It has long been understood that dirt has two effects: the scattering of light and the reductions of light in the more intense parts of a headlamp beam pattern. Although loss of light in intense areas is undesirable, the main concern with the effects of dirt on headlamps is often the increases of light that can occur in the less intense areas, since those increases can result in more glare to the other road users.
Water deposit provokes the same modifications of the headlamp beam pattern, but one can estimate that the aerodynamic forces eliminate the droplets quickly. This recommended practice thus concerns only the durable accumulation of solid soiling that the headlamp cleaners eliminate or reduce.
In comparison to the preceding version, this standard is modified as follows:
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