LEDs are more and more applied for routing information on electronic signs in road traffic. There are indications from the USA that some types of sunglasses almost totally block the yellow light of these LEDS, which made the signs illegible. For the Dutch Ministry of Transport an inventory was made of these special sunglasses and yellow LEDs and an estimation was made of the expected effects of this phenomena. Therefore (1) an inventory was made of the relevant standards for sunglasses, traffic lights, car windscreens and variable message signs, (2) the spectral transmission of two types of special and three types of normal sunglasses was measured, (3) the relative spectral radiant intensity of six yellow LEDs was measured, and (4) using the measured spectra light transmissions, colour coordinates and contrasts were calculated. It appears that the special sunglasses comply with the American standard but not with the European (draft) standard for sunglasses, because the European standard requires a minimum spectral transmission between 500 and 650 rim. Special sunglasses have a transmission between 4 and 10% for the light of yellow LEDS. Legibility distance of signs equipped with yellow LEDs decrease with 30 to 50% when special sunglasses are used. For normal sunglasses the legibility distances often increase. The colour coordinates of the most LEDS, seen through sunglasses, meet the requirements of the CEN for variable message signs. Only the Sharlight LED, in combination with special sunglasses falls outside the prescribed colour area. For the light of low-pressure sodium lamps the special sunglasses have transmissions between about I and 5%. When during the daytime, while wearing special sunglasses, a tunnel is entered lighted with low-pressure sodium lamps, the perceived light level suddenly can decrease to risky low values. It is recommended the manufacturers and importers attention should be drawn to the fact that special sunglasses do not comply with the European (draft) standard and that the use of these sunglasses in road traffic is hazardous. In that case, yellow LEDs can be applied for information carriers along the road without restrictions. However, there is a preference for white LEDs with a broad spectrum. (A)
Abstract