Mesopic vision model and its

application

János Schanda Virtual Environments and Imaging

Technologies Laboratory

University of Pannonia

Overview

Mesopic vision fundamentals The five photosensitive cells in the

human retina Luminance type and brightness type

description The CIE TC 1-69 mesopic model Examples of application

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

wavelength, nm

rel.

un

its

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

Colour perception

Historic overview

The two stumbling blocks of mesopic photometry: Purkinje shift

rod and cone interaction transition from cone to rod sp.resp. differs

from Purkinje shift Helmhotz-Kohlrausch effect

difference between luminance and brightness

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

. se

nsi

tivi

ty

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

. re

l. s

ensi

tivi

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)

Spectral responsivity at

different luminance levels Walters & Wright :

Proc. Roy. Soc. 1943.

At low mesopic levels first a shoulder is found at longer wavelength

At mid-mesopic a transition from rod to cone takes place: broadening of curve

At high mesopic narrowing to V(l) is found

Spectral responsivity at different luminance levels

Kinney clearly identifies in 1955 that at high mesopic and photopic levels brightness sensitivity has a multi bump nature

CIE 1963 mesopic spectral sensitivities

400 450 500 550 600 650 7000

0.2

0.4

0.6

0.8

1

10-5 cd/m210-3 cd/m210-1 cd/m210 cd/m2

wavelength, nm

rel.

Sen

siti

vit

y

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

Quantitative descriptions of mesopic luminance

Equivalent luminance (CIE 1963):„The equivalent luminance of the field of an arbitrary spectral composition is the standard luminance of another field which has the colour temperature of 2042 K and which in particular photometric conditions seems to be equally bright to the first field.”

Mesopic 2 function brightness scale

Palmer (1966, 1967, 1968): Equivalent luminance (L) for large fields L(S,P)=(MS+P 2)/(M+P)where:

S: scotopic value P: photopic (10°) value M parameter, 6.28 . 10-2 cd/m2 for 15° field

Other models used direct cone brightness functions (e.g. Ikeda & Shimozono, 1981; Nakano & Ikeda, 1986; Sagawa & Takeichi, 1983; modified Palmer formula)

Mesopic 4 function brightness

Helmhotz-Kohlrausch effect: brightness non-additivity, influence of all three cone types Kokoschka model Trezona – Clarke model Problem of transition between

luminance type (photopic) and brightness type (scotopic) experimental data: Viénot et al.

Kokoschka model

10 10eq 10

10 10 10x y z S

X Z SL F F F F L

Y Y L

where Fx, Fy, Fz functions depend on luminance level, L10 is photopic 10°luminance S is scotopic luminance X10, Y10, Z10 are 10° tristimulus values

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

Kokoschka model functions and derived spectral luminous efficiency functions

Brightness/luminance discrepancy & rod/cone interaction + ipRGCs

1. In photopic regime one assumes: luminance to be a combination of the L-

and M-cone signals Brightness to be a combination of all

three cone signals after a transformation into magno-, parvo- and conio-cellular signals

2. In mesopic regime rod contribution has to be added.

3. Recently found ipRGCs have influence on pupillary reflex, influencing light reaching the retina

Photopic regime: brightness/luminance

Magnocellular pathway: luminance like

Brightness: all 3 channels

B=(L2+d2+t2)1/2

(Guth model) Influence of

ipRGCs?Different brightness of metameric samples

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

2 new CIE reports

CIE supplementary system of photometry, CIE 200:2011

Recommended system for mesopic photometry based on visual performance, based on MOVE and X-models

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 c

ac =L

1/2+ b

kL1/2

(adaptation coefficient; chromatic)

c =ac · f(x,y)

Cr/gCy/b

Scotopic system Photopic system

V'(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.

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 TC 1-58 system, 1

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

ball in windshield of virtual reality simulation)

CIE TC 1-58 system, 2 The system is not for visual performance :

if chromatic channel signals are important:S/P ratio very higy or low

if target has narrow band spectral power distributions if brightness evaluation is required

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

The TC 1-58 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 e

380nm

683 ( )dL L V 780nm

v e

380nm

1700 '( )dL L V

where

and 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

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 V 780nm

380nm

683 ( ) ( )dP S V 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

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, used

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

S/P values:

S/PLPS 0,25

HPS 0,75

LED-2700K 1,12

LED-4000K 1,91

Numeric evaluation

Visual acuity and lamp spectrum

Transmission of eye media changes with age 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

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

Peter Kaisers vision of the future photometer in 1981

Modern image taking photometers are almost there

+ info:

background ipRGCs