Purpose of Warm/Cold LED modules with RGB LEDs


RGBWW (aka RGBCCT or RGBCW) comes with cool & warm white temperature LEDs. Marketing states instead of standard 16M colors (2^8^3) that is now allows over 1T colors (2^8^5). Some even come with only a cool or only a warm white LED.

I don’t understand though, RGB can mix to form different temperatures of white on its own.

Televisions/computers/phones only use RGB (or BGR).

In: 6

The “white” you get from combined red green and blue LEDs is nowhere near as pleasant as a proper white led

LEDs for lighting need to be bright. In these conditions, you need a bright white light.

Simple math says red + green + blue gives you white light. But that’s just one white light’s worth of brightness. Okay, add another full white LED to get 2 white light intensity. Why not add a 3rd one to get more?

The downside is that the white light drowns out the saturation of color. The color isn’t as deep.

Certain TVs like the LG OLED panels also use a WRGB pixel arrangement to increase brightness. One of the downsides as mentioned before is that the colors are not as saturated.

One problem is that green leds aren’t perfectly green, so you can’t make perfect white with them. But even if they were perfect, there’s a difference between white that’s made up of 3 primary colors and white made up of a continuous spectrum of an infinite number of colors. Sure, both will seem white to your eyes, but once the light starts reflecting off of colored objects, you will see differences. This is even worse if you’re using the lights to record with a camera.

The reason you need “white” (be they warm-white or cool-white) LEDs for lighting, rather than just mixtures of RGB has to do with *colour-rendering*, or colour-rendering index (CRI).

Although you can make apparently the same colour of white light with a white LED or matching it with some mix of RGB, the white LED has a *broad spectrum* from red through to blue, whereas an RGB-mix only has wavelengths at very specific narrow Red Green and Blue wavelengths.

RGB-white is ok for a TV or display-screen, but when you use the light to illuminate real objects, such as people (skin-tone), upholstery, clothes, food, … the colours get distorted. Some fabrics or food will look dull and drab, and other colours (where the reflectance matches the wavelengths in the RGB LED) will “pop” and look gaudy and almost fluorescent (like the stage-lighting typically used for pantomime!).

(Source: I used to work in display-screen colour measurement)