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Although this question is more of an optics than electronics, it strongly involves LEDs so I think it is a good idea to post it here.

I have a simple 3W, RGB LED with a 5deg lens. Everything is connected and and works but when projecting the light on the wall I can easily see the 3 different colors. I tried using a diffuse lens with partial success as the color mix inst 100%.

Is there any way to fully mix the colors of a standard 3W RGB LED?

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    \$\begingroup\$ I had this problem when I was making a propeller display, we bought some clear lens \$\endgroup\$ – Rick_2047 Nov 8 '11 at 14:30
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    \$\begingroup\$ You might use an array of lower-power LEDs, that way the colors will be both interleaved and closer together, hence easier to diffuse. \$\endgroup\$ – Ben Voigt Nov 8 '11 at 15:39
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    \$\begingroup\$ Clear lens multicolor LEDs are meant to be used with an external diffuser like a light pipe. Also, when using the diffuse lens, make sure the red, green, and blue levels are balanced with respect to each other, or one or two colors will dominate. \$\endgroup\$ – Mike DeSimone Nov 8 '11 at 15:49
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I had this problem when I was making a propeller display. We bought some clear lens leds but we were getting this same problem. More precisely, the cause is that there are 3 physically different LEDs inside the package. Now there are two options which worked for me. (But take all of this advice with a grain of salt since I worked on simple 5mm low power LEDs, as the size and power goes up things change.)

  1. Change the LEDs and get diffused lens ones. Like this here. I really don't know why someone would want a clear lens one. But I don't know much about optics. If you are really careful you can just use sandpaper to make the outer surface diffused, but I would not advise that, since I damaged some LEDs by doing that, before I got good results.

  2. Another way is to use something to diffuse the light. I know you used lenses but those worked for me, and I don't know why they didn't work for you. Maybe a pic showing your setup would give us a clearer idea. I got good results with covering them with a little butter paper. Normal paper could be used, but of course that will dim the lights way too much.

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  • \$\begingroup\$ Thanks for your response. The LED I'm using is much bigger than a 5mm LED, you can easily see the 3 emitters sitting one beside the other. Before I try to sand paper the lens or other custom technics I'm looking for a 'shelve solution'... \$\endgroup\$ – Gilad Nov 8 '11 at 15:34
  • \$\begingroup\$ (...four years later...) @Rick_2047 Did this actually work for you? I'm looking to roll my own dimmable LED-wifi bulb using a spark.io photon module. edit I should specify that I would like to use 3 separate LEDs, (r,g,b)... is that a silly idea? \$\endgroup\$ – Miles Alden Feb 22 '15 at 19:30
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A clear LED TIR lens will preserve the angular properties of the emitter through the optical system. In an RGB LED, all 3 colors can't be dead center at the same time. Two or all three will be off center. In effect, the lens will take the 3 colors and project "an image of them" up on the wall.

There are two ways to minimize this effect. One is to place the emitters as close together as possible. It sounds like you have a multi-die emitter with all 3 LEDs on the same chip. You can't get them any closer together than that.

The other is to diffuse the light, thereby mixing the colors. You are bound to lose some lumens when you diffuse the light.

There are a number of color-mixing LED lenses available from various manufacturers. For the best result, you need a lens that is designed specifically for the LED you are using. There isn't really any "standard 3W RGB LED" when it comes to optics. Here is one example of an optic designed for a specific RGB LED: http://search.digikey.com/us/en/products/CA10944_RGBX-MC-M/711-1146-ND/2354660

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You may try to "condition" the light as it were by passing the output of all three emitters through a light guide such as a transparent acrylic rod (sold online very cheaply). But I would say that a rather considerable length may be required to properly mix the colors. Don't know if your project allows for a 6"-8" rod attached vertically to the LED but it it does, it may actually help. Also, a quick note about "simple 3W, RGB LED" - there's nothing really simple about any 3W LED, let alone RGB. Just the difference between the forward voltages and driving currents mixed in with different sensitivity of human eye to different colors can drive you crazy. Anyway, assuming you have a proper controller for the RGB LED, it looks like this device was designed for architectural/landscape lighting and so the colors would only mix properly if projected 4'-6' out or even further. If yours is an indoor application, maybe you can locate three separate red, green and blue LEDs that would let you put them closer together to achieve better color mix at the distance you need?

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