CORM 2012 Annual Conference and Business Meeting May 29–June 1, 2012 NRC Ottawa, Ontario An Experimental Approach to a Definition of the Mesopic Adaptation Field Tatsukiyo Uchida*, Yoshi Ohno** *Panasonic Corporation / NIST **NIST What is Mesopic Vision? 2
Mesopic vision is a visual condition where both the rods and cones contribute to vision - Most street lighting scenarios are in the mesopic range
Photopic Vision Mesopic Vision Scotopic Vision Cone Cones & Rods Rods
V(λ) Vmes(λ) V’(λ) Daylight, Interior Lighting Outdoor Lighting Darkness, Moonlight > 5cd/m2 5cd/m2 - 0.005cd/m2 < 0.005cd/m2
Spectral luminous efficiency shifts to blue range (Prukinje Effect) - Blue-rich LEDs have a potential advantage CIE 191 Mesopic Photometry System and A Remaining Issue 3
CIE 191 defines Vmes(λ) – The shape depends on parameter m derived from photopic and scotopic luminance of an adaptation field – But the adaptation field has NOT been defined 1800 1600 Km'⋅V '(λ) 1400 Photopic Luminance
λ) 1200 Kmes ⋅Vmes(λ) K'( ),
λ 1000 (
mes 800 Scotopic Luminance K 600 K ⋅V (λ) (λ), K 400 200 0 380 430 480 530 580 630 680 730 780 wavelength(nm)
Adaptation Field How big? What shape? Adaptation field – Global or Local? 4 Suitable instrument architecture depends on the adaptation mechanism Global adaptation is dominant Local adaptation is dominant
Adaptation Field
Illuminance meter type Luminance meter type is better is better
How surround luminance affect peripheral task performance? Psychophysical Experiments for the mesopic adaptation field 5 To address the Global/Local Issue, we measured detection thresholds at a peripheral point at some adaptation conditions Experimental set up 6 A computer controlled flat panel display is employed to present stimuli Set Up Layout Spectral Distribution
1.0 FPD(Screen Size: 60deg. x 40deg.) 0.9 0.8 Blue 0.7 Red 0.6 PC 0.5 0.4 0.3
55cm mouse radiance relative ND filter 0.2 0.1 0.0 chin rest 350 400 450 500 550 600 650 700 750 800 wavelength(nm)
S/P ratio Blue: 10.9 Red: 0.26 subject darkroom Adaptation conditions 7 Detection thresholds at four adaptation conditions were compared A B C D Circle Uniform Circle Circle 2 2 2 2 0.42cd/m 0.42cd/m 2.1cd/m La=Lb=2.1cd/m Adaptation 5min.
2 2 2 2 Adaptation Lum. La = 0.42cd/m La = 0.42cd/m La = 2.1cd/m La = 2.1cd/m
Task 0.6sec.
2 2 2 2 Background Lum. Lb = 0.42cd/m Lb = 0.42cd/m Lb = 0.42cd/m Lb = 2.1cd/m
Theoretical Adaptation Luminance Lta Local hypothesis 0.42cd/m2 0.42cd/m2 2.1cd/m2 - Global hypothesis 0.084cd/m2 0.42cd/m2 0.42cd/m2 - Result: Average thresholds of all subjects 8 Experiment results support the local adaptation hypothesis
0.140 Blue-Uniform 0.120 A C Blue-Circle 0.100 Blue-Circle 0.080 La=Lb=2.1cd/m2 0.060 Red-Uniform contrast ratio contrast 0.040 Red-Circle
0.020 D Red-Circle B La=Lb=2.1cd/m2 0.000 0.25 2.50 2 adaptation luminance La(cd/m ) Condition B thresholds are nearly equal to Condition A Result: Average thresholds normalized with condition A threshold 9 Condition B results strongly correlate with Condition A
1.800 Blue-Uniform 1.600
A C Blue-Circle 1.400
1.200 Blue-Circle 1.000 La=Lb=2.1cd/m2 0.800 Red-Uniform 0.600 Red-Circle relative ratio relative contrast 0.400
0.200 B D Red-Circle La=Lb=2.1cd/m2 0.000 0.25 2.50 2 adaptation luminance La(cd/m ) Result: measured threshold structure 10 Red thresholds are more ‘linear’ than Blue Red Blue 0.100 0.100 2 La = 2.1cd/m 0.090 2 0.090 La = 1.23cd/m 0.080 L = 0.72cd/m2 C 0.080 a C 0.070 0.070 2 0.060 La = 0.42cd/m 0.060
0.050 A 0.050 A 0.040 0.040 contrast ratio contrast contrast ratio contrast D 0.030 Lb=2.1cd/m2 D 0.030 Lb=2.1cd/m2 0.020 Lb=1.23cd/m2 0.020 Lb=1.23cd/m2 Lb=0.72cd/m2 Lb=0.72cd/m2 0.010 0.010 Lb=0.42cd/m2 Lb=0.42cd/m2 0.000 0.000 0.250 2.500 0.250 2.500 2 2 adaptation luminance La(cd/m ) adaptation luminance La(cd/m ) Stimuli pattern: Circle Number of subject: 1 Red result is more appropriate to see the effect of surround luminance Adaptation luminance derived from the Red experiment result 11 Condition B threshold is significantly higher than Condition A – There is small effect by surround luminance
0.140
0.120 C 0.100 Significant level 5% B 0.080 *
0.060 A contrast ratio contrast 0.040 Red-Uniform Red-Circle 0.020
0.000 2 2 0.25 0.42cd/m 0.54cd/m 2.50 2 adaptation luminance La(cd/m ) A hypothesis of the peripheral adaptation luminance 12 If rods and cones activities depend on local luminance mainly, we can apply the same idea as fovea to peripheral adaptation luminance Equivalent Model veiling luminance La, peripheral = Lperipheral + Lv Lv line of sight peripheral La, peripheral L Luminance at a Adaptation luminance peripheral task of a peripheral task point point
Candidate methods for adaptation luminance estimation
1. La, peripheral = Lperipheral, ave + Lv (CIE General Disability Glare Equation)
2. La, peripheral = Lperipheral, ave + Lv (Stiles-Holladay Disability Glare formula)
3. La, peripheral = Lperipheral, ave (Neglecting veiling luminance) Can we determine adaptation luminance with candidate methods? 13
Lperipheral and Lperipheral+Lv (CIE General Disability Glare Equation) can estimate adaptation luminance with small error of mesopic target luminance Adaptation and target luminance estimated with the candidate methods 2 photopic adaptation luminance mesopic target luminance Lmes,t(cd/m ) 2 2 2 2 method Lp,a(cd/m ) error Lp,t=0.5cd/m Lp,t=1.0cd/m Lp,t=2.0cd/m error experiment 0.54 - 0.44 0.87 1.75 - 1. L +L peripheral v 0.48 12.4% 0.43 0.86 1.73 1.1% (CIE General Equ.) 2. L +L peripheral v 1.28 135.2% 0.46 0.93 1.86 6.5% (Stiles-Holladay)
3. Lperipheral 0.42 22.6% 0.43 0.85 1.71 2.2% Photopic adaptation luminance error is large, but mesopic target luminance error is small Adaptation field based on the local adaptation hypothesis 14 Adaptation field should depend on eye-fixation = application dependent
Could be different between observers even in same scenario Practical methods for mesopic luminance / M/P ratio measurement 15 Shouldn’t employ special optics for each adaptation field – too many optical attachments! Imaging luminance meter Spot luminance meter Measure luminance image by one Measure luminance at point-by-point shot Realize an adaptation field by Realize adaptation fields by image definition of a measurement points processing (mask pattern) set
Small geometry error Large geometry error Large spectral mismatch Very small spectral mismatch when – glass filters are necessary employ spectrometer A option for the spot mesopic luminance meter 16 SiPD array colorimeter is useful as a base of the mesopic luminance meter and M/P ratio meter Employ 40 channels SiPD array to realize various spectral responsivity without filters
Easy to realize V(λ) & V’(λ) Can measure low level luminance quickly Low cost than spectrometer Portable – buttery powered & lightweight
(Shimizu et al. KONICA MINOLTA Technology Report vol.2, 2006) Usage of mesopic luminance meter 17 Easy to correct illuminance values measured by existing illuminance meters
Mesopic luminance measurement Mesopic Mesopic Luminance Meter Luminance M/P ratio Photopic Luminance Scotopic Luminance Mesopic illuminance measurement M/P ratio meter (= Mesopic Luminance Meter) Existing Illuminance meter M/P ratio Mesopic Illuminance
Photopic Illuminance Conclusions and Further Issues 18 Conclusions Adaptation luminance mainly depends on local luminance Adaptation fields can be defined from • Critical task points • Eye-fixation – These depend on application Imaging luminance meter or spot luminance meter should be employed to avoid too many special optics for each adaptation field
Further Issues Correct luminance distribution samples at street lighting scenarios – to estimate geometry error and effect of veiling luminance Compare 2 types of instrument – Imaging luminance meter / Spot luminance meter Acknowledgement 19
This research is funded by NEDO. Thank you for your attention [email protected] Past Studies about adaptation luminance of fovea 21 Fovea cells adapt to sum of center luminance and veiling luminance when adapted to the wide field of view luminance distribution (Holladay 1926, Crawford 1936, Moon & Spencer 1943, Fry et al. 1963, CIE 146:2002)
Basic idea Equivalent veiling luminance Luminance at the fovea caused by light Equivalent veiling luminance coming from peripheral field of view and Lv scattered in eyes c L 0.35 0.30 Center Luminance 0.25 La, fovea 0.20 Adaptation luminance 0.15 of fovea 0.10
coefficent of E(lx) of coefficent 0.05 0.00 0 20 40 60 80 Angle of arc between the line of sight and a La, fovea = Lc + Lv glare source(degree) A definition of adaptation luminance in CIE Publications 22 Definition of threshold increment TI defined an average luminance of road surface as the center luminance (CIE 115:2010, CIE 140:2000, CIE 150:2003) Lv Equivalent veiling luminance
La, fovea Lc, ave Adaptation luminance average luminance of fovea of road surface La, fovea = Lc + Lv
Since the line of sight scans everywhere road surface Lc = Lc, ave La, fovea = Lc, ave + Lv
If luminance of peripheral field of view is low enough Lv << Lc, ave La, fovea ≈ Lc, ave Procedure 23 Random Staircase Method was employed for threshold measurement Measurement Method : Random Staircase Method
Time Table Randomized
Circle Circle Uniform Circle 2 2 2 2 Pre- 0.42cd/m 2.1cd/m 0.42cd/m La= Lb=2.1cd/m Adapt Adapt Tasks Adapt Tasks Adapt Tasks Adapt Tasks
more than 5min. 5min. 5min. 5min. 5min. ) 2 1st Trial 2nd Trial La Present target Lb
Target Position Target Lt Luminance(cd/m 0.2 0.2 0.2 5sec. after Time(sec) subject responds Pattern of stimuli 24 Use “Uniform” and “Circle” pattern to see surround luminance effect
“Uniform” pattern “Circle” pattern Fixation point
60deg.
40deg. 10deg.
12.4deg.
Target(diameter=1deg.) Task To respond whether the subject saw a target or not The area of circle is 1/5 of full screen Subjects 25 11 subjects with normal vision took part in the experiment Number of Subject: 11 Age: 30 – 68 (30’s: 4, 40’s: 5, 60’s:2) (Corrected) Visual Acuity: 0.5 – 1.3 (10/20 – 20/15) Normal Color Vision Expected threshold structure based on CIE 191 26 Higher S/P ratio condition should have steeper threshold slope when background luminance is constant
L =L L =constant a b b Lb=L1
Lb=L2
Lb=L3 ratio contrast Lb=L4
low high S/P ratio
L1 L2 L3 L4 2 adaptation luminance La(cd/m ) Another experiment was conducted to confirm the threshold structure Mesopic Photometry System Recommended in CIE191 27
CIE 191 defined the mesopic spectral luminous efficiency Vmes(λ) as a simple combination of V(λ) and V’(λ) 1800 1600 Km'⋅V '(λ) 1400
λ) 1200 Kmes ⋅Vmes(λ) K'( ),
λ 1000 (
mes 800 K 600 K ⋅V (λ) (λ), K 400 200 0 380 430 480 530 580 630 680 730 780 wavelength(nm)
Vmes(λ) shape depends on parameter m
M (m)Vmes(λ) = mV (λ) + (1− m)V '(λ) for 0 ≤ mn ≤1 683 Lmes = ∫Vmes(λ)Le(λ)dλ : Mesopic Luminance Vmes(λ 0)
Vmes(λ) :mesopic spectral sensitivity Lmes :mesopic luminance Vmes(λ 0) :the value of Vmes(λ) at 555nm -2 -1 -1 M (m) :a noromalizing function such that Vmes(λ) attains a maximum value of 1 Le(λ) : spectral radiance in Wm sr m A Problem to be solved to apply CIE 191 to lighting applications 28
The coefficient m is calculated from the photopic and scotopic luminance of an adaptation field - But the adaptation field has NOT been defined
Calculated using iterative approach
:the photopic luminance of the adaptation field NOT Defined! :the scotopic luminance of the adaptation field
:683/1699 is the value of scotopic spectral luminous efficiency function
at λ0 =555nm :parameter(=0.7670) :parameter(=0.3334)
The value of Lmes obtained by the equations above is the mesopic luminance of the visual adaptation field. The mesopic luminance of objects in the visual adaptation field is obtained according to equations (2) and (3) using the value of m determined for the adaptation field. - CIE 191:2010 Equations for Disability Glare 29
CIE General Disability Glare Equation
π 4 2π 2 10 5 0.1p A Lv = E(θ,φ) + + ⋅ 1+ + 0.0025pdθdφ ∫0 ∫0 3 2 θ θ θ 62.5 ：eye pigmentation factor (0=black, 0.5=brown, 1.0=light eyes, 1.2=very light-blue eyes) ：Age in years
Stiles-Holladay Disability Glare formula
π 2π 2 10 v = θ φ θ φ L E( , ) 2 d d ∫0 ∫0 θ