Turn signal colour
Until the early 1960s, most front turn signals worldwide emitted white light and most rear turn signals emitted red. Amber front turn signals were voluntarily adopted by the auto industry in the USA for most vehicles beginning in the 1963 model year, though front turn signals were still permitted to emit white light until FMVSS 108 took effect for the 1968 model year, whereupon amber became the only permissible colour for front turn signals. Presently, almost all countries outside North America require that all front, side and rear turn signals produce amber light. In North America the rear signals may be amber or red. International proponents of amber rear signals say they are more easily discernible as turn signals. U.S. studies in the early 1990s demonstrated improvements in the speed and accuracy of following drivers' reaction to brake lamps when the turn signals were amber rather than red.[28][29][30][31][32] American regulators and other proponents of red rear turn signals have historically asserted there is no proven lifesaving benefit to amber signals, though a 2008 U.S. study suggests vehicles with amber rear signals rather than red ones are up to 28% less likely to be involved in certain kinds of collisions.[33]
There is some evidence that turn signals with colourless clear lenses and amber bulbs may be less conspicuous in bright sunlight than those with amber lenses and colourless bulbs.[34]
[edit] Colour durability
The amber bulbs commonly used in turn signals with colourless lenses are no longer made with cadmium glass, for cadmium is banned due to its toxicity by various regulations worldwide, including the European RoHS directive[35]. Amber glass made without cadmium is very costly, so most amber bulbs are now made with clear glass dipped in an amber coating. Some of these coatings are not as durable as the bulbs themselves; with prolonged heat-cool cycles, the coating may flake off the bulb glass, or its colour may fade. This causes the turn signal to emit white light rather than the required amber light. The international regulation on motor vehicle bulbs requires manufacturers to test bulbs for colour endurance[36]. However, no test protocol or colour durability requirement is specified. Discussion is ongoing[37] within the Groupe des Rapporteurs d'Éclairage, the UNECE working group on vehicular lighting regulation, to develop and implement a colour durability standard. Rather than using an amber bulb, some signal lamps contain an inner amber plastic enclosure between a colourless bulb and the colourless outer lens.