Wikipedia 說的不見得都對，但至少是個參考。

http://en.wikipedia.org/wiki/Automotive_lighting#Rear_fog_lamps

In Europe and other countries adhering to ECE Regulation 48, vehicles must be equipped with one or two bright red "rear fog lamps" (or "fog taillamps"), which serve as high-intensity rear position lamps to be energised by the driver in conditions of poor visibility to enhance vehicle conspicuity from the rear. The allowable range of intensity for a rear fog lamp is 150 to 300 candelas,[15] which is within the range of a U.S. stop lamp.