Question: I see the Philips Hue and LIFX led bulb can generate the millions of colors, I can find ![enter image description here](https://i.stack.imgur.com/T7ovG.jpg).

can anyone tell me how this light works to generate millions of colors, what is the yellow LED light and white LED light, are they all the RGB led lights ? is each LED individually controlled by the circuit, and use all of them to make a color combination and is each LED controlled by simply opening/closing or dimming in different levels.

Thank you

Answer: 
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> can anyone tell me how this light works to generate millions of colors, what is the yellow LED light and white LED light, are they all the RGB led lights ?
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> 

The white LEDs are individual red, green, or blue LEDs as indicated by their silkscreen. The yellow LEDs are white LEDs; the yellow part of the LED is a phosphorescent material that absorbs high-energy photons (e.g. blue light) and emits lower-energy photons (e.g. orange-yellow light).

> 
> is each LED individually controlled by the circuit, and use all of them to make a color combination and is each LED controlled by simply opening/closing or dimming in different levels.
> 
> 
> 

It is very common to use [PWM dimming](http://en.wikipedia.org/wiki/Pulse-width_modulation#Power_delivery) in order to have fine control of a LEDs output; I have no proof that it is used here but that is very likely the case.
The connector in the center has four leads labelled "R", "G", "B" and "W".

So it's safe to assume that all red LEDs controlled by one signal (they work in unison). Same for the blue, green and white LED groups.

The traces seem to indicate that the LEDs for each color are connected in series.

Dimming LEDs by PWM is patented in some countries, so the dimming for each color could be achieved by by a very similar method, which is however sufficiently different from patent lawyer's perspective. Analog dimming is, most likely, not used as it would produce more heat in the driving electronics (and make them more complex; the controller circuit is digital anyway).