mesopic vision models and their application
DESCRIPTION
Mesopic vision models and their application. János Schanda 1 and Agnes Vidovszky-Nemeth 2 1. Virtual Environments and Imaging Technologies Laboratory, University of Pannonia, Hungary 2. National Transport Authority, Hungary. Overview. Mesopic vision fundamentals - PowerPoint PPT PresentationTRANSCRIPT
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.