An Experimental Approach to a Definition of the Mesopic Adaptation Field

Transcription

1 May 29 June 1, 2012 NRC Ottawa, Ontario CORM 2012 Annual Conference and Business Meeting An Experimental Approach to a Definition of the Mesopic Adaptation Field Tatsukiyo Uchida*, Yoshi Ohno** *Panasonic Corporation / NIST **NIST

2 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 Cone V(λ) Daylight, Interior Lighting > 5cd/m 2 Mesopic Vision Cones & Rods V mes (λ) Outdoor Lighting 5cd/m cd/m 2 Scotopic Vision Rods V (λ) Darkness, Moonlight < 0.005cd/m 2 Spectral luminous efficiency shifts to blue range (Prukinje Effect) - Blue-rich LEDs have a potential advantage

3 CIE 191 Mesopic Photometry System and A Remaining Issue 3 CIE 191 defines V mes (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 K(λ), K mes (λ), K'(λ) ' Km V '( λ) Kmes Vmes(λ) wavelength(nm) K V (λ) Photopic Luminance Scotopic Luminance Adaptation Field How big? What shape?

4 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 is better Luminance meter type is better How surround luminance affect peripheral task performance?

5 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

6 Experimental set up 6 A computer controlled flat panel display is employed to present stimuli Set Up Layout Spectral Distribution FPD(Screen Size: 60deg. x 40deg.) ND filter chin rest 55cm mouse PC relative radiance Blue 0.7 Red wavelength(nm) subject darkroom S/P ratio Blue: 10.9 Red: 0.26

7 Adaptation conditions 7 Detection thresholds at four adaptation conditions were compared Adaptation 5min. A B C D Circle 0.42cd/m 2 Uniform 0.42cd/m 2 Circle 2.1cd/m 2 Circle L a =L b =2.1cd/m 2 Adaptation Lum. Task 0.6sec. L a = 0.42cd/m 2 L a = 0.42cd/m 2 L a = 2.1cd/m 2 L a = 2.1cd/m 2 Background Lum. L b = 0.42cd/m 2 L b = 0.42cd/m 2 L b = 0.42cd/m 2 L b = 2.1cd/m 2 Theoretical Adaptation Luminance L ta 0.42cd/m cd/m 2 2.1cd/m 2 Local hypothesis Global hypothesis 0.084cd/m cd/m cd/m 2 - -

8 Result: Average thresholds of all subjects 8 Experiment results support the local adaptation hypothesis A C Blue-Uniform Blue-Circle contrast ratio Blue-Circle La=Lb=2.1cd/m2 Red-Uniform Red-Circle B D adaptation luminance L a (cd/m 2 ) Red-Circle La=Lb=2.1cd/m2 Condition B thresholds are nearly equal to Condition A

9 Result: Average thresholds normalized with condition A threshold 9 Condition B results strongly correlate with Condition A relative contrast ratio A C B D adaptation luminance L a (cd/m 2 ) Blue-Uniform Blue-Circle Blue-Circle La=Lb=2.1cd/m2 Red-Uniform Red-Circle Red-Circle La=Lb=2.1cd/m2

10 contrast ratio Result: measured threshold structure 10 Red thresholds are more linear than Blue Red Blue L a = 0.42cd/m 2 A L a = 2.1cd/m 2 L a = 1.23cd/m 2 C L a = 0.72cd/m Lb=2.1cd/m Lb=1.23cd/m Lb=0.72cd/m2 Lb=0.42cd/m adaptation luminance L a (cd/m 2 ) D contrast ratio Lb=2.1cd/m Lb=1.23cd/m Lb=0.72cd/m2 Lb=0.42cd/m adaptation luminance L a (cd/m 2 ) Stimuli pattern: Circle Number of subject: 1 Red result is more appropriate to see the effect of surround luminance A C D

11 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 contrast ratio Significant level 5% * A B Red-Uniform Red-Circle C cd/m cd/m adaptation luminance L a (cd/m 2 )

12 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 Model L + a, peripheral = Lperipheral L v v La, Equivalent veiling luminance L peripheral Adaptation luminance of a peripheral task point line of sight Candidate methods for adaptation luminance estimation 1. L + a, peripheral = Lperipheral, ave Lv L peripheral Luminance at a peripheral task point (CIE General Disability Glare Equation) L + a, peripheral = Lperipheral, ave Lv L = a, peripheral Lperipheral, ave (Stiles-Holladay Disability Glare formula) (Neglecting veiling luminance)

13 Can we determine adaptation luminance with candidate methods? 13 L peripheral and L peripheral +L v (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 photopic adaptation luminance mesopic target luminance L mes,t (cd/m 2 ) method L p,a (cd/m 2 ) error L p,t =0.5cd/m 2 L p,t =1.0cd/m 2 L p,t =2.0cd/m 2 error experiment L peripheral +L v (CIE General Equ.) % % 2. L peripheral +L v (Stiles-Holladay) % % 3. L peripheral % % Photopic adaptation luminance error is large, but mesopic target luminance error is small

14 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

15 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 Measure luminance image by one shot Realize adaptation fields by image processing (mask pattern) Spot luminance meter Measure luminance at point-by-point Realize an adaptation field by definition of a measurement points set Small geometry error Large spectral mismatch glass filters are necessary Large geometry error Very small spectral mismatch when employ spectrometer

16 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)

17 Usage of mesopic luminance meter 17 Easy to correct illuminance values measured by existing illuminance meters Mesopic luminance measurement Mesopic Luminance Meter Mesopic illuminance measurement Existing Illuminance meter M/P ratio meter Mesopic Luminance M/P ratio Photopic Luminance Scotopic Luminance (= Mesopic Luminance Meter) M/P ratio Photopic Illuminance Mesopic Illuminance

18 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

19 Acknowledgement 19 This research is funded by NEDO.

20 Thank you for your attention

21 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) L a, Basic idea Equivalent veiling luminance fovea Lv Adaptation luminance of fovea L a, fovea = Lc + Lc Center Luminance L v coefficent of E(lx) Equivalent veiling luminance Luminance at the fovea caused by light coming from peripheral field of view and scattered in eyes Angle of arc between the line of sight and a glare source(degree)

22 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 L a, fovea Adaptation luminance of fovea L a, fovea = Lc + L v L c, ave average luminance of road surface Since the line of sight scans everywhere road surface L a, fovea = Lc, ave + If luminance of peripheral field of view is low enough L a, fovea Lc, ave L v L c = Lc, ave L v << Lc, ave

23 Procedure 23 Random Staircase Method was employed for threshold measurement Measurement Method : Random Staircase Method Time Table Randomized Pre- Adapt Adapt Circle 0.42cd/m 2 Tasks Adapt Circle 2.1cd/m 2 Tasks Adapt Uniform 0.42cd/m 2 Tasks Circle L a = L b =2.1cd/m 2 Adapt Tasks more than 5min. 5min. 5min. 5min. 5min. Target Position Luminance (cd/m 2 ) L a L b L t 1st Trial Present target 2nd Trial sec. after subject responds Time(sec)

24 Pattern of stimuli 24 Use Uniform and Circle pattern to see surround luminance effect Uniform pattern Fixation point Circle pattern 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

25 Subjects subjects with normal vision took part in the experiment Number of Subject: 11 Age: (30 s: 4, 40 s: 5, 60 s:2) (Corrected) Visual Acuity: (10/20 20/15) Normal Color Vision

26 Expected threshold structure based on CIE Higher S/P ratio condition should have steeper threshold slope when background luminance is constant L a =L b L b =constant L b =L 1 contrast ratio L b =L 2 L b =L 3 L b =L 4 low S/P ratio high L 1 L 2 L 3 L 4 adaptation luminance L a (cd/m 2 ) Another experiment was conducted to confirm the threshold structure

27 Mesopic Photometry System Recommended in CIE CIE 191 defined the mesopic spectral luminous efficiency V mes (λ) as a simple combination of V(λ) and V (λ) K(λ), K mes (λ), K'(λ) M ( m) Vmes( λ) = mv ( λ) + (1 m) V '( λ) L mes V M (m) mes(λ) '( λ) 683 = Vmes λ Le λ dλ Vmes λ ( ) ( ) ( 0) ' Km V Kmes Vmes(λ) wavelength(nm) K V (λ) V mes (λ) shape depends on parameter m :mesopic spectral sensitivity Lmes :a noromalizing function such that V mes (λ) attains a maximum value of 1 for 0 mn 1 : Mesopic Luminance :mesopic luminance ( λ 0) Le(λ) Vmes :the value of V mes (λ) at 555nm : spectral radiance in Wm -2 sr -1 m -1

28 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 :the scotopic luminance of the adaptation field NOT Defined! :683/1699 is the value of scotopic spectral luminous efficiency function at λ 0 =555nm :parameter(=0.7670) :parameter(=0.3334) The value of L mes 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

29 Equations for Disability Glare 29 φ θ θ θ θ φ θ π π d d p A p E Lv = ), ( Stiles-Holladay Disability Glare formula φ θ θ φ θ π π d d E Lv = ), ( CIE General Disability Glare Equation :eye pigmentation factor (0=black, 0.5=brown, 1.0=light eyes, 1.2=very light-blue eyes) :Age in years