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Ask MAKE is a weekly column where we answer reader questions, like yours. Write them in to mattm@makezine.comor drop us a line on Twitter. We can’t wait to tackle your conundrums!

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Jacob asks:

I’m new to electronics, and am interested in LEDs. One thing I can’t figure out is why some of them are colored, while others are clear. What’s the deal with that?

Hey, good question! I’d never actually thought about it before, and now that you mention it, it does seem a bit confusing. My initial guess was that the coloring might be used as a filter to block out other colors, but that doesn’t make sense- in general, LEDs put out a very narrow spectrum of light, so they shouldn’t need filters (and it would probably be difficult to build a filter with that narrow of a cutoff range). One exception would be more complicated LEDs such as white ones, which normally start with blue light and then use a phosphor to convert it to white light. It seemed possible that at least for those, the color could be part of the phosphor- except that white LEDs are almost always clear! Besides, the phosphor part turns out to be located right on top of the dye.

So, the best I can tell is that the tinting is added to make it easier to tell them apart when they are off. The clear ones are a pain to sort out, because you have to plug them in to figure out what color they might be. Kind of funny, but I guess that’s how it goes!


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Comments

  1. oskay says:

    The question was, why are some of them *colored*? Tinted doesn’t necessarily mean the same thing.

    * A LED lens color is often milky white or water clear– milky white diffused lenses are sometimes said to be colored white. Diffused lenses are sometimes tinted, and diffused lenses are sometimes white in color. Clear lenses are also sometimes tinted or “water clear.”

    * Diffused versus clear lens:
    — A clear lens acts as, well, a lens, to project a spot with a fairly narrow beam of light. These ones are best for viewing from a large distance, or for illumination. You’ll commonly find these on traffic signals and outdoor signs and LED flashlights.
    — Diffused-lens LEDs emit their light over a wider angle, rather than projecting a narrow spot. These are most often used for indoor data displays and panel indicators. Diffused lenses are less useful outdoors because direct sunlight can “light up” the diffused plastic just as well as the LED element.

    *For diffused lenses, there’s a good argument from tinting aside from telling them apart by color: Diffused lenses emit a fair amount of their light sideways. If you have neighboring diffused LEDs of different emission colors, the color effectively “bleeds” into the diffused plastic of neighboring LEDs. Using tinted, diffused lenses can cut down on this effect.

    *An entirely separate use of tinted lenses is for color adjustment in (for example) white LEDs. Most white LEDs consist of a blue LED element with a wide-band emitting yellowish phosphor on top; you can see the phosphor layer if you look in the top of a clear-lens white LED. Some LED configurations like this use a yellow plastic lens to further shape the color profile to true white.

    *A third, common use of lens tinting is to increase contrast. When it’s off, a red-tinted (for example) LED lens can look much darker than an untinted LED lens.

    1. Matt Mets says:

      Thanks for the excellent clarifications, I had completely forgotten about the diffused case. The contrast ratio and color balancing (for indirectly colored LEDs) makes sense as well.

  2. amasci.com says:

    Eh, it’s just to increase contrast.

    Ideally an LED should appear black when off, bright when on. A dye which passes only LED-reddish light and blocks other colors will look red, not black.

    Plus there’s the psychological effect: ease in telling the difference between a turned-off device, versus a device which lacks LEDs. Clear LEDs are visually difficult to identify when inactive, so you might not be sure that an inert device even has any LEDs. But with red or green LEDs, you can visually locate the inactive lamps quite easily.