Main Light Sources for Headlights

Xenon - HID
· “Projector-style HID headlamps may be contributing to discomfort glare because their surface area is smaller than standard headlamps and so their luminance is much higher.”
http://www.aaafoundation.org/pdf/HeadlightGlare.pdf

· “HID headlamps typically have two to three times the light flux (volume) of halogen lights, but because the HID filament is smaller, they allow the light to be controlled more precisely.”
http://www.aaafoundation.org/pdf/HeadlightGlare.pdf

· “Properly aimed, and when not flashing, these HID lamps may not appear significantly brighter than halogen sources if their size is relatively the same. However, if misaimed, and when flashing, these lamps will appear brighter and will produce significantly more glare than a normal halogen lamp.”
http://www.aaafoundation.org/pdf/HeadlightGlare.pdf

· HID headlamps are more efficient than halogen headlamps and you can produce more light with a smaller headlamp; however, if you have too much then the contrast between the roadway directly in front of you and the area in your peripheral vision will be increased and potential for glare will increase
http://www.danielsternlighting.com/tech/bulbs/Hid/disadvantages/disadvantages.html

· Estimated to last the life of the vehicle (10 years, 160,394.4 km (100,000 mi)) under normal operating conditions – much longer than halogen lamp life
http://www.tfhrc.gov/safety/hsis/pubs/04146/introduction.htm

· Better performance and efficiency - “The luminous efficacy, which is the ratio of luminous output to electrical power consumption, is much greater in discharge lamps compared to halogen designs. Various lighting manufacturers claim that discharge lamps have at least twice the lumen output as halogen lamps with comparable wattage.”
http://www.tfhrc.gov/safety/hsis/pubs/04146/introduction.htm


Halogen
· Human eye’s color perception and differentiation is better under halogen light than under HID automotive headlamps
http://www.danielsternlighting.com/tech/bulbs/blue/bad/bad.html

· “light output of just over 1,000 lumens (lm) while operating at 12.8 volts (V)”; “average luminance of halogen bulbs can be around 1,400 candela per square meter (cd/m²) (408 footlamberts (fL)”
http://www.tfhrc.gov/safety/hsis/pubs/04146/introduction.htm

· disadvantage of halogen lamps is that “roughly 80 percent of the output is lost as heat in the infrared spectrum. In addition, the filaments in halogen systems can be damaged from road vibrations and other effects associated with long-term use. As a result, halogen headlamps may not last as long as other components in the vehicle.”
http://www.tfhrc.gov/safety/hsis/pubs/04146/introduction.htm

Visibility and Color Temperature of HID and Halogen Lamps

· Color correction to halogen and HID headlamps would reduce the amount of yellow light emitted which would promote night vision and visual acuity in darkness by improving our the ability to see contrast
· In addition this would lessen eyestrain and reduce the visual discomfort caused by headlights of oncoming vehicles at night and the amount of light can be increased without increasing eyestrain (also the addition of Neophane glass (neodymium oxide glass) would accentuate red and green hues so that an item like a red stop sign would stand out against a green background of trees-however this may make it more difficult to see other objects such as yellow warning signs) (Karpen Studies 1996, 1998, 1999, 2001 – Source: Countermeasures for Reducing the Effects of Headlight Glare)
http://www.aaafoundation.org/pdf/HeadlightGlare.pdf
http://www.aaafoundation.org/home/

· However, the above information also contradicts other information that states that although bluer HID light sources will aid the visibility of the driver, since these lamps emit more light than the halogen and the blue-white light can be somewhat blinding on oncoming drivers or for the drivers in front of you (i.e. glare of headlights in their mirrors) this is particularly harder on drivers as they age
http://www.aaafoundation.org/pdf/HeadlightGlareBrochure.pdf

· Other studies also indicate that while cooler, bluer white light improves visibility it also increases discomfort due to greater constriction of the pupil after brief exposures to light (Studies: Fugate and Fry 1956; Flannagan, Sivak and Traube 1994)
http://www.aaafoundation.org/pdf/HeadlightGlareBrochure.pdf

· Individuals may have different sensitivities to light within different parts of the color spectrum – some may be more sensitive to the bluer (cooler) white lights at the ultraviolet end of the spectrum than others and some may be more sensitive to glare than others
http://www.danielsternlighting.com/tech/bulbs/blue/bad/bad.html

· AAA Foundation for Traffic Safety doesn’t recommend color-corrected headlamps at this time due to lack of research but recommends further investigation. They also recommend further research regarding “the effect of neodymium (or other scotopically rich) headlamps on visibility and glare in a night highway environment. One thing is certain: If proven effective, neodymium headlamps should be cost-effective, because very little investment would be required to install the devices.”
http://www.aaafoundation.org/pdf/HeadlightGlare.pdf