Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement

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


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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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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)


7/23 2008 Rensselaer Polytechnic Institute. All rights reserved.

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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



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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)



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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



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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



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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



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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



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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

Spectral and Temporal Factors Associated With Headlight Glare Implications for Measurement

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