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 Mesopic vision fundamentals The five photosensitive cells in the human retina The five photosensitive cells in the human retina Luminance type and brightness type description Luminance type and brightness type description CIE Supplementary System of Photometry, Publ. 200 CIE Supplementary System of Photometry, Publ. 200 CIE Recommended System for Mesopic Photometry based on Visual Performance, Publ. 191 CIE Recommended System for Mesopic Photometry based on Visual Performance, Publ. 191 Examples of application and open questions Examples of application and open questions

Luminance levels

Mesopic vision Classical interpretation Classical interpretation Daylight: photopic – cones Daylight: photopic – cones Dark adaptation: scotopic – rods Dark adaptation: scotopic – rods Twilight vision: mesopic – cones + rods Twilight vision: mesopic – cones + rods Present day knowledge Present day knowledge Foveal vision: photopic Foveal vision: photopic Pupil diameter: intrinsically photosensitive Retinal Ganglion Cells (ipRGC)? Pupil diameter: intrinsically photosensitive Retinal Ganglion Cells (ipRGC)? Difference between perception and detection 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)

Perception and detection Perception: Perception: seeing details, perceiving brightness seeing details, perceiving brightness all 3 cone types & rods all 3 cone types & rods + ipRGC (?) + ipRGC (?) slower slower Detection: Detection: only L & M cones + rods luminance like signal only L & M cones + rods luminance like signal fast fast

Mesopic: rod contribution Two pathways for rod- cone interaction Two pathways for rod- cone interaction Classical: via rod bipolar (RB) and amacrine (RA) cells to cone bipolars (DCB & HCB) Classical: via rod bipolar (RB) and amacrine (RA) cells to cone bipolars (DCB & HCB) Direct pathway via gap junctions Direct pathway via gap junctions From Buck SL: Rod-cone interaction in human vision, The visual neuroscience

Early investigations Fovea: only cones Fovea: only cones Luminance like: rapid, contrast Luminance like: rapid, contrast Brightness + colour: slower mechanism Brightness + colour: slower mechanism Peripheric vision: rods + cones Peripheric vision: rods + cones In mesopic the influence of rods increases In mesopic the influence of rods increases

Early investigations Brightness description: Brightness description: Kokoschka 3 conew + rods Kokoschka 3 conew + rods Sagawa brightness model Sagawa brightness model Contrast threshold investigations Contrast threshold investigationsNon-linear! Reaction time based models Reaction time based models aV( )+(1-a)V’( ) aV( )+(1-a)V’( )

Brightness perception Observation Observation Coloured lights brighter that white (or yellow) Coloured lights brighter that white (or yellow) Influence of Influence of S cones S cones Rods, even in daylight Rods, even in daylight ipRGC, responsible also for the circadian rhythm ipRGC, responsible also for the circadian rhythm

CIE supplementary system of photometry, CIE 200:2011 for equivalent luminance System for brightness description in the System for brightness description in the photopic, mesopic, scotopic region photopic, mesopic, scotopic region

Detection Traffic situation Traffic situation Detecting the presence of an obstacle Detecting the presence of an obstacle Rapid action necessary Rapid action necessary Can be approximated by and additive system Can be approximated by and additive system Abney’s law holds photometry possible Abney’s law holds photometry possible Should have smooth transition to photopic and scotopic at the two ends. Should have smooth transition to photopic and scotopic at the two ends.

Forerunner mesopic models Lighting Research Center of North America system: Lighting Research Center of North America system: with 0,001 cd/m 2 < L mes < 0,6 cd/m 2 with 0,001 cd/m 2 < L mes < 0,6 cd/m 2 MOVE model, based on MOVE model, based on Ability to detect target Ability to detect target Speed of detection Speed of detection Ability to identify details of target Ability to identify details of target with soft transition to scotopic and photopic at 0,01 cd/m 2 < L mes < 10 cd/m 2 0,01 cd/m 2 < L mes < 10 cd/m 2

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: Compromise solution between the two experimental systems, main input data: achromatic contrast achromatic contrast reaction time (see ball in windshield of virtual reality simulation) reaction time (see ball in windshield of virtual reality simulation)

CIE 191, Part 2 The system is not for visual performance : The system is not for visual performance : if chromatic channel signals are important: if chromatic channel signals are important: if target has narrow band spectral power distributions if target has narrow band spectral power distributions if brightness evaluation is required if brightness evaluation is required Mesopic limits: 0,005 cd/m 2 < L mes < 5 cd/m 2 Mesopic limits: 0,005 cd/m 2 < L mes < 5 cd/m 2 The CIE 191 system is for adaptation luminance, i.e. background luminance, not for calculating mesopic luminance of target The CIE 191 system is for adaptation luminance, i.e. background luminance, not for calculating mesopic luminance of target Foveal vision is photopic! Foveal vision is photopic!

Calculating mesopic luminance, 1 Photopic luminance Scotopic luminance Photopic luminance Scotopic luminance Mesopic luminance: Mesopic luminance: whereand V mes ( 0 )=V mes (555nm) m =1 if L mes >5.0 cd/m 2 m =0 if L mes <0.005 cd/m 2 M(m) is a normalizing constant: V mes,max =1

Calculating mesopic luminance, 2 m is calculated using iteration m is calculated using iteration Start with m 0 =0.5 Start with m 0 =0.5 Calculate L mes,n from L mes, n-1 : Calculate L mes,n from L mes, n-1 : where

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

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

Calculation from pavement illuminance Input data: Input data: Photopic luminance: L p Photopic luminance: L p Luminance coefficient of road surface (q=L /E ) Luminance coefficient of road surface (q=L /E ) S/P ratio of light source, where S/P ratio of light source, where and S( ) is the rel.sp. power distribution (SPD) of the lamp to be used

Calculation from pavement illuminance Calculate L p =qE Calculate L p =qE Calculate S /P and with L p determine L s : Calculate S /P and with L p determine L s : S / P = L s / L p S / P = L s / L p Calculate L mes,1 from with m 0 =0.5 Calculate L mes,1 from with m 0 =0.5 And do the iteration, usually 5 to 10 iterations are needed to get final L mes And do the iteration, usually 5 to 10 iterations are needed to get final L mes If V mes is required If V mes is required

Some examples q= and q= and q= q= Typical light source S/P values: Typical light source S/P values: S/P LPS0,25 HPS0,75 LED-2700K1,12 LED-4000K1,91

Numeric evaluation

Problems with the application of the new mesopic photometry What is adaptation luminance? What is adaptation luminance? Elderly observer Elderly observer Visual acuity – contrast -eccentricity Visual acuity – contrast -eccentricity Effect of radiation with short wavelength radiation Effect of radiation with short wavelength radiation Foveal vision photopic Foveal vision photopic

Bodrogi: CIE mesopic Workshop, 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 FixedIllumi-nation Carhead-lamp Blattner: CIE Mesopic Workshop 2012

Elderly observer Change of ocular transmission with age, normalized to the 30 years old 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 Test with cool-white and warm-white LEDs Young observers: < 30 years of age Young observers: < 30 years of age Old observers: > 65 years of age Old observers: > 65 years of age Reading Snellen table at 0.1 cd/m 2 and 1 cd/m 2 Reading Snellen table at 0.1 cd/m 2 and 1 cd/m 2

Visual acuity and lamp spectrum, results Young observers have less errors at 0,1 cd/m 2 under CW-LED Young observers have less errors at 0,1 cd/m 2 under CW-LED At 1 cd/m 2 the difference is not significant At 1 cd/m 2 the difference is not significant

Visual acuity - eccentricity For a given visual acuity the needed contrast is colour dependent and increases with excentricity 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 Change of visual acuity with adaptation luminance

Further problems Re-adaptation from bright surrounding to dark is long, increases with age Re-adaptation from bright surrounding to dark is long, increases with age In foggy wheather light scatttering at shorter wavelength increases. In foggy wheather light scatttering at shorter wavelength increases. Insects sensitivity to short wavelength is higher Insects sensitivity to short wavelength is higher Astrological observations are more sensitive to short wavelength stray light Astrological observations are more sensitive to short wavelength stray light

Summary The mesopic photometry model is valid for background adaptation luminance The mesopic photometry model is valid for background adaptation luminance It refers to reaction time type of tasks, not brightness It refers to reaction time type of tasks, not brightness For foveal vision V( ) based metric (photopic photometry) is valid! For foveal vision V( ) 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 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 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/ project.