In winter it is extra noticeable: bright headlights. Car headlights are the most eye-catching, but scooters and cyclists are just as likely to cause glare. Why are many headlights so unpleasant for other road users?
The subject is alive, as is also evident from a survey that the ANWB has just conducted among its followers and members. “We received more than 10,000 responses, much more than we expected,” says Harm Zeven of the ANWB. “We are still analyzing, but it was immediately noticed that young and old are complaining about glare. Some say that it is only a problem for the elderly, and that they should no longer drive at night. So that’s nonsense.”
Complaining about bright light has always existed, says Johan Alferdinck of the Dutch Foundation for Enlightenment Science. “When I started doing lighting research at TNO in the 1980s, the halogen headlight was on the rise. Before that there was the incandescent lamp, which was more yellow, and people thought the halogen lamp was too white and too bright. People keep getting used to it. Incidentally, the standards for the maximum light intensity towards oncoming traffic have changed over the years: in the beginning it was 375 candela (for two lamps together), in the halogen period 500 candela, and now it is 700.”
The color of the light also affects the experience. A few years ago, xenon lighting was popular for a while. “That is very white light. And although it was not necessarily brighter, it was experienced as irritating light,” says Alferdinck.
The headlights that are currently so blinding – a term that includes both discomfort and restriction of vision – are usually LED lamps. “Glare is experienced when somewhere in the visual field there is a light source that is substantially brighter than you are used to,” says Ingrid Heynderickx, professor of applied visual perception at TU Eindhoven.
It has to do with how your eyes scatter the light. “LED does not provide more light, but the same amount of light does come from a small light source, almost a point source,” says Heynderickx. “That light is strongly scattered in the eye, but apparently remains a narrow, high peak compared to the general light level in your eye. The higher such a peak is compared to the general light level, the more glare. That is why you are less bothered by the same LED lighting during the day than in the dark. In older people, scattering in the eye is stronger, due to crystal formation in the eye fluid. That is why they are more likely to suffer from glare.”
Less stray light
LED lighting has major advantages. It is very energy efficient and the light beam is easy to direct, resulting in less stray light and light pollution in the environment. For these reasons, street lighting is now also often LED. “But the disadvantage is that that well-directed light can suddenly be projected completely onto your eyes if a car or bicycle drives over a threshold or the lamp is incorrectly adjusted,” says Heynderickx.
Directing the light differently can help. “That is possible with reflectors in the lamp unit,” says Zeven. “Then the LED light first goes to the back and the reflector projects it forwards. This makes the light beam wider and less annoying to the eye.”
Yet automakers hardly apply this. “They are very concerned with streamlining and identity. You can make LEDs nice and narrow, or put them in a characteristic shape.” Or as the ANWB put it in a 2019 study of headlights: “What makes car designers happy is what annoys motorists.”
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