighting in my workspace. 5.5 5.0 1.01 5.5 5.0 0.90 0.832

LB22 I like to have different light levels based on the task I am performing. 5.0 5.0 1.22 4.9 5.0 1.07 0.622

LB23 I like to have more light when I am working on a computer. 4.1 4.0 1.22 3.6 4.0 0.75 0.031

LB24 If the light is visually cool, my office environment feels uncomfortable. 3.7 4.0 0.91 4.4 5.0 1.42 0.005

Before After p-value of

paired t-testQuestion

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Table 5 Mean illuminances (lx) and standard deviations in three private offices (1. measured directly using an

illuminance meter in the experiment space; 2. calculated from the measurements; 3. one overhead luminaire was not

working when the measurements were taken).

Mean Std. dev. Mean Std. dev. Mean Std. dev. Mean Std. dev.

Daylight only 1

291.6 215.19 394.8 325.06 236.0 160.06 64.2 74.99

Daylight + overhead

luminaires 1 494.8 234.81 749.3 323.07 620.5 216.13 310.2 121.57

Overhead luminaires only 2

203.2 58.04 354.5 115.50 384.5 85.23 246.0 85.36

Daylight only 1 379.5 246.41 370.5 189.91 298.9 148.66 8.0 3.16

Daylight + overhead

luminaires 1 568.4 293.18 688.4 268.68 587.3 198.48 199.5 59.03

Overhead luminaires only 2 188.9 51.97 317.9 93.60 288.4 74.48 191.5 56.25


Overhead + undercabinet

task light 1 653.0 126.62 873.7 141.74 630.83 125.89 773.8 137.77

Overhead + undercabinet

task + table lamp 1 803.0 208.08 1013.2 173.15 766.63 178.55 898.8 154.77

Office C

Lamp type A Lamp type B Lamp type C Lamp type D

Office A

Office B

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Table 6 Statistical significance for the effects in linear mixed-model for the questions included in the EMAs and the

web-based surveys, and the statistical significance for the comparisons between three pairs of lamp types.

EMA1 Web1 Web2 Web3 Web4 Web5 Web6 Web7 EMA2 Web8 EMA3 Web9 Web10 Web11 Web12 Web13 Web14 Web15

CCT < 0.001 < 0.001 0.005 < 0.001 0.001 0.221 0.286 0.056 0.001 0.001 < 0.001 < 0.001 0.002 0.016 0.015 0.072 0.285 0.019

Lumen 0.199 0.175 0.440 0.516 0.268 0.449 0.731 0.009 0.037 0.985 0.301 0.400 0.901 0.215 0.881 0.994 0.314 0.020

Daylight 0.737 0.676 0.250 0.867 0.686 0.458 0.459 0.131 0.211 0.427 0.360 0.794 0.672 0.618 0.535 0.991 0.446 0.467

CCT × Lumen < 0.001 0.039 0.062 0.042 0.023 0.826 0.268 0.010 < 0.001 0.047 < 0.001 0.003 0.126 0.038 0.968 0.903 0.613 0.590

CCT × Daylight < 0.001 0.018 0.029 0.031 0.064 0.367 0.821 0.843 0.968 0.113 < 0.001 0.016 0.103 0.019 0.029 0.210 0.195 0.336

Daylight × Lumen 0.253 0.432 0.373 0.266 0.385 0.450 0.244 0.027 0.490 0.436 0.097 0.836 0.268 0.196 0.773 0.867 0.930 0.608

0.011 0.215 0.715 0.156 0.828 0.754 0.686 0.712 0.400 0.086 0.066 0.509 0.958 0.701 0.168 0.849 0.309 0.748

0.728 0.764 0.632 0.662 0.730 0.820 0.562 0.436 0.603 0.839 0.558 0.539 0.478 0.938 0.731 0.796 0.772 0.766

0.004 0.070 0.177 0.019 0.045 0.760 0.627 1.000 0.177 0.044 < 0.001 0.018 0.066 0.436 0.507 0.272 0.130 0.778

0.100 0.106 0.172 0.023 0.044 0.080 0.226 0.759 0.560 0.077 < 0.001 0.108 0.275 0.418 0.292 0.227 0.326 0.284

<0.001 0.014 0.027 0.016 0.018 0.793 0.484 0.007 < 0.001 0.036 < 0.001 0.012 0.026 0.035 0.251 0.289 0.436 0.103

p-value of the comparison

between lamp type A and D


between lamp type B and C


between lamp type C and D

Productivity Contrast and GlareQuantity (brightness) Color Temperature

Three-way

Two-

way

Main

Visual Comfort Overall Satisfaction

Pseudo R2

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Acknowledgements

We would like to thank Dr. Michael Royer from Pacific Northwest National Laboratory (PNNL)

for his help in this study. This study was supported by the Energy Efficient Buildings Hub

(EEB Hub), an energy innovation hub sponsored by the U.S. Department of Energy under

Award Number DE-EE0004261.

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Table 1

Lumen Output (lm)

2330 ≈ 3000

CCT (K) 3500 A C

5000 D B

S/P (S/P)0.5 (S/P)0.78

A 1.40 1.18 1.30

B 1.92 1.39 1.66

C 1.42 1.19 1.31

D 1.90 1.38 1.65

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Table 2

Question Response (0-100)

Lamp Type

With daylight access Without daylight access

No. of responses

Mean Std. Dev. No. of

responses Mean Std. Dev.

EMA1

Considering your time at work this morning (afternoon), how satisfied were you with the visual

comfort of the electric lighting in your work area?

Very unsatisfactory

-

Very satisfactory

A 84 55.73 17.80 70 50.67 12.13

B 89 29.55 21.31 75 48.24 16.70

C 67 61.91 14.74 68 55.65 14.91

D 84 45.54 18.80 88 50.91 14.37

EMA2

Considering your time at work this morning (afternoon), how bright was the lighting in your work area?

Too dim -

Too bright

A 84 47.61 9.91 70 54.60 13.15

B 89 58.51 22.41 75 63.60 17.00

C 67 50.96 8.71 68 52.82 11.83

D 84 46.35 17.13 88 53.43 15.29

EMA3

Considering your time at work this morning (afternoon), the color temperature of the electric lighting in your work area was:

Too cool -

Too warm

A 84 48.65 10.00 70 48.71 12.76

B 89 22.26 21.63 75 42.88 17.18

C 67 55.72 9.09 68 53.76 12.16

D 84 34.74 20.47 88 45.06 14.42

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Table 3

Category Question

With daylight access Without daylight

access

Lamp Type

No. of response

Mean Std. dev.

No. of

response Mean

Std. dev.

Visual comfort

Web1 I am satisfied with the visual comfort of the electric lighting in my work area.

A 10 4.60 0.66 10 3.80 0.98

B 10 2.30 1.35 11 3.36 1.37

C 8 4.88 0.93 9 4.00 1.05

D 10 3.50 1.43 12 3.58 1.26

Overall satisfaction

Web2 Overall, I am satisfied with the lighted environment of my work area.

A 10 5.10 1.22 10 3.80 1.17

B 10 3.30 1.73 11 3.73 1.60

C 8 5.38 0.70 10 4.30 1.00

D 10 4.20 1.47 12 4.00 1.00

Web3

Overall, I am satisfied with the electric lighting in my work area.

A 10 4.80 1.17 10 4.30 0.64

B 10 2.60 2.01 11 3.91 1.50

C 8 5.25 0.83 10 4.50 0.92

D 10 3.80 1.72 12 3.92 0.95

Web4 The lighting in my work area is pleasant to work under.

A 10 4.90 1.04 10 3.90 0.83

B 10 2.80 1.94 11 3.36 1.30

C 8 5.00 1.00 10 4.50 0.81

D 10 3.70 1.55 12 3.92 1.04

Quantity (brightness)

Web5 There is enough light to read printed materials at my desk.

A 10 5.60 0.92 10 5.70 0.90

B 10 5.10 0.94 11 5.36 1.55

C 8 5.60 0.70 10 5.40 1.11

D 10 5.00 0.77 12 5.67 0.94

Web6 There is enough light for computer work.

A 10 5.60 0.92 10 5.70 0.90

B 10 5.30 0.78 11 5.82 0.83

C 8 5.38 0.48 10 5.60 0.80

D 10 5.30 0.64 11 5.18 1.47

Web7 The quantity of electric lighting for the work that I do is (1: Too dim; 2: Just barely adequate; 3: Just right; 4: Too much; 5: Too bright):

A 10 2.78 0.63 10 3.50 0.92

B 10 3.70 1.00 11 3.82 0.83

C 8 3.00 0.50 10 3.30 0.78

D 10 2.50 1.02 12 3.42 1.04

Color temperature

Web8 The color temperature of the electric lighting is pleasing.

A 10 3.90 1.04 10 3.80 0.87

B 10 2.10 1.37 11 3.55 1.62

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C 8 4.50 0.87 10 4.20 0.75

D 10 3.10 1.37 12 3.33 1.49

Web9 I would prefer the color temperature of the electric lighting to be warmer.

A 10 4.30 1.00 10 4.80 1.54

B 10 5.90 1.45 11 4.91 1.44

C 8 3.38 0.70 10 4.00 1.55

D 10 5.40 1.36 12 4.67 1.43

Web10 I would prefer the color temperature of the electric lighting to be cooler.

A 10 3.00 1.41 10 3.20 1.54

B 10 2.10 1.45 11 2.55 1.44

C 8 3.75 1.39 9 3.22 1.87

D 10 2.20 1.08 12 3.08 1.50

Productivity

Web11 During the past 5 work days, the quality of light in this part of the building had a negative effect on my work performance.

A 10 3.30 0.78 10 4.00 0.89

B 10 5.10 1.30 11 4.00 1.04

C 8 3.25 1.09 10 3.60 0.80

D 10 4.10 1.45 12 3.67 0.62

Web12

Please estimate how your productivity was increased or decreased during the last 5 work days by the lighting conditions in this building (1: -20%; 2: -10%; 3: -5%; 4: 0%; 5: +5%; 6: +10%; 7: +20%).

A 10 4.00 0.77 10 4.00 1.00

B 10 3.10 0.83 11 3.91 1.08

C 8 3.50 1.80 10 3.70 0.46

D 10 3.30 1.00 6 3.49 1.68

Contrast

Web13 There is too much contrast on my work surface.

A 10 3.10 0.94 9 3.33 0.67

B 10 3.80 1.47 11 3.45 1.23

C 8 2.88 0.93 10 3.40 1.11

D 10 3.70 1.00 12 3.50 1.32

Web14 The light is appropriately distributed for my visual tasks.

A 10 5.10 0.94 9 4.40 0.49

B 10 4.80 1.17 11 4.55 2.02

C 8 5.38 0.70 10 4.80 1.17

D 10 5.30 1.02 12 4.67 0.62

Web15 The amount of reflected light or glare in my computer screen is problematic.

A 10 2.40 1.20 10 2.40 1.02

B 10 3.70 1.19 11 3.09 0.79

C 8 2.75 0.97 10 2.80 0.87

D 10 2.90 1.04 12 2.67 0.85

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Table 4

Question

Before After p-value of

paired t-test Mean Median Std. Dev.

Mean Median Std. Dev.

LB1 Quality of light is important to my well-being. 5.5 6.0 1.47 5.5 5.0 1.28 0.908

LB2 Sunny days make me happy. 6.3 7.0 0.90 6.0 6.0 1.32 0.285

LB3 Bright lights are stimulating; they make me feel energetic. 4.3 4.0 1.27 4.2 4.0 1.18 0.582

LB4 I get eyestrain from working under fluorescent lights. 4.3 4.0 1.46 4.3 4.0 1.26 1.000

LB5 Incandescent lights are relaxing. 4.2 4.0 0.96 4.1 4.0 0.91 0.832

LB6 I work equally well in a room with any kind of lighting. 3.3 3.0 1.11 3.4 3.0 1.13 0.819

LB7 Bright light at work does not improve my morale. 3.8 4.0 1.22 3.8 4.0 1.23 0.764

LB8 The brighter the light, the more work I accomplish. 3.8 3.5 1.15 3.7 4.0 1.11 0.600

LB9 Bright, harsh fluorescent lighting can make me feel tense. 4.6 5.0 0.92 5.0 5.0 0.68 0.048

LB10 The quality of light in my workplace is irrelevant to my job satisfaction. 3.4 3.0 0.97 3.3 3.0 1.02 0.461

LB11 Natural daylight indoors improves my mood. 5.8 6.0 0.96 5.8 6.0 1.09 0.814

LB12 It makes no difference to me what kind of lighting is in a room. 2.8 3.0 1.22 2.8 3.0 0.85 1.000

LB13 I prefer soft, diffuse light in my office work environment. 4.8 5.0 1.17 5.0 5.0 1.07 0.294

LB14 Glaring lights give me headaches. 5.0 5.0 1.14 4.8 5.0 1.39 0.467

LB15 Reading under dim light does not damage your vision. 3.5 3.0 1.15 3.5 3.0 1.25 0.746

LB16 Fluorescent lights are bad for your health. 3.9 4.0 0.93 3.7 4.0 1.24 0.136

LB17 If I want to create an intimate setting, I dim the lights. 5.4 5.0 0.88 5.2 5.0 0.91 0.185

LB18 Fluorescent light seldom gives me a headache. 4.1 4.0 1.44 4.0 4.0 1.40 0.852

LB19 Lack of sunlight in winter does not bother me. 2.7 2.5 1.43 2.3 2.0 1.24 0.115

LB20 I do my best work in places that are lit using natural daylight. 5.2 5.0 1.35 5.1 5.0 1.27 0.713

LB21 I prefer to have control of the lighting in my workspace. 5.5 5.0 1.01 5.5 5.0 0.90 0.832

LB22 I like to have different light levels based on the task I am performing. 5.0 5.0 1.22 4.9 5.0 1.07 0.622

LB23 I like to have more light when I am working on a computer. 4.1 4.0 1.22 3.6 4.0 0.75 0.031

LB24 If the light is visually cool, my office environment feels uncomfortable. 3.7 4.0 0.91 4.4 5.0 1.42 0.005

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Table 5

Lamp type A Lamp type B Lamp type C Lamp type D

Mean Std. dev.

Mean Std. dev.

Mean Std. dev.

Mean Std. dev.

Office A

Daylight only 1

291.6 215.19 394.8 325.06 236.0 160.06 64.2 74.99

Daylight + overhead luminaires 1 494.8 234.81 749.3 323.07 620.5 216.13 310.2 121.57


Office B

Daylight only 1 379.5 246.41 370.5 189.91 298.9 148.66 8.0 3.16

Daylight + overhead luminaires 1

568.4 293.18 688.4 268.68 587.3 198.48 199.5 59.03


188.9 51.97 317.9 93.60 288.4 74.48 191.5 56.25

Office C


545.8 127.54 709.8 177.83 443.33 110.64 576.2 145.58

Overhead + undercabinet task light 1

653.0 126.62 873.7 141.74 630.83 125.89 773.8 137.77

Overhead + undercabinet task + table lamp 1

803.0 208.08 1013.2 173.15 766.63 178.55 898.8 154.77

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Table 6

Visual Comfort Overall Satisfaction Quantity (brightness) Color Temperature Productivity Contrast and Glare

EMA1 Web1 Web2 Web3 Web4 Web5 Web6 Web7 EMA2 Web8 EMA3 Web9 Web10 Web11 Web12 Web13 Web14 Web15

Main CCT < 0.001 < 0.001 0.005

< 0.001 0.001 0.221 0.286 0.056 0.001 0.001 < 0.001 < 0.001 0.002 0.016 0.015 0.072 0.285 0.019

Lumen 0.199 0.175 0.440 0.516 0.268 0.449 0.731 0.009 0.037 0.985 0.301 0.400 0.901 0.215 0.881 0.994 0.314 0.020

Daylight 0.737 0.676 0.250 0.867 0.686 0.458 0.459 0.131 0.211 0.427 0.360 0.794 0.672 0.618 0.535 0.991 0.446 0.467

Two-way

CCT × Lumen < 0.001 0.039 0.062 0.042 0.023 0.826 0.268 0.010 < 0.001 0.047 < 0.001 0.003 0.126 0.038 0.968 0.903 0.613 0.590

CCT × Daylight < 0.001 0.018 0.029 0.031 0.064 0.367 0.821 0.843 0.968 0.113 < 0.001 0.016 0.103 0.019 0.029 0.210 0.195 0.336

Daylight × Lumen 0.253 0.432 0.373 0.266 0.385 0.450 0.244 0.027 0.490 0.436 0.097 0.836 0.268 0.196 0.773 0.867 0.930 0.608

Three-way 0.011 0.215 0.715 0.156 0.828 0.754 0.686 0.712 0.400 0.086 0.066 0.509 0.958 0.701 0.168 0.849 0.309 0.748

Pseudo R2 0.728 0.764 0.632 0.662 0.730 0.820 0.562 0.436 0.603 0.839 0.558 0.539 0.478 0.938 0.731 0.796 0.772 0.766

p-value of the comparison between lamp type C and D

0.004 0.070 0.177 0.019 0.045 0.760 0.627 1.000 0.177 0.044 < 0.001 0.018 0.066 0.436 0.507 0.272 0.130 0.778

p-value of the comparison between lamp type A and D

0.100 0.106

0.172 0.023 0.044

0.080 0.226 0.759 0.560

0.077 < 0.001 0.108 0.275

0.418 0.292

0.227 0.326 0.284

p-value of the comparison between lamp type B and C

<0.001 0.014 0.027 0.016 0.018 0.793 0.484 0.007 < 0.001 0.036 < 0.001 0.012 0.026 0.035 0.251 0.289 0.436 0.103

Documents

Field study of office worker responses to fluorescent lighting of different CCT and lumen output