Originally Posted by stevenva
Someone above said to match the led color output to lens color, (like a red led behind a red lens). Not true. You want the brightest, whitest light behind that colored lens for optimum output.
Sorry, but you're wrong there. This is a rule that does not apply to regular bulbs, but is an important distinguishing characteristic for LEDs.
For a normal bulb, you simply want the brightest white bulb possible. This is because the bulb emits truly white light, and then the colored lens on the vehicle will filter all the light out and allow only the red or orange portion of the spectrum to pass through. You want the brightest bulb possible so that when you effectively cut out some of the other light, you still have a bright bulb. You also don't want a colored bulb, because all you are doing is making the bulb dimmer by filtering the red or orange portion twice - which is basically like putting two layers of tint on your windows.
LEDs function differently from regular bulbs in how they generate light. They are really only good at producing a certain color of light. It was actually rather challenging to create a "white" LED originally. You might notice that some LEDs do this by using three colors (much like a pixel on your LCD screen). The most common way is to use a fluorescent material that absorbs some lower wavelengths and re-emits it across the visible spectrum. So putting a colored filter in front of a white LED results in light which has been absorbed and re-emitted (with some loss) and then additionally filtered down to a single color.
There is a reason that every single LED bulb site posts a notice saying that the bulb color you buy must match the color of the lens on your vehicle. It's not a made-up lie - there is a very reasonable scientific explanation behind it.