RGB wavelengths LED's

Can someone tell me in nm what the optimal three wavelengths are for RGB color?

I want to try simulating this on a small scale with three individual, high intensity LED's.

Second, related, question. Please excuse.

By varying the intensity of the three colors of LED's, I am looking to produce a seamless shift across the entire color spectrum.

What kind of dimming circuit would best suit this application? I have seen current based ones, but was wondering if some kind of PWM might be more linear.

Thank you kindly for any advice.

Ken Farrel

Reply to
Ken Farrel
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There are many meanings for "optimal" here - cost, color gamut, brightness, power consumption, size, lifetime, etc, and various coimbinations of factors.

Reply to
Richard Henry

Since you are talking about LEDs, you will have to work with what exists or else contract to get some existing LED 'pushed' a little one way or another. Keep in mind, LEDs emit over a broad range, not some narrow line. So human perception of all of that will need to be taken into account for what you are planning to do.

Some folks have already gone to some trouble to develop tri-color LED systems that achieve usable range of perceived color and high a fair degree of brightness, so that they can be used outdoors in broad daylight. Unless your needs are unusual, this is a market area you should examine to see what others have done here.

Understood.

The systems I've worked on use DACs to set an appropriate "white point" balance between the LEDs. This may be 100% or 25% or some other reference figure and the PWM is fixed during this calibration. But the idea is to tweak the white point to where you want it and then to PWM for brightness or for relative color change.

However, you will need to be familiar with CIE color curves and how to compute brightness and normalized (x,y) to use against your white point to generate an apparent hue. You will need to invert this process if you intend to drive the hue and need to develop (x,y) values to get there. That will probably involve a calibration step with your tri-color LED (can be performed at most any set PWM level -- even different PWMs for each color, if you like) to develop the matrix and then invert it for use.

I've done some of what you are trying to do in a practical system that met my needs.

No problem. I can recommend a book or two, if you are interested in human perception of colors and brightness. Lots and lots of research articles (some very fine ones from Edmund Land back around circa the last 1970s and early 1980s, if memory serves, too.)

Jon

Reply to
Jonathan Kirwan

I should have added that you don't have to do it this way. You can avoid the DAC, I think, and just calibrate the LED and its surrounding design (resistor and voltage supply, for example.) Then use that calibration step for the rest. You'll need to do that calibration anyway, I think, if you are really trying to accurately sweep the apparent hue in some designed fashion. If you don't really care about any of that and can tolerate just a sweep without any necessary similarity in one unit from another, then you can pretty much just develop some function that takes in a scalar value representing your current color point and that develops the three PWM values to use from a basis function chosen for mathematical simplicity.

Jon

Reply to
Jonathan Kirwan

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