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: 
Imagine you have three LEDs (red/green/blue "RGB"). 

Each LED primarily stimulates a corresponding type of "cone" in the human eye as described [here](http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html#c1). 

![enter image description here](https://i.stack.imgur.com/fE0Xf.gif)

So a perceived color is created by a combination of the intensities from the three LEDs. If we include intensity of color as a discrete color, then for 1,000,000 colors we would need log2(10^6)/3 bits per color or about 7 bits per 'color'. 

Most likely they are using 8 bits PWM intensity per color (about 0.4% steps in intensity), giving 16,777,216 or 16 million 'colors'. In reality you are not going to be able to visually distinguish anything like that many, and many of the 'colors' are just different intensities of a color that is visually the same. 

White LEDs look yellow when not on- also some sources use a yellow component to the light to make the color appearance better for sensitive things like flesh tones and food (so they're [RGBY](http://www.pcmag.com/encyclopedia/term/61725/rgby) rather than RGB).
> 
> 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 ?
> 
> 
> 

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.