The Flying Shingle
Focus on the Future
Bright white headlights: are they safe?
by Michael Mehta
Monday, January 2, 2012

There are two kinds of light – the glow that illumines, and the glare that obscures.” ~ James Thurber (American humourist, 1894-1961)
Driving at night on dark, two-lane, undivided, winding roads has become even more challenging in recent years. The introduction of super bright high-intensity discharge (HID) headlights in the mid-1990s has created an interesting transfer of risk and benefit between different users of the road.
Driving at night pushes our visual skills to the limit, and increased glare combined with reduced illumination impairs vision. The intense white (and sometimes bluish) light emitted by HID headlights is quite different from the yellowish, lower intensity light from older gas-filled filament-based incandescent headlights.
HID headlights allow owners to see farther down the road and to spot pedestrians and animals from a distance, but at the same time they can create visual chaos and temporary impairment to on-coming drivers, pedestrians and cyclists.
HID headlights are two to three times brighter than most incandescent headlights, and although considerably more expensive, they can cover more of the road (especially the sides), are durable, last longer, and use less power.
It’s interesting to note that HID systems are less effective when compared to the yellowish light from incandescent systems in fog, rain and snow. This is one of the reasons why fog lights are yellow.
Unfortunately, the benefits to the user can generate risks to other users of the road, and HID headlights can dazzle others making it more difficult for them to spot pedestrians, curves, and road hazards.
An article by Martin Mainster and colleagues (2003) entitled “Why HID headlights bother older drivers” in the British Journal of Ophthalmology noted that exposure to intense HID light is problematic for many older drivers since it reduces the ability of the eyes to detect contrasts through light scattering, while increasing exposure to uncomfortable glare and photostress that may involve startle responses and afterimages.
In general, older drivers are visually disadvantaged and sensitivity to headlight glare increases with age. An online brochure by the American Automobile Association (2008) on “How to avoid headlight glare” pointed out that a 55-year-old takes eight times longer to recover from glare than a 16-year-old, and that as our population ages complaints about glare will likely increase.
Evidence shows that HID lights have a stronger negative response in individuals with cataracts, those who wear glasses and/or who have received laser corrective surgery, and in those with lighter-coloured eyes. There are even anecdotal cases where HID light can generate pain to the point where people have given up driving at night, and a growing body of research shows that migraine headaches can be triggered by intense visual stimuli. Since 11 per cent of us suffer from migraines according to reports by the World Health Organisation, this is not a trivial issue.
Larger vehicles including SUVs and pick-up trucks with HID headlights generate the most concern since their headlights ride higher, and because many drivers of such vehicles continue to use fog lights simultaneously at night when not required. Although the correct aiming of headlights is critical to reduce the discomfort to oncoming drivers, even a variance of one degree too high can cause impairment, and studies show that more than half of vehicles on the road have at least one incorrectly aimed headlight.
A larger problem in some respects involves the growing popularity of conversion kits to turn an incandescent system into a HID one. Many kits include HID bulbs, ballast, wiring adapters, and relays, but these kits often do not include essential items like proper housings for the system. Please do not put HID bulbs in your stock halogen housings since these lower-cost conversions may create significant risks to other users of the road by producing excessive glare and light intensities that exceed the allowable candlepower by 800 per cent or more, and paradoxically provide only sub-par illumination to the user due to scattering effects.
So what can be done to reduce this problem?
If your vehicle is equipped with HID headlights, it is essential to ensure that they are aimed and configured correctly with the proper housings and reflectors. Do not convert incandescent systems into HID, and refrain when possible from using fog lights. Pick-up truck and SUV drivers should avoid following others too closely, and should think twice about the impacts on others when making decisions about “jacking up” their vehicles. Additionally, police should do more roadside surveillance.
To reduce the effects from on-coming vehicles, keep windshields clean, have chips and cracks repaired, avert eyes when possible, and learn how to use the night setting on the rearview mirror to reduce glare from behind. You may wish to also consider coating eyeglasses with an anti-reflective material. Lastly, as a courtesy to pedestrians, cyclists and other drivers, please lower your high-beam lights.

Dr. Michael Mehta is a sociologist who focuses on environmental and health risk issues.

Opinions expressed in this column will usually be those of the author and do not necessarily reflect those of The Shingle.

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