NHTSA comments about about HID's (long)
10-04-2001, 05:54 AM
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NHTSA comments about about HID's (long)
The next time somebody gets pissy bout your headlights, lay this on 'em:
2.2 - Glare from High Intensity Discharge Headlamps
In the case of HIDs, we have received numerous complaints stating that these newer lamps produce excessive glare. Even though they are required to comply with all federal lighting requirements and we have no reason to believe that they do not comply, HIDs are still being singled out as being troublesome glare producers for other drivers. The reason expressed by drivers is that the HID headlamps are brighter. This may be due to the spectral content of the produced light, the generally wider and more robust beam pattern, and/or their conspicuous color relative to other headlamps, or misaim.
In an effort to create a headlamp which provides better illumination, longer life, and a unique styling appearance, vehicle lighting manufacturers developed HIDs. They have been typically offered on higher end vehicles and can cost as much a $400 to $800 for the option. HIDs are unlike conventional halogen headlamps in that they operate more like street lamps. Instead of heating a tungsten filament, an electrical arc is created between two electrodes. This excites a gas inside the headlamp (usually xenon) which in turn vaporizes metallic salts. These vaporized metallic salts sustain the arc and emit the light used for the headlamp's beam. These lamps provide more light than that produced by halogen lamps and only use two-thirds the power. As a result, they are more efficient, and because there is no filament to burn out, these bulbs are claimed to last for as much as 100,000 miles of driving time.
Although the agency has seen advertising and received many complaints claiming that the light produced by HIDs is twice or three times as bright as that which is produced by halogen lamps, laboratory measurement, made by various parties, do not support these claims. HID light sources (bulbs) typically have about two to three times the available light flux (volume) of halogen light sources, but because of such an abundance of light, the HID optical design does not necessarily need to be as efficient at collecting and distributing light as a halogen system. The HID beam pattern is certainly more robust, providing more even and wider illumination and the potential for better visibility and comfort. This performance results in more light on the road surface and more of the roadway being illuminated. However, this additional light is not supposed to be projected upward from the lamp toward other drivers' eyes. During inclement weather, when the road surface is wet, the additional volume of light can result in higher levels of light reflected off the road surface into other drivers' eyes. However, those who have complained about HID glare have not specifically reported inclement weather as the only time when there is a problem with HID glare.
Another factor that may be involved is the phenomenon that may have occurred with the introduction of halogen lamps in the early 1980's. Drivers are attracted to headlamps that are different colors than would normally be seen. As such, the drivers may look directly at oncoming headlamps during driving to see the unfamiliar item. This is something that they do not normally do. Initial halogen headlamp introduction elicited some glare complaints, even though the first halogens used were actually very similar in performance to the standard non-halogens headlamps. The only marked difference was the color of the halogen headlamps. If this is the case now, one would expect glare complaints about HIDs to stop when drivers become familiar with the HID color. NHTSA is aware of no studies or evidence to suggest that this theory is correct.
Another factor that may lead to the perception that HIDs are significantly brighter than halogen lamps is that human eyes may be more sensitive to bluish-white light of HIDs than to yellowish-white light of halogens. When observing some HIDs, it may seem that they are not emitting white light, as required by Standard No. 108. However, when observing the beam pattern projected on a white screen, HID headlamps that comply with our lighting standard will appear to be white with color separations occurring only at the extreme edges of the pattern. Non-halogen, halogen, and HID light sources appear to be different colors to observers. Non-halogen lamps appear to be yellow when compared to halogen lamps, and halogen lamps appear to be yellow when compared to HIDs.
In a recent study by the University of Michigan Transportation Research Institute (Flannagan, M. J.; 1999, ASubjective and Objective Aspects of Headlamp Glare: Effects of Size and Spectral Power Distribution," Report No. UMTRI-99-36, available in Docket Number: NHTSA-2001-8885-3) the differences reported between halogen versus HID lamps caused a small but statistically significant difference in discomfort glare noted by observers. However, it had no effect on disability glare. It is not known yet whether it is the difference in spectral power density of these headlamps, but this difference in the human eye's glare response to these different lamp designs is shown in that study.
HIDs are not just more white (having less yellow content and more blue content in the emitted spectrum), but the light is generated in a different manner. HIDs achieve light by having vaporized metallic salts participate in the electrical current flow through an arc in the bulb capsule. This is contrasted to a heated metal filament which gives a relatively even level of light at all colors in the spectrum, and thus achieves smoother white light. The HIDs blend of metallic salts is designed such that the different salts, emitting different colors of light with different energy levels, will complement each other when fully heated and electricity is passed through them, because each salt contributes various frequencies of light and at different levels of energy. The result is white light, but with a few relatively high energy spikes of light at very narrow bandwidths. These spikes are obvious in a mapping of the spectral power density of the light emitted. (See Docket Number: NHTSA-2001-8885-4, USA Today, June 7, 2001, "Bright Lights, Big Controversy" by James R. Healey, page 1, the side bar Aharsh blue light contributes to glare"). This comparison shows that the light spectrum of HIDs is not as smooth as the light from a heated filament in a halogen lamp. It is possible that our eyes are not necessarily reacting to the whiter light, but to the high energy spikes that rise above a background energy achieving the white light. If this is a cause for the UMTRI findings, it may be that a redesign of the HID system is necessary. However, this is just a theory, with no supporting data. NHTSA is initiating research to study all potential factors that may be causing HIDs to be an annoying lighting source.
2.2 - Glare from High Intensity Discharge Headlamps
In the case of HIDs, we have received numerous complaints stating that these newer lamps produce excessive glare. Even though they are required to comply with all federal lighting requirements and we have no reason to believe that they do not comply, HIDs are still being singled out as being troublesome glare producers for other drivers. The reason expressed by drivers is that the HID headlamps are brighter. This may be due to the spectral content of the produced light, the generally wider and more robust beam pattern, and/or their conspicuous color relative to other headlamps, or misaim.
In an effort to create a headlamp which provides better illumination, longer life, and a unique styling appearance, vehicle lighting manufacturers developed HIDs. They have been typically offered on higher end vehicles and can cost as much a $400 to $800 for the option. HIDs are unlike conventional halogen headlamps in that they operate more like street lamps. Instead of heating a tungsten filament, an electrical arc is created between two electrodes. This excites a gas inside the headlamp (usually xenon) which in turn vaporizes metallic salts. These vaporized metallic salts sustain the arc and emit the light used for the headlamp's beam. These lamps provide more light than that produced by halogen lamps and only use two-thirds the power. As a result, they are more efficient, and because there is no filament to burn out, these bulbs are claimed to last for as much as 100,000 miles of driving time.
Although the agency has seen advertising and received many complaints claiming that the light produced by HIDs is twice or three times as bright as that which is produced by halogen lamps, laboratory measurement, made by various parties, do not support these claims. HID light sources (bulbs) typically have about two to three times the available light flux (volume) of halogen light sources, but because of such an abundance of light, the HID optical design does not necessarily need to be as efficient at collecting and distributing light as a halogen system. The HID beam pattern is certainly more robust, providing more even and wider illumination and the potential for better visibility and comfort. This performance results in more light on the road surface and more of the roadway being illuminated. However, this additional light is not supposed to be projected upward from the lamp toward other drivers' eyes. During inclement weather, when the road surface is wet, the additional volume of light can result in higher levels of light reflected off the road surface into other drivers' eyes. However, those who have complained about HID glare have not specifically reported inclement weather as the only time when there is a problem with HID glare.
Another factor that may be involved is the phenomenon that may have occurred with the introduction of halogen lamps in the early 1980's. Drivers are attracted to headlamps that are different colors than would normally be seen. As such, the drivers may look directly at oncoming headlamps during driving to see the unfamiliar item. This is something that they do not normally do. Initial halogen headlamp introduction elicited some glare complaints, even though the first halogens used were actually very similar in performance to the standard non-halogens headlamps. The only marked difference was the color of the halogen headlamps. If this is the case now, one would expect glare complaints about HIDs to stop when drivers become familiar with the HID color. NHTSA is aware of no studies or evidence to suggest that this theory is correct.
Another factor that may lead to the perception that HIDs are significantly brighter than halogen lamps is that human eyes may be more sensitive to bluish-white light of HIDs than to yellowish-white light of halogens. When observing some HIDs, it may seem that they are not emitting white light, as required by Standard No. 108. However, when observing the beam pattern projected on a white screen, HID headlamps that comply with our lighting standard will appear to be white with color separations occurring only at the extreme edges of the pattern. Non-halogen, halogen, and HID light sources appear to be different colors to observers. Non-halogen lamps appear to be yellow when compared to halogen lamps, and halogen lamps appear to be yellow when compared to HIDs.
In a recent study by the University of Michigan Transportation Research Institute (Flannagan, M. J.; 1999, ASubjective and Objective Aspects of Headlamp Glare: Effects of Size and Spectral Power Distribution," Report No. UMTRI-99-36, available in Docket Number: NHTSA-2001-8885-3) the differences reported between halogen versus HID lamps caused a small but statistically significant difference in discomfort glare noted by observers. However, it had no effect on disability glare. It is not known yet whether it is the difference in spectral power density of these headlamps, but this difference in the human eye's glare response to these different lamp designs is shown in that study.
HIDs are not just more white (having less yellow content and more blue content in the emitted spectrum), but the light is generated in a different manner. HIDs achieve light by having vaporized metallic salts participate in the electrical current flow through an arc in the bulb capsule. This is contrasted to a heated metal filament which gives a relatively even level of light at all colors in the spectrum, and thus achieves smoother white light. The HIDs blend of metallic salts is designed such that the different salts, emitting different colors of light with different energy levels, will complement each other when fully heated and electricity is passed through them, because each salt contributes various frequencies of light and at different levels of energy. The result is white light, but with a few relatively high energy spikes of light at very narrow bandwidths. These spikes are obvious in a mapping of the spectral power density of the light emitted. (See Docket Number: NHTSA-2001-8885-4, USA Today, June 7, 2001, "Bright Lights, Big Controversy" by James R. Healey, page 1, the side bar Aharsh blue light contributes to glare"). This comparison shows that the light spectrum of HIDs is not as smooth as the light from a heated filament in a halogen lamp. It is possible that our eyes are not necessarily reacting to the whiter light, but to the high energy spikes that rise above a background energy achieving the white light. If this is a cause for the UMTRI findings, it may be that a redesign of the HID system is necessary. However, this is just a theory, with no supporting data. NHTSA is initiating research to study all potential factors that may be causing HIDs to be an annoying lighting source.
10-04-2001, 06:01 AM
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I don't see what the big deal is. I've never noticed any excess glare, nor has anyone even ever mentioned excess glare to me from the lights.
I honestly think it's a case of the have nots trying to take away from the haves.
I honestly think it's a case of the have nots trying to take away from the haves.
10-04-2001, 07:17 AM
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Have any of you had a s2k drive towards you at night? I have twice and understand the complaints. Our lights jump around for some reason and give the impression of flashing our brights. I rarely drive my car at night now and usually hide behind an suv (which is easy here) when I do.
10-04-2001, 07:41 AM
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The irritation is real but, I think, caused more by our stiff suspensions than the lights. Another contributing factor is:
Since they mostly come on higher end cars, this increases the "ass factor" in them minds of many.
We also live in a particularly unique time in our history, I think. More and more, it seems that people believe that anything irritating should be outlawed. We've seen it here often enough in comments. Oddly, though, these people are some of the most irritating of all.
Originally posted by lvs2k
They have been typically offered on higher end vehicles and can cost as much a $400 to $800 for the option.
They have been typically offered on higher end vehicles and can cost as much a $400 to $800 for the option.
We also live in a particularly unique time in our history, I think. More and more, it seems that people believe that anything irritating should be outlawed. We've seen it here often enough in comments. Oddly, though, these people are some of the most irritating of all.
