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Thread: Mixing Luxeons to get white

  1. #1
    Flashaholic
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    Default Mixing Luxeons to get white

    Has anyone tried mixing red, green and blue Luxeon Star/Os to get white light?

    I am wondering if this is a lower power route to white-looking illumination.

    Steve

  2. #2
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    Default Re: Mixing Luxeons to get white

    Bandgap, you can get white alright (sometimes), but it won't be quite what you'd hoped for. Here are the problems you likely to face, in summary:

    - weird multi-colored shadows (very disturbing)

    - weird multi-colored coronas (also disturbing)

    - each color "shifts" differently over time and also with temperature, resulting in a changing shade of white. yes, depending on how hard you drive the LEDs, the color shifts as the light warms up...

    - the output of each color needs to be controlled and matched alongside the other colors - its a balancing act and all colors must be balanced simultaneously (can't do it one at a time - won't work). oh, and don't forget about that color shift when the light ages...

    - each set of RGB leds must be "calibrated" differently, particularly if you can't control the binning of what you get

    - perhaps surprising to some, but 3 white luxeons are brighter than an RGB combination. Most often, the red is the one letting team down.

    - driving the RGBs might be a problem too, reds tend to have very low Vfs (often less than 3V), while the other colors are usually more than 3V.

    Been there, tried that - I can say its TOUGH! And really not worth the time, which kinda explains why no one's gone ahead and taken this big time (other than for large-screens).

  3. #3
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    Default Re: Mixing Luxeons to get white

    Everything Leo said. I've been there, done that too. One curious consequence of the thermal effects that Leo mentioned is that these RGB "white" setups mimic incandescent lamps in one regard, as they are driven harder the light color shifts to the bluer end of the spectrum. The reason for this is that the output of the red LEDs falls off more rapidly with increasing temperature than that of the greens and blues.

  4. #4
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    Default Re: Mixing Luxeons to get white

    I wonder if side emitters would work?
    Take two reds, one green and a blue with Mad Max regulators to adjust them? It would take one heck of an optic to mix the lights together though.
    "What are you doing today"? "Calibrating my flashlight". That would be the sign of a deeply disturbed flashaholic! [img]images/icons/grin.gif[/img]

  5. #5
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    Default Re: Mixing Luxeons to get white

    Hotfoot said...

    - perhaps surprising to some, but 3 white Luxeons are brighter than an RGB combination. Most often, the red is the one letting team down.

    Ah, do you have figures, even approximate?

    Thanks to all for the notes on colour smoothness, but this is not too much of a problem, unless it is awful. Efficiency is the main thing for me with colour rendering second.

    I have peviously made a 'white' lamp from numerous amber 5mm leds, two greens and a blue. (Don Klipstein worked out the ratios of leds for me - so thanks go to him)

    Although the beam appeared somewhat mottled and ringed when shone at a white surface, colour was fine for a cycling front lamp, which is what I was making.
    Brightness was another thing, as I was too mean to pay for all the LEDs needed for enough light.

    Incedentally, on the subject of colour, although white Stars give a great light, some coloured things appear less visible than with a normal lamp which, I suspect, is due to the rather strange colour profle of white Luxeons.
    Or it could be my imagination.

    Steve

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