I'm an electrical engineer tinkering with a tiny display that has an LED back light. It looks like a little square and it quickly cycles through red, green, blue light to produce the final display. I wanted to do some experiments to improve the brightness so I first researched how to design LED backlights but then I thought maybe I can just make a tiny light projector? And that might be easier to put together on the bench myself.

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I'm concerned about a few things. The LEDs will be physically close but can't all be at the center of the collimating lens. I don't want any hotpsots just a clean block of light like the original LED backlight which is why I thought of the diffuser. So maybe this is a bad idea? And of course I worry about all the things I don't know :)

Does this approach seem reasonable? Does the LED placement matter as much as I think it might? I'm thinking I can just look up collimating lenses at Edmunds but is there anything special I have to think about for the LED output pattern and lens combo?

  • $\begingroup$ Your projector (assuming a perfect lens and point-like R/G/B crystals) will collimate your LEDs, but the collimated rays from R/G/B crystals will go in a bit different directions, so that at a large enough distance you'll get three spots: red, green and blue—instead of a single white spot. This is simply because of different positions of the crystals with respect to the optical axis of the lens. $\endgroup$ – Ruslan Dec 12 '20 at 22:02

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