The amber bulbs commonly used in turn signals with colourless lenses are no longer made with cadmium glass, since various regulations worldwide, including the European RoHS directive, banned cadmium because of its toxicity.Amber glass made without cadmium is relatively 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 bulb envelopes; 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. However, no test protocol or colour durability requirement is specified. Discussion is ongoing 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.
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