Headlamp washers often are still referred to as headlamp wipers. But the systems with the little wipers disappeared along with glass headlamp lenses. Headlamps with polycarbonate lenses would only get scratched by the wiper blades. The latest form of the headlamp washer is a high pressure cleaning system.
It is a widespread fallacy that headlamp washers are only compulsory for xenon lights. This is wrong on several counts. The latest generation of xenon, the 25-Watt version, doesn’t actually need one at all. Meanwhile, halogen and LED headlamps do need one if their light sources emit more than 2000 lumens. Indeed, this is required for ECE approval. (Under the DOT regulations in North America headlamp washers are not mandatory at all.) These do not refer specifically to xenon, but as no approved halogen lamp exceeds this threshold value and as this also is the case with most LED systems, only xenon headlamps are, in fact, affected in practice. They emit around 3000 lumens.
„Hold on though,“ the insiders will be saying, „There are halogen lamps with an output of over 2000 lumens.“ That’s quite true: The H9 is one such lamp, emitting 2100 lumens. But this lamp is intended for high-beam light and the ECE regulations only apply to the low beams.
So why do headlamps need a washer system at all? Most people think it is so that dirt cannot dim the light. This is only partly true, and in fact, this wouldn’t be a particularly crucial concern with xenon lights, which have such a very high light output. The main reason for the requirement is that dirt can impair the optical features of the headlamp and cause glare. Incidentally, headlamps which are only slightly soiled cause a stronger glare, and of course the brighter the headlamp, the stronger the glare.
Headlamp washers originated in Scandinavia. From 1972 up to the early 1990s, they were compulsory in Sweden and today almost all cars in the country are supplied with them – even if they have halogen headlamps. The nozzles for the high-pressure washing system spray the water onto the headlamp lenses with pressures of up to 50 bar. Using an unsuitable antifreeze or insect remover in the summertime can wreak all kind of damage. The headlamp lenses are dulled prematurely: New headlamps are expensive – much more expensive than buying antifreeze and the like from a reputable brand.