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Changing the color of an LED bulb

  1. Jul 17, 2013 #1
    I recently changed my bulbs in my car's HVAC dash to LEDs. I wanted a blue color and it looks really good and exactly what I wanted. The only problem is that there are three buttons that are lit separately from the new LEDs by green bulbs, which I want to be blue as well, but I cannot simply change those bulbs (they are hard-wired in, not a plug-in-play bulb socket). Since I cannot change the bulb, my idea was to add a translucent color paper to the little "window" that displays the color on the button, but I don't know what color(s) to use. Basically, in other words, what color paper can I use to make green light turn to blue?

    To make matters more complicated, the temperature select button has a blue, white and red selector. They are all "supplied" with light from the new blue LED. Obviously the blue works, but the rest is all blue, which means I have one long blue strip, rather than three segmented colors. I would like to do the same thing with the color paper to get to white and red. I'm thinking for the white, I can add green and red paper together to make the white (the three primary colors together)? What about the red?

    Can any of this be done, or is there another way of going about it?

    Here is a picture of my dash for reference. I can add more pics if necessary. You can see the two green color buttons and the one yellowish-green button as well as the temp. select, which is trying to be blue, white and red, but is mostly blue.

    I appreciate the help, thanks!
  2. jcsd
  3. Jul 17, 2013 #2

    Simon Bridge

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    Remember your high-school science classes about primary colors of light?

    If the bulbs are not green, and the color is provided by the filter, then changing the filter may be an option. If they are green LEDs then a filter over the green will just make it a dimmer green or not show at all.

    Note - even hardwired lights can be swapped out - you just need a soldering iron.

    What happens when you put blue light through a red-only filter?

    How were the different colors done before?
  4. Jul 17, 2013 #3


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    The colour of an LED is determined by the chemistry of the semiconductor. It cannot be changed without changing the diode.

    E = h * u, where E is the energy in electron volts, u is the frequency and h is plank's constant.

    If the forward voltage at which the LED starts to radiate is Vfwd, and if my memory serves me right, then; Vfwd * (wavelength in nm) = 1270.
  5. Jul 17, 2013 #4
    There is no filter currently, only a clear "window" where the light shines through. The LED itself is green on these buttons. So I cannot add a filter to the "window" to change the color? It will only dim the bulb?

    I've heard of desoldering, but I don't really want to get anywhere near that. :)

    Is this rhetorical/sarcastic? I believe it is magenta, right? Or is that only by adding two colors, which is different from filtering?

    The left side and right side of the controls each has its own separate bulb. From the factory, each side had one white bulb with a green "bulb cover" to make the light on the button look greenish-white (similar to the green that I am trying to change now).

    I had an idea: what if I go back to pure white LEDs and then add the color paper where I want, in the color I want (since white is all colors, the filter will show the color I want in that spot). This will work at least for the red, white and blue temp. selector. Still doesn't fix the green buttons.
  6. Jul 17, 2013 #5


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    A green light only emits light in the green part of the spectrum.

    A blue filter only allows through light in the blue part of the spectrum.

    Since a green lamp produces no blue light the result of a green bulb and a blue filter is black.

    In practice a green lamp will produce some blue light but not much or it would look bluey-green without a filter.
  7. Jul 17, 2013 #6
    So, basically the only way I can get the color I want without changing the blue bulbs would be to add a bulb of a specific color to the area where I want it.

    Thanks for the help, now to go back to the drawing board!
  8. Jul 17, 2013 #7

    Simon Bridge

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    That would be your most practical way forward ... the only practical way to change the color of the green lights is to replace them.

    For completeness - I will never use sarcasm in response to a question. That pretty much goes for almost all the people who answer questions here: it would defeat the purpose of the forum.

    My questions are suppose to act as a guide to your thinking - see how your mind latched on to a more workable solution? They are also a probe: as your answers will tell us about how you understand the subject, so we can tailor replies better to your need.

    The colored plastic or whatever between you and the source is a filter - filters work by only passing a limited part of the spectrum. A red filter only passes red etc. In practice they pass a bit of other colors too but a good red filter will pass none of the blue light - you may as well put a bit of heavy card in the way. When someone says the color is "black" they just mean that no light gets through.

    It is when you mix blue and red that you get magenta.

    You'd probably benefit from a refresher on light and colors - it will deepen your understanding of what you are doing.

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