Although there are definitely car owners who prefer their headlamps to emit a yellowish light, they are extremely small in number and probably Francophile in attitude to culture or automobiles. The vast majority of people prefer a bluish light – or don’t care either way. But whatever your choice, you want it to be the same for both headlamps. Design fans are not happy when one headlamp reflects their chosen color tone, but the other is clearly different.
How can this happen in the first place? There are three main reasons for differences in light color between headlamps. The first is that the owner has combined a warm, yellowish-colored lamp with one that has a slightly bluish tint. Secondly, the lamps have been produced by different manufacturers. And thirdly, the bulbs are different in terms of age (i.e. length of service life). In each of these cases the solution is to always replace bulbs in pairs. Both bulbs must obviously be of the same type and from the same manufacturer. The fact that you can buy two headlight bulbs in one box is a real advantage here, and this is why Osram offers most of its automotive lamps in twin packs.
There’s a fourth reason for color differences, one that’s rare, but can’t be dealt with by replacing the bulb(s) – when one headlight has a higher operating voltage than the other. If this is the case, it’s a job for the repair shop.
It stands to reason that bluish glass bulbs emit a different light than ones that have no coloring. That there are variations between products from manufacturers is similarly easy to understand. But what role does the age of a lamp play? Color changes during the lifetime of a bulb are particularly noticeable with xenon lamps. Instead of the popular blush tint, xenon bulbs that are nearing the end of their service lives emit more of a violet or pink tone. But halogen lamps change with age as well, emitting a somewhat warmer light as they get older. Shortly before they burn out, halogen bulbs act as they’ve been given a new lease of life; they get brighter and emit light with a higher color temperature, becoming more bluish. Although this situation doesn’t last for very long, anyone changing just a single defective bulb during this period may end up with a more yellowish-looking beam.
Not only headlamps are affected
It’s not only headlight bulbs that are impacted by color differences due to age, type and manufacturer. Position or parking lights can be affected in a similar way. In the case of yellow signal lamps too, it’s clearly obvious when an owner has replaced a standard WY21W with an Osram Diadem. Here as well, and even if it’s only for aesthetic reasons, replacing lamps in pairs is a sensible idea.