[SOLVED] White light from RGB LEDs

[d123]

Hi,

Is it possible to get white light, like a true white LED gives out, from average-cost/cheap RGB LEDs and a static voltage source (not PWMing the LEDs in the RGB LED) with trimpots to vary the current to each colour in the RGB LED, or is the result always something rather turquoise in colour or predominantly red?

Comparing a white LED to my attempt, the results were horrible and not at all white.

I used about 10mA for the green and for the blue LEDs and from 1mA to 6mA for the red one. The RGB LEDs are common cathode, in case that matters.

I read about it briefly, sounded hard to get right, messed around with one RGB LED and can't get anything like white light from one.

This is only curiosity.

Thanks.

 

[KlausST]

Hi,

I'd say no.
Do you know about CRI. Read about it.
Read about spectral distribution of sunlight, halogen light, RGB light...

R G B are LEDs, LEDs send out relatively narrow color bandwidth.
So if you mix RGB, then there are deep valleys in frequency band.

The result will be that white areas may look like white,
but when you compare a picture with many different colors under RGB light and under true white light,
then you will see brightness errors under the LED light.
--> Missing light source colors

Klaus

 

[dick_freebird]

There is also likely to be an imbalance between R, G, B
intensity as they are three different materials, unless
there was care taken to make them equal, to the eye.
And the eye has its own color-sensitivity-curve as well.

 

[Audioguru]

Look at a white LED when it is off, it looks yellow. That is the phosphor that is in top of the blue LED. Yellow light from the phosphor has red and green in it.

 

[c_mitra]

For general applications, you will be fine to use RGB led as a white light source.

For example, we see only three colors, R G and B. The eye has three kinds of sensors. All colors (other these primary colors) are mixed colors.

And the color TV also has three basic phosphors and all other colors are mixtures. And the color films and photos - and the wonderful printouts.

But white light, say sunlight in a shade, is NOT a mixture of three colors: R G and B. It has a continuous spectrum.

In the spectrum of the sun light, yellow is a monochromatic color. But we see it as a mixture of red and green!

And add to this mess: different people see the same color differently. Some people call the sodium D lines (sodium vapor lamps) as yellow but some see it as orange.

But artists and painters have taken this to the extreme: the painting does not look the same in the studio and at home! Lighting matters.

So it all depends. What is the final use. If you are drawing a painting, forget about LED RGB: walk outside and stand the shade. Daylight is the best. But if you are just interested in street lighting, then you just go ahead!