SLIDE 1:
NHTSA Workshop: Balancing Visibility and Glare: WHAT IS GLARE?


John Van Derlofske, PhD, 
John Bullough, PhD

Transportation Lighting Group
Lighting Research Center
Rensselaer Polytechnic Institute


SLIDE 2:
What is "glare"?

* "DICTIONARY" DEFINITION:
A harsh uncomfortably bright light <the glare of a neon sign> <the glare of publicity>; especially: painfully bright sunlight

* GLARE OCCURS IN TWO WAYS:
  - too much light
  - luminance range is too large

* EFFECTS OF GLARE:
  - photobiological damage: not considered here
  - disability glare: reduction in visibility
  - discomfort glare: annoying or painful sensation
  - recovery (readaptation): visual performance returning to its initial state


SLIDE 3:
DISABILITY GLARE

* reduction in visibility can be attributed to light scatter in the eye

* the magnitude of disability glare can be estimated by the veiling luminance L(pi)


SLIDE 4:
DISABILITY GLARE
This effect is exhibited in luminance contract C: [photos]


SLIDE 5:
DISABILITY GLARE
* A subjective feeling of annoyance caused by high luminance in the field of view:

De Boer Scale: (De Boer, 1967)

RATING/ Qualifer
1	unbearable
2
3	disturbing
4
5	just acceptable
6
7	satisfactory
8
9	just noticable

(Schmidt-Clausen & Bindels, 1974)


sLIDE 6:
RECOVERY (READAPTATION)
* readaptation to lower light levels after glare exposure takes time

* visual performance is reduced during this recovery period


SLIDE 7:
WHAT DO WE KNOW?
GLARE & VISUAL PERFORMANCE
* Parameters that affect visual performance (e.g. Mace et al, 2001):

Glare parameters:
 - illuminance at the eye
  (Schmidt-Clausen & Bindels, 1974; Flannagan et al, 1996; bullough et al, 2003 and glare formulae)

 - angle of the glare source
 (fry, 1954; fu, 2001 and glare formulae)

 - luminance/size
(Flannagan, 1999; Bulough et al, 2003)

 - spectral power disturibution
  (Flannagan, 1999; Bulough et al, 2002, 2003)

 - duration of exposure
  (Fry, 1973)


sLIDE 8:
WHAT DO WE KNOW?
GLARE & VISUAL PERFORMANCE
* Parameters that affect visual performance (e.g. Mace et al, 2001):

* Environmental Parameters:
  - ambient conditions
  (Andre & Owens, 1999; Akashi et al, 20003; Carlson & Urbanik, 2004)

  - complexity/difficulty of location
  (Theeuwes & Alferdinck, 1996; Bullough et al, 2003)

* Observer parameters
  - age, visual health
  (Campbell et al, 1998; Higgins & White, 1999; Schmitz et al, 2000; Peli, 2002; McGwin et al, 2003; schieber)


SLIDE 9:
ILLUMINANCE AT THE EYE

Increased glare illuminiance results in increased veiling luminance, which decreases luminance contrast


SLIDE 10:
LUMINANCE / SIZE

size of glare source (0.3 degrees or 0.6 degrees) had no impact on detection of target (Flannagan, 1999)


SLIDE 11:
SPECTRAL POWER DISTRIBUTION
Glare SPD has no impact on target detection (Bullough et al, 2003)


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SLIDE 29:
EXPERIENCE / EXPECTATIONS	
Ratings in North American reported to be 1 to 2 De Boer ratings higher than that in Europe (Sivak et al, 1989)


SLIDE 30:
AGE/VISUAL HEALTH
Age may have a small impact on feelings of discomfort from glare (Olson & Sivac, 1984; Dee, 2003)

<<Research shows contradictions: see also Tsongos & Schwab, 1970; Flannagan et al, 1993; Theeuwes & Alferdinck, 1996; Sivak et al, 1999; Dee, 2003>>



SLIDE 31:
ADDRESSING THESE ISSUES
Using new source technologies, system technologies, and optical design strategies

- beam photometry
	* new distributions
	* active distributions
(advanced front lighting systems, AFS)



SLIDE 32:
ADDRESSING THESE ISSUES
Using new source technologies, system technologies, and optical design strategies

- headlamp luminance/size
 >>multi-source systems can distribute luminance<< 


SLIDE 33:
ADDRESSING THESE ISSUES
Using new source technologies, system technologies, and optical design strategies

- beam spectrum:
 	new spectral distributions
	increase visibility
	decrease glare

>> decreased short wavelength content to decrease discomfort<<

>> increased short wavelength content to increase visual performance <<

SLIDE 34:
CONCLUSIONS	
Much is known about glare and visual performance and discomfort

However, metrics are lacking

 - relatively little is known about how glare affects driving behavior (Aktan & Schnell - 2003) and safety

 - NHTSA and the LRC are performing a 100-car naturalistic study to start to answer these questions