LdG-01 Lighting design Guide for offices

LdG-1 Lighting design Guide for offices Ezzat Baroudi

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LdG-1 Lighting design Guide for offices

Introduction

The importance of office lighting to achieve basic requirements relating to the health and

safety of people at work is crucial, that is why it is the first one in my series of lighting

guides.

In this guide I will be addressing the following

1. The European standard about lighting EN 12464-1: “The Lighting of Workplaces”

with explanation of different parts.

2. The DIAL investigation (a research carried out to show the effect of different lighting

scenes in office lighting).

3. Case Study of office lighting.

4. How to use DIALux evo to calculate the requirements of office lighting.

EN 12464-1: “The Lighting of Workplaces” This European standard is about the quality aspects of lighting workstations and their direct

environment. It also has tables with lighting requirements in accordance with the type of

work and the visual task.

1) working Plane The working plane in office area is considered

0.75 or 0.8 form floor level which is the

standard height of a table.

When standard is asking for 500 Lux it should

be achieved at this height for the office area.

In this guide 0.75 will be considered as the

height for the office area.

The working plane for a corridor is 0.2


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2) Task Area The task defines the size of the working plane for calculation inside a space and could have

of the following situation

A. the location of the workstation is not known during design stage then the whole room will be taken as a task Area The wall Zone of 0.5 could be ignored if the workstation is not placed near wall. The wall zone will not be taken into consideration for the average value of Lux or uniformity.

B. The location of the workstation is not known during design stage and there is a possibility to place work station near wall then the whole room will be taken as a task Area.

C. The location of the workstation is known then task area is above the desk typically 1.8 m x 1.8 m (the blue area in the side image) the minimum dimensions of an office desk are 1.6 m x 0.8 m. The surrounding area is an area around the task area with at least 0.5 meter form all sides (the purple area in the next image) Background area is the area of the other space and should be at least It should be at least 3.0 m wide. Wall zone of 0.5 m could be considered


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3) Lighting requirements for office area The table below has the regiments of different office spaces where

Em is the Minimum Illuminance in lux

UGRL is maximum limit for Unified Glare Rating

Uo is the uniformity of lighting (Emin / Eaverage)

Ra is the minimum color rendering of the lamp

Interior type, task or activity Em (lx) UGRL Uo Ra

Filing, copying, etc. 300 19 0.4 80 Writing, typing, reading, data processing 500 19 0.6 80 Technical drawing 750 16 0.7 80 CAD work stations 500 19 0.6 80 Conference and meeting rooms 500 19 0.6 80 Reception desk 300 22 0.6 80 Archives 200 25 0.4 80

The requirement of Em (minimum Illuminance value In lux) could be taken form the table Example of office area where the requirement is 500 lx for data processing 500 Lux for the Task Area 300 Lux for Surrounding area 100 Lux for the Background area The Uo for the task area should be 0.6 which means that the minimum value should not be less than 60% of the average Value , e.g. if the achieved average value is 520 lx then the minimum should not be less than 312 lx

The UGR is an approximate model that express the chance of direct glare by Luminaire, the higher the figure, the greater the chance of glare.

Example of office area where the requirement of UGR limit is 19 then value should not exceed 19; it could be lower or equal 19


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It is good to understand the glare to understand the UGR formula Glare Glare is difficulty seeing in the presence of bright light against darker surrounding. Glare is caused by a significant ratio of luminance between the task and the background The high contrast make seeing more difficult and a good example is the head light of the car where at day time there is no high contrast between the headlight and the background then there is no glare, but at night where headlight is much higher than the surrounding (background) then it could cause glare especially if there is no street light (darker background)

High contrast at night between the headlight and the background

Low contrast at day time

Glare could be classified as

Disability glare Discomfort glare

Where the disability glare could be found mostly outdoor and can cause disability of vision, the discomfort glare where present will not disable the vision but will make the environment not comfortable. There are two types of discomfort glare

Direct glare Reflected glare


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Reflected glare Direct glare for luminaires

To reduce glare Fist selects the right luminaire that reduces the light that is coming to the eyes The light coming from the angles between 45o and 85o should be minimum The light form 45o to 65o

is less critical than the light from 650 to 85o

Luminaire with good cut-off angles that cut the light above 65o

Luminaire without cut off angle

Secondly reduce the contrast between the luminaire and the background by ensuring good light at ceiling and walls.


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UGR factors Let us have a look at the factors that could increase or decrease the UGR values

The “8“ is just a constant factor that gives the UGR numbers which normally sit in a range between 10 and 30

This takes into account that our eyes respond logarythmically to light

This is the background luminance, the higher it is the lower is the UGR value

The luminance of one luminaire squared

The solid angle of the lumi-naire from the observer‘s position represents the size of the glare source

The so-called Guth index represents the position of the luminaire in relation to the line of sight of the observer. It gets bigger the further it is away.

Form the formula above, we can see that the following will affect the UGR

1. Luminance of the luminaire 2. The luminance of the background 3. The position of the luminaries

So to keep the UGR low we have to follow the following steps

1. Select the right luminaire with low luminance (low brightness) at angles between 65o and 85o.

2. Consider a good position for luminaire in relation to the observer (software like DIALux could be helpful in this case).

3. Increasing the brightness of the background (walls and ceiling) For more information on luminance you can see the following link http://ezzatbaroudi.wordpress.com/2013/06/21/using-a-quantitative-measure-to-achieve-a-qualitative-lighting-design-effect/


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Luminaire The standard set new values for the maximum luminance of luminaires as shown in the following table

Table 4 gives the limits of the average luminaire luminance at elevation angles of 65° and above from the downward vertical, radially around the luminaires, for work stations where display screens which are vertical or inclined up to 15° tilt angle are used. Nowadays most if not all computer screen has high luminance so we can neglect the right column and use the left one where in case A the luminaire Luminance has to be less than 3000 cd/m2 at elevation angles of 65° of the luminaire.


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You can evaluate this value by using the photometric data in a computer software like DIALux evo you could see the curve that represents the values at different angles Red for 65° Blue for 75° Green for 85° All the values has to be less than 3000 cd/m2 In case the user is going to use negative polarity software like AutoCAD with black background the values has to be less than 1500cd/m2 For more information on this topic see

http://ezzatbaroudi.wordpress.com/2013/06/21/using-a-quantitative-measure-to-achieve-a-qualitative-lighting-design-effect/


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4) Vertical surfaces, Vertical task Area Shelving systems and cabinets need to be regarded vertical task areas if visual tasks need to be performed there over an extended period of time (e.g. ticket-issuing or bookkeeping). The vertical task area reference surface starts 0.5 m above floor level and, in the case of an office shelving system, ends 2.0 m above floor level

Where visual tasks are performed mainly on a vertical plane, that plane is the task area. The vertical task area reference surface starts 0.5 m above floor level and, in the case of an office shelving system, ends 2.0 m above floor level


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5) Illuminance for walls and ceilings One new requirement in EN 12464-1 is balanced luminance distribution. This is achieved by taking account of the luminance of all surfaces, which is determined by the reflectance of the surfaces and the Illuminance on them. To avoid gloom, raise adaptation levels and Enhance visual comfort; room surfaces should be bright. Wall washing is a good technic to ensure bight walls and achieving good visual comfort

Using wallwasher- A luminaire that distribute the light to walls is a good technic to ensure bight walls

The EN-12464-1 recommends a minimum value wall and ceiling as follows, however for brighter appearance a higher value is considered good practice Wall 75 lx U0 ≥ 0,10 Ceiling 50 lx U0 ≥ 0,10 0.5 meter could be excluded form top and bottom of the wall and could be away 0.5 meter form the wall. The ceiling as well could exclude 1 m form each side



6) Modelling and cylindrical illuminance Ēz Modelling is a good yardstick for 3D perception of persons and objects in a room. It

expresses the balance between diffuse and directional light and is determined by

The ratio of cylindrical illuminance to horizontal illuminance at a given point (normally 1.2

m above floor level). As a rough guide, a value between 0.30 and 0.60 is an indicator

of good modelling: faces and bodies are not too dramatically shaded or sharply illuminated,

nor are they cast in a flat, dull light.

A high cylindrical illuminance is important for the perception of vertical planes and objects. It is enhancing particularly the recognition of faces. Maintained illuminance must be no lower than 50 lx. In places where good visual communication is crucial, e.g. in an office, meeting room or classroom, maintained illuminance should be raised to 150 lx. This requirement needs to be met at 1.2 m above floor level for seated persons and 1.6 m above floor level for persons standing in activity and interior areas.

To avoid shadows the cylindrical illuminance should be at least 0.3 of the horizontal illuminance.



The Effect of Different Lighting scenes in Office Lighting DIAL research The German institute for applied lighting DIAL has carried out a research on The Effect of

Different Lighting Sciences in Office Lighting.

This investigation had 20 different scenes with combination of ambient and accent lighting as

in the following table

5 type of ambient lighting

A. Direct ambient lighting by Down

lighting.

B. Direct/indirect lighting by suspended

luminaire.

C. Indirect lighting only

D. Direct ambient lighting and wall-

washing

E. Indirect lighting by wall-washing



For the above 5 ambient lighting scenes an accent lighting scene there was added

The four scenes added to the above 5 ambient lighting scenes

1. No accent lighting at all.

2. Accent lighting on table.

3. Accent lighting on wall.

4. Accent lighting on table and wall.



One of the accent lighting scene with ambient lighting

The combination of the ambient and accent

lighting scenes give total of 20 scenes

For example scene 19 is senses that have

ambient of direct by downlight and indirect

by wall-washing with accent lighting on table

and wall.



Some of the 20 scenes

The purpose of the investigation is to find out, what the best lighting scene is for each one of

the following criteria

1. Brightness

2. Attractiveness

3. Activation

4. Well-being

The results was displayed by tables that have both colors and numbers

Color representation

The greener the color the higher rating has

the scene in particular criteria

The other way round the red is the worst.



Number representation

Because color could be similar, a number

give more precise rating

The lower the value represents the better

rating for the scene in particular criteria.

The other way round the warmer the worse.

The rating was form 1 to 5

1 is the best , 5 is the worst

The results are show in the following tables

Brightness For the brightness the best scene was

Ambient wall-wash and Accent (1.93)

While the worst scene for brightness is only

direct lighting which is the most common

scene you can find in an office!

Attractiveness The most attractive scene was with value

(2.09)

Ambient lighting (Direct lighting + wall-

washing) and accent on table and wall.

The worst is the indirect lighting (3.81)



Activation The best scene to keep people active is two

scene with value of (2.32)

Indirect lighting with accent lighting on table

and wall

or Ambient lighting (Direct lighting + wall-

washing) and accent on table and wall.

The worst is indirect lighting

Well-being The best scene for well-being has the value

of (2.23) which is

Ambient lighting (Direct lighting + wall-

washing) and accent on table and wall

The worst is indirect lighting

My conclusions The results are self-explanatory but I would like to highlight some points

1. The most common office lighting I have experienced in many offices is

the direct lighting. Engineers love it!

Despite that the direct lighting being the most cost effective and best for

energy efficiency, but it is the worst for brightness perception, the

second worst for the rest scenes (attractiveness, activation and well-

being)!



2. Indirect lighting is the worst in 3 scenes (attractiveness, activation and

well-being)!

In my career I met many interior designers and Architects who thinks

the cove lighting and hidden lighting the best lighting! p

Just because we don’t see the source of light will never make lighting more attractive!

This is a fact that we see it in day lighting, we don’t like the cloudy atmosphere and we

prefer the sunny day in spite of the glare we get by the sun.

Indirect lighting we produce a shadow-less effect similar to the cloudy atmosphere!

Sunny day Cloudy day

But when accent lighting was added to indirect lighting, the result was dramatically

changed

Adding accent lighting on table and wall

changed the indirect lighting from worst scene

for attractiveness to be second best!


changed the indirect lighting from worst for

activation to the best!




changed the indirect lighting from worst for

well-being to be third level!

3. Many Engineers ask for very high uniformaty in all the room!

Uniformaty is required only in task area and adding accent lighting will change uniformaty

a lot and create a hight contrast.

Uniform lighitng by cloudy day None-uniform lighting by sunny day

If we want to take the best scene in DIAL results we find that Ambient lighting (Direct lighting

+ wall-washing) and accent on table and wall is close to the best in brightness and the best in the

rest criteria (attractiveness , activation and well being) which makes it very good guideline for

designing an office.

Of course there can’t be one rule or scene for every office every time and there are many other

factors but it could be very good idea to consider adding wall wash and accent lighting to

improve the office lighting in gerneral.





Case Study In the plan below we can see 5 deferent areas

1. Open plan office

2. Individual office (MD office)

3. Meeting room

4. Waiting area

5. Corridor



Many engineers like to design all the rooms by just putting 60x60 fluorescent luminaire in a grid system, the follow layout shows the most common lighting design by many engineers, which is fairly simple and doesn’t give any quality of lighting, according to DIAL investigation it is the worst for brightness perception, the second worst for the rest scenes (attractiveness, activation and well-being)!





Calculation and rendering was produced by DIALux evo

The luminaire used is 3x14w T5 fluorescent with very efficient luminaire and the average

illuminance is higher than 500 lux in all the room with very uniform lighting!



In the next layout I am going to purpose an alternative solution that have Ambient lighting (Direct lighting + wall-washing) and accent on table and walls (the secene that was found best in DIAL invastagating for office lighting)



The downlight (wf) is a downlight with ERCO 83238 with Extra wide distribution

Wallwasher (ww) ERCO 84014

Downlight with oval flood distribution for the corridor ERCO 80032

Spot light for accent lighting (S) ERCO 40104 to highlight the painting on the wall and the meeting

table on the MD office



Spacing and offset for wallwasher and spotlight for accent lighting

The role of thumb , wallwasher should have an offset form the wall of 1/3 the wall height and the

spacing between the wall-washers is equal to the offset (if wall height is 3 meter then the offset

form wall should be 1 meter and spacing is one meter)

Accent lighting for a 3 meter height wall should be 850-1000 mm as an offset form wall to have 30o

tilt.



Offset a is 1/3 of the wall height

Spacing d is equal to offset however some new

wallwasher form ERCO could be spaced up to

1.5 times the offset

Spotlight offset form wall for

accent lighting for a painting on walls

Downlight 60x60 solution Downlight+wall-wash and accent lighting





(blue Colored wall-wash added)

The paintings on wall are much more attractive

Using DIALux evo with EN12464

If you go to assessment tool in DIALux evo

and select the room then you can define the

area and DIALux evo will list all the

requirements according to EN12464-1, this is

not only for office but for any type of room.

If you go to calculation objects mode and

select visual task areas you can place on task

area and DIALux evo will simply create

surrounding area and background area.



Also you could place area of activity to

calculate the cylindrical illuminance.

You can in place calculation for the walls and

ceiling by selecting room main surfaces tool

In the calculation object tool you can draw a

calculation surface and get many results by just

selecting what is required for this example a

UGR and cylindrical illuminance is selected

It should be noted that UGR and cylindrical

illuminance for offices should be at a height of

1.2 meter which is the average height of the

eye for a seated person.



DIALux evo will show the EN requirements in the summary page

Documents

LdG-01 Lighting design Guide for offices