Kelvin is mentioned often in this blog and other places dealing with light. But what does it say about a lamp? And then there’s wavelength. Those of you looking for both in the regulations won’t find anything though – so let’s search for some reliable information.
For friends of bluish light there’s nothing better than as many kelvins (K) as possible. The higher this color temperature unit the colder the light, which is due to the high proportion of blue. Today we don’t want to talk about whether blue makes sense or not. Today the question isn’t “how much blue is there supposed to be?” but “how much blue is there allowed to be?”.
Their rules 37, 48, 98 and 128 deal with light colors, among other things, including those of indicators and red lights. But you won’t find anything about kelvin in them.
The ECE regulations are just much more precise. They define colors and their limits as coordinates in the color space, in other words the visible light perceived by the eye. That’s useful for physicists but not for someone buying lamps. As a rule of thumb, the limit for blue is reached at around 6000 kelvins. If a lamp promises more it’s probably not legal. Other color nuances are also restricted by what is known as “ECE white”. In practice this particularly applies to yellow glow. The old full-on yellow lights from France are excluded – much to the dismay of their very small fan base.
Color plays a role not only for headlight lamps but also for yellow indicators and the red in braking and rear lights, the color of which is often specified as the wavelength of the light. By the way, with this number it’s the other way round compared to headlights – the lower values for the wavelength are more important, which means that the color is more saturated. This works really well with LEDs, also because they only provide a very narrow color spectrum. The ECE also defines red and yellow through coordinates and not through wavelengths or color temperatures. When you buy lamps from Osram for indicators and rear lights, they automatically come with the approved values.