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8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
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2008 Rensselaer Polytechnic Institute. All rights reserved.
Spectral and Temporal FactorsAssociated with Headlight Glare:
Implications for Measurement
John D. Bullough, Ph.D.Lighting Research Center, Rensselaer Polytechnic Institute
Council for Optical Radiation Measurements Conference
Troy, NY
June 10-11, 2008
8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
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Background
Present characterizationof vehicle headlightphotometry is based on: Photopic luminous
efficiency function
Luminous intensity valuesat specific angular locations
0
0.25
0.5
0.75
1
400 500 600 700
wavelength (nm)
r
elativevalue
SAE Low Beam Requirements
-5
0
5
10
15
-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30
horizontal angle (degrees)
verticalangle(degree
maxima
minima
road edge
center line
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3
The Perfect Storm?
In the past decade, vehicleheadlights have evolved in anumber of ways (NHTSA, 2007):
New (often "bluer") and sometimeshigher-output light sources
High-intensity discharge (HID, or xenon)
Coated-bulb halogen
Coming soon: light-emitting diode (LED)
Increased mounting heights (e.g.,SUVs)
Decreased likelihood of proper aim
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Spectral Power Distribution
The trend with newer headlight sources istoward increased short-wavelength light output
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Spatial Distribution
Because of improved luminous efficacy,HID headlamps have increased peripheral
light output
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Characterizing Headlight Glare
Disability glare
Reduction in visibility caused by luminous veil
due to scattered light in the eye Well-understood quantitatively for decades
(Fry, 1954)
Discomfort glare
Annoying or painful sensation when exposedto a bright light in the field of view
Much less understood (Rea, 2000)
8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
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Characterizing Headlight Glare
Visual recovery
Reduction in visibility caused by increased
visual adaptation followed by several secondsof reduced visual sensitivity afterexposure toa bright light
8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
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Disability Glare
Reductions in visibilityfrom oncoming headlightswith different spectral
power distributionsdepended only on thephotopic illuminance at
the eye(Bullough et al., 2003)
Conventional photometriccharacterization has utilityin predicting disability glare
780
800
820
840
860
880
900
920
0.2 1 5
oncoming illuminance (lx)
reactiontime(ms)
780
800
820
840
860
880
900
920
0.2 1 5
oncoming illuminance (lx)
reactiontime(ms)
8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
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Discomfort Glare
Mechanisms are not understood
Methods to characterize discomfort glare
physiologically have not been successful Pupil size fluctuation
Electrophysiological measures
Squinting Psychology surely plays a role, too
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The State of the Art in DiscomfortGlare
Subjective ratings De Boer (1967) scale is
common in automotivelighting research
Discomfort glare ratings arestrongly correlated withilluminance at the eye
Background light level,location in field of view, and
even what one is doing whenrating the glare all influencethe absolute level ofdiscomfort (Bullough et al., 2002,2003, in press; Theeuwes et al., 2002)
1
3
5
7
9
0.01 0.1 1 10 100
Illuminance at Eye (lx)
MeanDeBoerrating
9: Just Noticeable8:7: Satisfactory6:5: Just Acceptable4:3: Disturbing
2:1: Unbearable
9: Just Noticeable8:7: Satisfactory6:5: Just Acceptable4:3: Disturbing
2:1: Unbearable
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Discomfort Glare
Headlights with greater short-wavelength light output
produced greater discomfort (Bullough et al., 2002, 2003; Flannagan, 1999)
0
1
2
3
4
5
halogen blue-filtered halogen HID
oncoming light source
D
eBoerrating
0
1
2
3
4
5
halogen blue-filtered halogen HID
oncoming light source
D
eBoerrating
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A Possible Mechanism?
Imagine creating a luminous efficiency function from theshort-wavelength (S) cone photoreceptor spectralsensitivity
Peak near 450 nm
0
0.25
0.5
0.75
1
400 500 600 700
Wavelength (nm)
Relative
Value
Photopic
S Cone
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Further Experiments
Using narrowband filters and a xenon lightsource, discomfort glare from 5o off-axis wasmeasured for several wavelengths and several
illuminances at the eye (Dee, 2003)
450 nm 510 nm 590 nm 650 nm 700 nm
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Modeling Spectral Sensitivityfor Discomfort Glare
A combination of V10() (CIE, 2005) and short-wavelength cone sensitivity was the best rectifyingvariable for discomfort ratings
Follow-up study (Watkinson, 2005) confirmed these results
0
0.25
0.5
0.75
1
400 500 600 700
Wavelength (nm)
RelativeValue
y = -0.94Ln(x) + 4.09
R2
= 0.97
1
2
3
4
5
6
7
8
9
0.01 0.1 1 10 100
Log VDG() Illuminance
DeBoerRating
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Is Discomfort Glare ExcessBrightness?
If so, peripheralbrightness data from
Weale (1953) offer aninteresting hypothesisfor peripheral anglesother than 5o
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Role of Spatial Distribution
Disability and discomfort glare are acutephenomena
Different headlights provide differentilluminance "profiles" to oncoming drivers
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Characterizing Headlights forVisual Recovery
Dosage: illuminance duration
Peak: maximum illuminance
To what extent to these parameters impactvisual recovery?
0
0.5
1
1.5
2
2.5
3
3.5
0 0.5 1 1.5 2 2.5 3
time (s)
illuminance(lx)
"Flash" high
"Gradual" high
8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
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Recovery Laboratory Study
Four illuminance/dosage conditions: 1 lux for 5 seconds (dosage = 5 lxsec)
2 lux for 2.5 seconds (dosage = 5 lxsec)
2 lux for 5 seconds (dosage = 10 lxsec)
4 lux for 2.5 seconds (dosage = 10 lxsec)
Time to detect a target presentedimmediately after exposure profile wasmeasured (Chen, 2004)
0
0.5
1
1.52
2.5
3
3.5
4
4.5
0 1 2 3 4 5 6
Time (s)
Illumin
ance(lux)
P2.0
P2.1
P2.2
P2.3
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Recovery Laboratory Study Results
Recoverytimes werecorrelatedwith dosage
Discomfortratings were
correlatedwith peakilluminance(Chen, 2004)
y = -1.05x + 7.16
R2 = 0.99
1
2
3
45
6
7
8
9
0 1 2 3 4 5
Illuminance (lx)
DeBoer
Rating
P2.0
P2.1
P2.2
P2.3
y = 0.04x + 0.45
R
2
= 0.99
0
0.2
0.4
0.6
0.8
1
1.21.4
1.6
1.8
4 6 8 10 12
Glare Dosage (lx.s)
RecoveryTime(s)
P2.0
P2.1
P2.2
P2.3
8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
20/23 2008 Rensselaer Polytechnic Institute. All rights reserved.
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Implications for HeadlightMeasurement
Conventional headlight photometry onlypartially characterizes their glare-related
properties Disability glare
0
0.25
0.5
0.75
1
400 500 600 700
wavelength (nm)
relativevalue
8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
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Characterizing Discomfort Glare
A function combiningphotopic (large-field)sensitivity and short-
wavelength (S cone)sensitivity appears torectify discomfort glarefrom different spectra(at 5o)
0
0.25
0.5
0.75
1
400 500 600 700
Wavelength (nm)
RelativeValue
8/3/2019 Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement
22/23 2008 Rensselaer Polytechnic Institute. All rights reserved.
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Characterizing Visual Recovery
Integrated value of intensity over angles of interest mightbe a more suitable measure of potential for long recoverytimes following headlamp exposure
SAE Low Beam Requirements
-5
0
5
10
15
-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30
horizontal angle (degrees)
verticalangle(degrees)
maxima
minima
road edge
center line
oncomingdriver
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Acknowledgments
Spectral sensitivity studies
Transportation Lighting Alliance
Automotive Lighting, DaimlerChrysler, GE Lighting, General
Motors, Guide Corporation, Hella, Philips Lighting, OSRAMSylvania
Visual recovery studies
National Highway Traffic Safety Administration
John Van Derlofske, Peping Dee, JenniferWatkinson, Jie Chen