Mesopic vision models and their application

János Schanda1 and Agnes Vidovszky-Nemeth2

1. Virtual Environments and Imaging Technologies Laboratory, University of Pannonia, Hungary2. National Transport Authority, Hungary

Overview Mesopic vision fundamentals The five photosensitive cells in the human retina Luminance type and brightness type description CIE Supplementary System of Photometry, Publ.

200 CIE Recommended System for Mesopic

Photometry based on Visual Performance, Publ. 191

Examples of application and open questions

Luminance levels

Mesopic vision

Classical interpretation Daylight: photopic –

cones Dark adaptation:

scotopic – rods Twilight vision:

mesopic – cones + rods

Present day knowledge Foveal vision:

photopic Pupil diameter:

intrinsically photosensitive Retinal Ganglion Cells (ipRGC)?

Difference between perception and detection

Spectral responsivity of light sensitive cells in the human retina

5

3 types of cones, rods and ipRGCs (Cirk.-Gall)

0

0.2

0.4

0.6

0.8

1

1.2

350 400 450 500 550 600 650 700 750 800

rel.

units

wavelength, nm

Cirk-Gall

V'(λ)

L(λ)

M(λ)

S(λ)

Perception and detection Perception:

seeing details, perceiving brightness

all 3 cone types & rods

+ ipRGC (?) slower

Detection: only L & M cones

+ rodsluminance like signal

fast

Mesopic: rod contribution

Two pathways for rod-cone interaction Classical: via rod

bipolar (RB) and amacrine (RA) cells to cone bipolars (DCB & HCB)

Direct pathway via gap junctions

From Buck SL: Rod-cone interaction in human vision, The visual neuroscience

Early investigations Fovea: only cones

Luminance like: rapid, contrast

Brightness + colour: slower mechanism

Peripheric vision: rods + cones In mesopic the

influence of rods increases

Abramov-Gordon

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

400 500 600 700

wavelength, nm

log.

sen

sitiv

ity 5', foveal

1.5°, foveal

1.5°, Exc.:45°

6.5°, Exc.:45°

Stiles-Crawford (1935)

1.5

2

2.5

3

3.5

4

4.5

5

400 500 600 700

wavelength, nm

log.

rel.

sens

itivi

ty

foveal

Exc.: 5°

Early investigations Brightness

description: Kokoschka 3 conew +

rods Sagawa brightness

model Contrast threshold

investigationsNon-linear!

Reaction time based models aV(l)+(1-a)V’(l)

Brightness perception

Observation Coloured lights

brighter that white (or yellow)

Influence of S cones Rods, even in

daylight ipRGC,

responsible also for the circadian rhythm

CIE supplementary system of photometry, CIE 200:2011 for

equivalent luminance

System for brightness description in the photopic, mesopic, scotopic region

Helm holtz-Kohlrauscheffect

Purkinje effect

Equivalent luminance, Leq

a = 0.05 cd/m2, b = 2.24 cd/m2, k = 1.3, f(x,y)=Nakano (1999)Parameters:

a =L + a

L

(adaptation coefficient; achromatic)

Photopic luminance

L

Scotopicluminance

L'

(L') · (L) ·101-a a cac =

L1/2 + bkL1/2

(adaptation coefficient; chromatic)

c =ac · f(x,y)

Cr/gCy/b

Scotopic system Photopic systemV'(λ )input z(λ )inputy(λ )inputx(λ )input

c = ac [ f(x,y) - 0.078]

Detection Traffic situation

Detecting the presence of an obstacle Rapid action necessary

Can be approximated by and additive system Abney’s law holds photometry

possible Should have smooth transition to

photopic and scotopic at the two ends.

Forerunner mesopic models

Lighting Research Center of North America system:

with 0,001 cd/m2 < Lmes < 0,6 cd/m2

MOVE model, based on Ability to detect target Speed of detection Ability to identify details of target

with soft transition to scotopic and photopic at 0,01 cd/m2 < Lmes < 10 cd/m2

Comparing the two systems

Two lamps with S/P ratio: 0.65 and 1.65: difference of mesopic lum. to photopic lum. in the two systems

CIE Recommended System for Mesopic Photometry based on

Visual Performance CIE Publ 191, prepared by TC 1-58, 1

Compromise solution between the two experimental systems, main input data: achromatic contrast reaction time (see

ball in windshield of virtual reality simulation)

CIE 191, Part 2 The system is not for visual performance :

if chromatic channel signals are important: if target has narrow band spectral power distributions if brightness evaluation is required

Mesopic limits: 0,005 cd/m2 < Lmes < 5 cd/m2

The CIE 191 system is for adaptation luminance, i.e. background luminance, not for calculating mesopic luminance of target

Foveal vision is photopic!

Calculating mesopic luminance, 1

Photopic luminance Scotopic luminance

Mesopic luminance:

780nm

v e380nm

683 ( )dL L Vl l l 780nm

v e380nm

1700 '( )dL L Vl l l

whereand Vmes(l0)=Vmes(555nm)

m =1 if Lmes>5.0 cd/m2

m =0 if Lmes<0.005 cd/m2

M(m) is a normalizing constant: Vmes,max=1

Calculating mesopic luminance, 2

m is calculated using iteration Start with m0=0.5 Calculate Lmes,n from Lmes, n-1:

where

Vmes at different m values

An often encountred mistake

One often encountered picture with title „spectral sensitivity”, it is a photometry artefact: at 555 nm K(l) and K’(l) have to be equal: 683 lm/W

Spectral luminous efficacy

One could define the candela at an other wavelength, e.g 528 nm

Calculation from pavement illuminance

Input data: Photopic luminance:

Lp Luminance

coefficient of road surface (q=L /E )

S/P ratio of light source, where

780nm

380nm

1700 ( ) '( )dS S Vl l l 780nm

380nm

683 ( ) ( )dP S Vl l l and S(l) is the rel.sp. power distribution (SPD) of the lamp to be used

Calculation from pavement illuminance

Calculate Lp=qE Calculate S /P and

with Lp determine Ls:

S / P = Ls / Lp Calculate Lmes,1

fromwith m0=0.5

And do the iteration, usually 5 to 10 iterations are needed to get final Lmes

If Vmes is required

Some examples q= 0.0016 and q= 0.032 Typical light source

S/P values:S/P

LPS 0,25HPS 0,75

LED-2700K 1,12

LED-4000K 1,91

Numeric evaluation

Problems with the application of the new mesopic photometry

What is adaptation luminance? Elderly observer Visual acuity – contrast -eccentricity Effect of radiation with short

wavelength radiation Foveal vision photopic

Bodrogi: CIE mesopic Workshop, 2012.

There should be enough mesopic contrast.But to what do we adapt in this situation?

Visual field – adaptation field?

What will be the adaptation luminance?

Different sources in the visual field, different S/P ratios

Fixed Illumi-nation

Car head-lamp

Blattner: CIE Mesopic Workshop 2012

Elderly observer Change of ocular transmission with age, normalized to the 30 years old

observer

Alferdinck: CIE Mesopic Workshop 2012

Visual acuity and lamp spectrum

Test with cool-white and warm-white LEDs Young observers: < 30 years of age Old observers: > 65 years of age Reading Snellen table at 0.1 cd/m2 and 1 cd/m2

Visual acuity and lamp spectrum, results

Young observers have less errors at 0,1 cd/m2 under CW-LED

At 1 cd/m2 the difference is not significant

Visual acuity - eccentricity For a given visual acuity the

needed contrast is colour dependent and increases with excentricity

Völker: CIE Mesopic Workshop 2012

• Change of visual acuity with adaptation luminance

Further problems Re-adaptation from bright

surrounding to dark is long, increases with age

In foggy wheather light scatttering at shorter wavelength increases.

Insects sensitivity to short wavelength is higher

Astrological observations are more sensitive to short wavelength stray light

Summary The mesopic photometry model is valid for

background adaptation luminance It refers to reaction time type of tasks, not

brightness For foveal vision V(l) based metric (photopic

photometry) is valid! It is an experimental model for trial, has to be

validated with real street lighting tests and accident simulations

In preparing new recommendations spectral vision differences between young and old observers should be considered

Thanks for your kind attention!

This publication has been supported by the TÁMOP-4.2.2/B-10/1-2010-0025 project.