1 Visual Efects of Light

8/11/2019 1 Visual Efects of Light

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Visual Effects of

LightProf. Grega Bizjak, PhDLaboratory of Lighting and Photometry

Faculty of Electrical EngineeringUniversity of Ljubljana


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Light is life

If sun wouldturn off the

life on earthwould extinct

LightWarmth


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Sun as a deity (god)

Almost all old religions worship a sun as a deity to

assure that it will come out next morning also.


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Rhythm of light is rhythm of life

We dontworship sun

anymore butwe are still

dependent onits day-cycle.


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Rhythm of light: morning

There is very few light in themorning but it increases withthe time.

Colour of light changes from

red to orange and to yellow.Diurnal organisms starts with

activities which grow

together with the light.We are sleepy in the morning

and we are slowly startingout activities.


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Rhythm of light: day

Sun is high, there is plentyof bright white lightanywhere.

Diurnal organisms are atthe peak of theirabilities.

We are at the top of ourabilities also and at themiddle of our workingday (coincidence?).


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Rhythm of light: evening

In the evening, the lightturns red, and is slowly

decreasing.Diurnal animals are

getting less active andare preparing for the

resting part of the day.

We are tired so we areconcluding our work

and are also preparingfor the night.


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Rhythm of light: night

At night the light is dulland colorless.

Organisms are, withexception of nocturnal

ones, resting.

We are resting andgathering strengths for

the next day also.


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Visual and nonvisual effects of light

How light influences human being?VISION

HEALTH

FEELINGEMOTIONS

MIND

MOOD


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Visible & invisible light

The sun's rays that spread among the trees, we see onlybecause they are reflected by particles in the air mist.

Otherwise they would remain invisible to our eyes.

Light allowsus to use

one of thesenses -

vision


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Light is the main source of

information

Light not only enables but also affects our

perception of the environment.

We obtain over80% of information

from theenvironment

through the vision.


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How do we feel if we can not see?

What technology was developed because of vision:Written language, drawings, formulas, plans, photographs

LOST?!


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Human eye the visual organ

The human eye, one of the mostcomplete optical instruments.


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The human eye as a camera

or vice versa

Pupil, ocular lens andretina functionsimilarly to:

Aperture, lens andfilm (CCD sensor) ina camera.


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How do we see - retina

Retina contains foto-receptors that are sensitive to light.

Blind Spot

Macula with fovea(without choroid, whichwould reduce visual

acuity)


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Blind spot

Close your left eye and watch an apple with your righteye. Bring the image closer and suddenly orange will

disappears. Its image is located in the blind spot.(diameter 2 cm, distance between 12 cm)


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How do we see - receptors

Foto-receptors in the eye convert incident light into

pulses that nerves lead to the brain.


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Cones and Rods

Cones

There are 4.500.000 cones in

average eye. They are less sensitive to light. They distinguish colors. They are arranged mostly in

fovea and macula. They contribute to vision in well

lit environment photopic

vision.


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Cones and Rods

Rods

There are 90.000.000 rods in

average eye. They are more sensitive to light They cant distinguish colors. They are placed mostly outside

macula. They contribute to vision in

dark environment- scotopic

vision.


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Cones and Rods

In rods there is a pigmentrhodopsin, which consists of twoparts: opsin and retinal. Under

the influence of light, the retinalmoves and allows chemicalsubstances to break into theopsin which causes the nerve

cells to begin to emit actioncurrents.

Rhodopsin is red but bleaches

under the influence of light.

retinal in dark

retinal on light


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Cones and Rods

Your manor, which in sunny day looks like this ...


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Cones and Rods

... looks in the middle of the night like this.

A black spotin the middleis due to thefact that

there is norods in foveaandtherefore thisarea can notbe seen atnight.


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Characteristics of human eyes

Field of visionDynamic range

Visual acuity

Eye adaptation

Eye accommodation

Depth perception

Optical aberration


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Field of vision


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Field of vision

The approximatefield of vision ofa human eye is:

95 out,

75 down,

60 in,60 up.


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Luminance dynamic range

Daylightluminances

from 10 cd/m2

to 10+4 cd/m2

Road lightingluminances

from 10-2 cd/m2

to 10cd/m2

Moonlightluminances

from 10-6 cd/m2

to 10-2 cd/m2

Static contrast ratio (no adaptation) is 1:100;

dynamic range (with adaptation) is 1:1.000.000.

Temperaturerange ?

from 15 Cto 25 C


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Visual acuity

Vision 6/6 (20/20):gap is seen from distance of 6 m

the size of the gap is so, thatfrom the distance of 6 m

represent 1 arc minute.

Visual acuity is a measureof the spatial resolution;ability to see a gap in a

broken ring.


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Visual acuity

Maximum visual acuity is in centre of the field of visionbecause of the densely packed cones in the fovea.

Visualacuity

deteriorateswith age.


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Eye adaptation

Eye adaptation is the ability of the eye to adjust

to various levels of darkness and light


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Eye adaptation

A minor mechanism of adaptation isthe pupullary light reflex, adjusting the

amount of light that reaches the retina.

Changes in the sensitivity of rods andcones in the eye are the major

contributors to dark adaptation.

The eye takes approximately 20 30 minutes to fully adapt frombright sunlight to completedarkness.

minutes

relativesensitivity


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Eye accommodation

Accommodation is the ability of the eye to

focus objects lying at different distances.


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Eye accommodation

The amplitude ofaccommodation is

influenced by theluminance level to

which the eye isadapted.

The amplitude ofaccommodation

declines with age.

amp

litudeofaccom

modation


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Depth perception

Depth perception is the ability to see the world in three

dimensions and to perceive distance.

Depth perception arises from a variety ofdepth cues:

binocular cues that require input from

both eyes andmonocular cues that require the input

from just one eye.

Binocular cues:stereopsis,

convergence,shadow stereopsis.


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Depth perception

Monocular cues provide

depth information whenviewing a scene with one

eye (or on picture):motion parallax,

perspective,familiar size,

aerial perspective,accommodation,

peripheral vision,texture gradient,lighting and shading.


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Depth perception

But themonocular

cues arenot always

reliable

opticalillusions.


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Depth perception

So we can notalways rely on

familiar size


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Optical aberration

Optical aberration is an imperfection in image

formation by an optical system

Spherical aberration,which occurs when light

rays strike a lens or mirrornear its edge

Chromatic aberration,

caused by differences inrefractive index for

different wavelengths oflight


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Functioning of the eye - vision

The human eye distinguishes following:

difference in brightness

difference in color

shape

movements or motion

distanceBut only if there is enough light. Better the lighting

conditions better the performance of the eye.


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Functioning of the eye - vision

Four minimum requirements need tobe met to permit perception!


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Minimum luminance

of observedobjects andsurroundings

Objects that can be easily identified in detailduring the day become indistinct at twilight and

are no longer perceptible in darkness.


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Minimum size

Objects need to be of am inim um size !Objects need to be of a m inim um size !

Objects need to be of a m inim um size !Objects need to be of a m inim um size !Objects need to be of a m inim um size !

Objects need to be of am inimum size !Objects need to be of a m inimum size !

Objects need to be of am inim um size !Objects need to be of a m inim um size!

Objects need to be of am inimum size!Objects need to be of a m inimum size!

Objects need to be of a minim um size!Objects need to be of a minim um size!

Objec ts need to be of amin imum size !Objectsneed to be of a minimum size!

Objectsneedtobe ofaminimum size!Objectsneedtobeofa minimum size!


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Minimum time

Minimum time for adaptation:

eyes need time to adapt to theenvironmental luminance.

Minimum time for observation:

wheels turning slowly can be

made out in detail butbecome blurred whenspinning at higher velocities.


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Perception

What we see (perceive) is not alwaysthe same as what our eyes see.

Perception is the process of

attaining awareness orunderstanding of sensory

information. What one perceives isa result of interplays between past

experiences, including onesculture, and the interpretation of

the perceived.


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Perception

What was wrongwith the previouspicture?


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Perception


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Perception

Are dots in themiddle of the

same size?


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Perception

Are these twodots of the

same size?


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Perception


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Perception

Whysome

picturesremindus on

faces?


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Perception

Will the man inthe middle

jump into thepool or ?


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Perception

Which of thesewheels is

turning left andwhich right?


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Perception

Spirals or ?


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Perception

Where is themissingsquare?


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Perceptual constancy

There are several types of perceptual constancies in Visual

perception:shape constancy,

size constancy,

color constancy,

lightness constancy,

distance constancy,

location constancy.

Color constancy means perceiving a color as "constantunder changing conditions of illumination" and is theachievement of a very complicated "calculation" by an

unconsciously working apparatus within our centralnervous system.


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Color constancy

Everybody knowsthat this mug has

just one color. It justlooks differentbecause of light

and shadow.


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Color constancy

But what aboutthese two orangedots? are their

colorssame ordifferent?


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Color constancy


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Light helps at work

Good light(ing) can bring greaterproductivity, quality and safety.


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But not always

In some cases light might be disturbing.

Disturbing effects of light


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g g

glare

Glare is caused by a significant ratio of luminance

between the task or surrounding and the glare source.

Glare can be divided

into two types: discomfort glare,

disability glare.

Discomfort glare results in an instinctive desire to look away from a brightlight source or difficulty in seeing a task. Disability glare renders the task

impossible to view, such as when driving westward at sunset.



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g g

glare

Glare is caused by the inter-reflection of light within the

eyeball, reducing the contrast between task and glaresource to the point where the task cannot be distinguished.Glare can be so intense that vision is completely impaired.

visible

not-visible



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g g

reflected glare

Reflected glare causes the same kind ofdisturbance as direct glare - reduces thecontrasts needed for trouble-free vision.



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shadows

Light and shadow are vital to ensure that objects, surfaces and

structures are clearly identifiable - shadows make it easier todetect 3D objects. However, within deep shadows with hard

edgeseverything becomes unrecognizable; even potentiallydangerous optical illusions can occur



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double light

Double-light is when we place two

spatially separated sources withdifferent colors of light in a room.In such case the appearance of

the object and the shadowdepends on the current positionand orientation of the object in

space so eyes need to adapt and

accommodate to each position.Double light can causes fatigue,

burning eyes and headaches.



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flashing light

If the intensity of the light is not constant, butlight is flashing, it can cause similar

problems as a double light. In addition,there might be a stroboscopic effect,

which prevents thecorrect perception

of moving or rotating

objects.


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I hope you remembered:

More than 80 % of information from theenvironment come through the vision!

No light no vision!

Four minimum requirements need to bemet to permit perception: minimumluminance, contrast, size and time!

Good lighting can help, bad lightingmight be disturbing!


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and now:

Questions?

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1 Visual Efects of Light