- The Washington Times - Friday, March 1, 2002

Complaints about headlight glare have been around for decades.

When halogen lights began to replace incandescent lamps in the late 1970s, automakers were deluged with complaints about "those bright white lights." Now, halogens are basic standard equipment, but other advances in headlight design are starting to appear and not without controversy.

The latest development in headlight technology is the so-called high-intensity discharge lamp system or HID. Some automakers call them xenon lights, referring to the gas that surrounds the electric arc that produces the light. HID headlamps have a distinctive appearance. The color is much whiter than halogen lamps and, like daylight, appears to be light blue. That bright appearance is the basis for many complaints. But preliminary research shows that HIDs aren't the only source of headlight glare.

Responding to motorists' complaints, the National Highway Transportation Safety Administration recently solicited public comment about headlight glare. At about the same time, the AAA Foundation For Traffic Safety commissioned a study to investigate the sources of headlight glare and possible countermeasures for reducing its effects. The results of the investigation are in some ways surprising, and in other ways expected.

Most surprising is the finding that misaligned headlamps are the most likeliest source of headlight glare. Fifty percent of vehicles have one or more headlamps misaimed and the problem grows worse with age (5-year-old vehicles are almost twice as likely to have misaimed headlamps as 1-year-old vehicles). Vertical misaim is the principal concern, as just a 1-degree elevation of headlamp can result in a four-to-eight-fold increase in rearview mirror glare.

It's easy to believe that maintenance of headlight aim is something that most motorists would attend to, but there is little incentive to do so. Drivers are likely to correct their own misaimed headlamps only when they don't provide adequate visibility on the road ahead, and this situation usually doesn't create a glare problem. If misaimed headlamps are creating a glare problem, the driver is likely to think they are fine, because the increased glare production is associated with improved visibility.

Further, the study states that without an enforced limit to the amount of misaim, it is impossible to control the most likely source of headlight glare. While regulation of vehicle inspection is thought to be a state issue, federal involvement may be appropriate.

As expected, the study finds that glare increases as headlamp size shrinks. Automakers are reducing headlamp size while simultaneously increasing beam strength. (HIDs are two to three times brighter than standard halogen headlamps.) Projector HIDs, which are very small, are a particular concern in this regard.

The AAA Foundation for Traffic Safety suggests that NHTSA should consider banning projector HIDs and setting minimum headlamp sizes.

Another study finding should come as no surprise to those who drive a small car and have been irritated by mirror glare from a light truck. The study states that lowering headlamp height in light trucks representing 50 percent of all light-vehicles sales, lowering the headlamp height of these vehicles should be pursued.

The study further suggests countermeasures that the driver might use against glare. The most obvious, and perhaps less-used, is the day-night rearview mirror that requires the driver to flip the mirror from day to night mode. Drivers need to be encouraged to use the night setting and to aim the left outside mirror so it does not reflect directly into their eyes.

Better yet is an automatic glare-reduction mirror in both the rearview and left-side positions. The AAA Foundation recommends that NHTSA consider mandating such mirrors, while pursuing additional research into other self-dimming technologies and related human-factor issues.

Finally, research appears to show that, for most individuals, night-driving glasses are not an effective solution to glare problems. What is gained in the reduction of discomfort is loss in visibility. This conclusion applies to both full-eye glasses and half-glass analyzers that allow the driver to look through the analyzer only on demand.

There appears to be no clear-cut answer to the glare problem. More research is needed to better understand the relationship, if any, between discomfort and eye fixations, attention and fatigue.

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