DRL Induced Glare

An Analytical Study of the Effectsof Peak Luminous Intensity

NHTSA Proposed RulemakingAugust 7, 1998

Federal Motor Vehicle Safety Standard 108:

Lamps, Reflective Devices and Assoc. Equip.

Proposed Rule Change:

Reduction in the maximum permitted

luminous intensity for vehicle daytime

running lights [DRLs]

Rational for Proposed Rulemaking

400+ complaints re: excessive glare

from U.S. public on file

(N.B. Virtually no complaints in Canada)

“This action is intended to provide the

public with all the conspicuity benefits of

DRL’s while reducing glare”

U.S. DRL Intensity Specification

Current Maximum: 7000 cd

compatible with Canadian specification

compatible with high-beam headlamps

operated at half voltage

34-inch maximum mounting height

(else 3000 cd – rearview mirror glare)

Proposed Maximum: 3000 cd (Phase I)

1500 cd (Phase II)

demonstrated “conspicuity” benefits under

high ambient daytime illumination

(based on “search conspicuity” paradigms)

minimal discomfort glare

(especially re: rearview mirrors)

Modeling the Magnitude of Glare Effects

Disability GlareAdrian & Bhanji (1991) equation

Relative elevation of contrast threshold

Discomfort GlaredeBoer Subjective Rating Scale

Schmidt-Claussen & Bindels (1974) model

Analytic Conditions

(4) DRL Intensities

1500, 3000, 5000, 7000 cd

(Proposed – Current NHTSA Maximum)

(5) Observation Distances

20, 40, 60, 80, 100 m

(6) Driver Light Adaptation States

1, 50, 100, 500, 1000, 5000

(Dark-to-Brightest Summer Day)

Driver Luminance Adaptation States

Adaptation Ambient

Time of Day State Illumination

(cd/m2) (lux)

road at night 5 100

twilight / dawn 250 5000

clear winter day 500-150010,000-30,000

brilliant summer day 5000 85,000+

Luminance (cd/m2) = illumination (lux) * reflectance / p

assumption: average scene reflectance = 0.15

(asphalt road = 0.10, grass = 0.20)

Adrian & Bhanji (1991)Disability Glare Model

Lequivalent = k

2

glare

k

glare is the illumination of the glare source at the eye of the observer (lux)

= 9.05Age (in years)

66.4( )

4

1 +( )is the angle between the glare source and the observer's line-of-sight (degrees)

where:

( Equation 1 )

Influence of Veiling Luminance(Reduction of Retinal Contrast/Visibility)

Nominal Contrast = Ltarget

– Lbackground

/ Lbackground

Ltarget

+equivalent

Lbackground

L

+equivalent

L( ) +equivalent

Lbackground

L( )-Contrastglare

=

+equivalent

Lbackground

L

backgroundLL

target-

=

Effects of Glare upon Contrast Sensitivity(Due to Veiling Luminance)

+equivalent

L

Threshold elevation =

backgroundLL

target -

backgroundL

backgroundL

backgroundLL

target-

(

(

)

)

Threshold elevation = Retinal Contrast without Glare Retinal Contrast with Glare

1% Contrast Elevation Factor

backgroundL ( 0.01 ( ) ) / (

backgroundL

equivalentL+ )

0.01

Blackwell (1946) showed that small and mid-size objects in theroadway environment can be detected at a contrast of 1%across a broad range of photopic luminance levels.

The effect of veiling retinal luminance upon this nominaldetection threshold can be estimated as follows:

Glare Illumination:Viewing Distance & DRL Intensity

Disability Glare Drops Rapidlywith Increasing Luminance Adaptation

10001001010

2

4

6

8

10

12

7000

5000

3000

1000

75-year-olds20m (8.93 degrees)

Luminance Adaptation (cd/m2)

Con

tras

t T

hre

shol

d E

leva

tion

DRL Intensity

Conclusion:

DRLs can cause some “disability” at nighttimebut not betweendusk and dawn.

But…What about“discomfort” glare?

Discomfort Glare

deBoer Subjective Rating Scale

1 Unbearable23 Disturbing45 Just Acceptable67 Satisfactory89 Just Noticable

Schmidt-Claussen & Bindles (1974)Disability Glare Model

deBoer Discomfort

Glare Rating= 5.0 - 2 log

glare

0.003 )(1 + backgroundL

0.04

0.46

backgroundL

glare is the illumination of the glare soure at the eye of the observer (lux)

is the angle between the glare source and the observer's line-of-sight (minarc)

is the background adaptation state of the observer (cd/m2)

where:

deBoer Discomfort GlareDRL=1500 cd; Changing Adaptation Level

10080604020001

2

3

4

5

6

7

8 1500 cd

Distance (m)

Dis

com

fort

Gla

re R

atin

g

50 cd/m2100 cd/m2

500 cd/m21000 cd/m2

5000 cd/m2

Comfort

Discomfort

Adaptation LevelDay/Clear Sky

Dusk/Dawn

deBoer Discomfort GlareDRL=3000 cd; Changing Adaptation Level

10080604020001

2

3

4

5

6

7

8 3000 cd

Distance (m)

Dis

com

fort

Gla

re R

atin

g

50 cd/m2100 cd/m2

500 cd/m21000 cd/m2

5000 cd/m2

Comfort

Discomfort

deBoer Discomfort GlareDRL=5000 cd; Changing Adaptation Level

10080604020001

2

3

4

5

6

7

8 5000 cd

Distance (m)

Dis

com

fort

Gla

re R

atin

g

50 cd/m2100 cd/m2

500 cd/m21000 cd/m2

5000 cd/m2

Comfort

Discomfort

deBoer Discomfort GlareDRL=7000 cd; Changing Adaptation Level

10080604020001

2

3

4

5

6

7

8 7000 cd

Distance (m)

Dis

com

fort

Gla

re R

atin

g

50 cd/m2100 cd/m2

500 cd/m21000 cd/m2

5000 cd/m2

Comfort

Discomfort

Saturn Special CaseAlternator Over voltage => 10,000 cd

10080604020001

2

3

4

5

6

7

8 10000 cd

Distance (m)

Dis

com

fort

Gla

re R

atin

g

50 cd/m2100 cd/m2

500 cd/m21000 cd/m2

5000 cd/m2

Comfort

Discomfort

DRL Discomfort Borderlines

1008060402000

Distance (m)

Dis

com

fort

Gla

re R

atin

g

50 cd/m2100 cd/m2

500 cd/m21000 cd/m2

5000 cd/m2

1500 cd

3000 cd5000 cd7000 cd

10000 cd

Adaptation State

DRL Intensity

Discomfort

Comfort

European Glare Sensitivity?

1000010001001

2

3

4

5

6

7

8

9

UMTRI (1999)Schmidt-Claussen & Bindels (1974)

DRL Intensity (cd)

deB

oer

Dis

com

fort

Rat

ing

DRL Intensity > 2000 cdSmall Gains in Visibility

Large Increases in Discomfort

1000010001001010.0

0.2

0.4

0.6

0.8

1.0

DRL Intensity (cd)

Vis

ibil

ity

Ben

efit