How to difuse, colour mix RGB Power LEDs for spot lighting?

[Joern]

Hi guys, my self-made ambient light system is on its way and I've been enjoying my prototype on my desk for quite some time now.

But one of my current issues is creating a spot lighting to walls or the ceiling instead of having a bare LED emitter that blinds everyone in the room.
It should mix the RGB lights as smooth and evenly possible for good colour mixing. For the time being, I just screwed off the reflector of my flashlight and put it on top of my RGB LED.
It's totally wonky, but works quite ok, though you can still see patches, where the red, green and blue lights don't mix properly.

I just received my order of LED optics in 30, 45 and 60 degree. They fit very nicely on top of my LED but other than that, it's a total failure. The optics don't mix RGB colours at all and simply project big red, green and blue patches onto the wall. (Neither do they force the light into given degree rays.) This is the 45° for example: https://www.fasttech.com/products/1108206

How can I create a smooth colour blend? Are there any affordable (less than $2 each) optics for colour mixing RGB LEDs?
The only solutions that come to my mind now are sanding off the LED emitter with sand paper for light diffusion and getting flashlight reflectors like those from Fasttech ( http://www.fasttech.com/category/1617/diy-kits-parts-reflectors/ ) to create spot lighting.

But I have my doubts that those reflectors fit onto the LED very well.

Any advice?

This is how my emitter is mounted:

With flashlight reflector

 

[SemiMan]

Color mixing is difficult, especially if you are trying to achieve a spot. Very difficult actually without matching the LED and the optic.

The optic you linked to is designed for Cree LEDs .. which one of course is not defined. Obviously you don't have a Cree LED, but even if you did, you would still run into issues.

As you have found, reflectors are easier for color mixing. The best ones are multifaceted reflectors, but perhaps an orange peel reflector would accomplish a lot for you.

I am not aware of any specific color mixing optic for anywhere near $2 though, and specific color mixing optics are few.

Semiman

 

[RoGuE_StreaK]

Have you experimented with diffusing the emitter itself, just to see if it works? A quick and dirty experiment could be to cover the emitter in the likes of baking paper, just to see if that has any positive blending effect when the optic is jammed on. Don't power it for too long though, don't want to risk it catching fire (though I guess baking paper should be rated for heat)
If that does seem to work, I wouldn't recommend attacking the dome with sandpaper, you could instead try the spraycan "window frost", though no idea how it would chemically react to the dome (it's a film, not an etchant), or if it would stand up to the heat. Might be worth an experiment though.

Obviously you will lose a significant amount of light with this method.

 

[Joern]

Thanks SemiMan and Rouge Streak for your inputs!
I think I'll try orange peel reflectors then for some spot lighting - the optics I got don't accomplish much. The clear dome of the 3 Watt emitter is about 5mm in diameter, which is between an XR-E and XM-L / XR-C, iirc.
I found 2 aluminium reflectors which would fit, but they differ in size (diameter and depth)

I mostly have no idea, in what way those dimensions alter the light pattern. Could you hand me a recommendation of what would possibly provide good results for RGB LEDs?
depth 31mm, diameter: 41mm - http://www.fasttech.com/products/1220101
depth: 20mm, diameter: 20mm - http://www.fasttech.com/products/1209601

The current smooth reflector I use has the dimension: diameter: 25mm, depth 25mm - the colours aren't overlaid very nicely and actually have a large offset to each other, but it's been 'okay' for me.

@Rogue Streak, the baking paper was a great idea. It immensely improves the colour blending of the LED. You can say, the yellow is now actually yellow, instead of an orangy hue with a green blob in its center - or at least it is much much more subtle. I will try to look for some of that window frost spray. Might try to sand one of my emitters off as well though as I think it's still worth a shot. They were fairly cheap at $3 anyway and I still got a handful around.

 

[Harold_B]

I haven't tried this on a multichip LED but the way it is done in many DLP projectors that use individual RGB LEDs combined along a single optical path is to bring the RGB to close to collimation using a pair or aspheric lenses (for each LED in the case of the projector) and then doing the "color mixing" through a fly eye lens. Do a search for Texas Instruments DLP application notes if you are interested. Another option if you want to mold or cast your own silicone parts is to use a translucent silicone and make a mixing rod. A clear silicone or a Castable acrylic with polycarbonate balls, TiO2 or silicate powder works OK too. There's a thesis on this but I can recall the title.
The best solution I have found is a Dow Corning product MS-2002. A white highly reflective and diffusive material that was just released. You can find a blurb about it on the website but I'm not aware that anyone is selling individual components currently.

 

[robisais]

I think it's called a TIR optic. You can see a picture and description of it here

http://flashlightwiki.com/Lenses

The one on that page has a smooth front surface, the ones i saw in my fixture had very rough, bumpy front surfaces, probably to mix the light colors.

 

[robisais]

I think it's called a TIR optic. You can see a picture and description of it here

http://flashlightwiki.com/Lenses

The one on that page has a smooth front surface, the ones i saw in my fixture had very rough, bumpy front surfaces, probably to mix the light colors.