expert at aspectled Written by Marty Lemke | A Leader in LED Technology

RGB is an acronym and stands for Red, Green, and Blue. These are three light colors that can be mixed together in different amounts to make up all the colors that most people can see. The colors that most people can see are referred to as the full spectrum of visible light. You may recall learning from your kindergarten teacher that the primary colors were Red, Yellow, and Blue. You did not remember wrong! To understand why we use green instead of yellow, let's look at two examples of mixing colors.

Sample A

In Sample A we will look at the three Primary Colors we learned in school: Red, Yellow, and Blue. If we mix adjacent colors we get the secondary colors Orange, Green, and Purple and if we mix the three together the paint color looks dark brown almost Black.

Sample B

In Sample B we will look at the 3 colors used in multi-colored lights: Red, Green, and Blue (RGB). If we mix the adjacent colors in this sample, we get Yellow, Magenta, and Cyan. When we mix these 3 colors of light together, we actually get White Light!

What is happening?!

You may have noticed a major difference between A and B: A is "paint" and B is a light. This difference is the key to why the mixing is different. In the paint example, we are not looking at the source of the light. We are looking at a reflection of the light.

If you paint a red swatch and look at it, what you are seeing is white light reflected off the object. The rest of the color wavelengths of the white light are absorbed by the object and only the red is visible. If you are looking at a black object, then all the color wavelengths are absorbed, and none are reflected.

The method of mixing in Sample A is called "Subtractive." It is the primary method used to convey color on printed materials. In Kindergarten, we learned the primary colors- these are simplifications. In the print industry, they use CMY which stands for Cyan, Magenta, and Yellow. They also often add in Black which is represented by the letter K.

Wait, why not Red, Blue, and Yellow?

Children are taught Red and Blue because these colors are more relatable to the real world. Cyan and Magenta are not as relatable but far more accurate in print media. Yellow is very relatable.

Now let's discuss Sample B. In this sample, the LEDs are the source of the light, not a reflection. You are looking directly at the energy coming out of its source. This is the basis for the second method of mixing colors- it is called "additive" mixing. Red, Green, and Blue can be combined in different ratios to make nearly the full spectrum of White Light. Due to the limitations of manufacturing, there are limits as to how pure this mixed white light can be. Because of this a fourth LED is sometimes added, and that is a dedicated, pure, "full spectrum" White Chip. Instead of using independent Red, Green and Blue channels, an LED in the lower wavelength spectrum (near blue) is coated with phosphors that emit white light when energized. With the addition of a dedicated white LED, W is added to the acronym, and the fixture or Strip Light is labeled as RGBW.

Perception Explained

The average Human Eye has 6 million receptors that perceive light and colors. These receptors are called Rods and Cones. Rods do not receive color; they only perceive light intensity. The cones are what see the colors. We have something called Trimetric Vision. There are specific Cones that see exclusively Red, Green, or Blue. S Cones perceive short wavelength light which corresponds to blue wavelength. There are fewer of these cones. M Cones correspond to green wavelength in the medium spectrum, and L cones correspond to Reds- the higher wavelengths of visible light.

These cones have a protein called photopsin that absorbs or filters the light just like the pigments in sample A. When you look at a red paint swatch, you see reflected light where the Cyan and Yellow are absorbed, and only red is seen. If you look at a Red LED, you are looking directly at the source. All this information is conveyed to the brain, and we perceive the color.

In Summary

There are two ways we perceive light: Reflected Light and Sourced Light.

Reflected material mixing is called Subtractive mixing and uses the colors CMY (and sometimes K for printing) It is based on the principle that reflected materials absorb light and only reflect certain wavelengths.

Sourced Light mixing is called Additive mixing and uses the colors RGB (and sometimes W) and directly mixes the light as we see it in our eyes.

LEDs are a source of light, and the letters RGB indicate the colors available to be mixed using the Additive mixing method.