When mixing colors, people usually picture paint, but mixing light is fundamentally different from mixing physical materials. The result of combining red, green, and blue (RGB) depends entirely on whether those colors are sources of light or pigments. Light is electromagnetic radiation perceived in the visible spectrum, and the interaction of color wavelengths dictates the final color we see. Understanding this distinction is key to understanding the physics of color perception.
The Result: White Light
When red, green, and blue light are mixed together in equal proportions and at full intensity, the resulting color is white light. These three colors are considered the primary colors of light. By combining the full spectrum of light wavelengths they represent, the mixture effectively creates the same perception as natural daylight.
Understanding Additive Color Mixing
The scientific principle at work when red, green, and blue light are combined is called additive color mixing. This process involves physically adding different wavelengths of light together, which increases the total light energy perceived by the eye. When light sources overlap, their spectral components merge, and the resulting light contains all the wavelengths of the original sources. The human eye perceives color using cone photoreceptors sensitive to short (blue), medium (green), and long (red) wavelengths of light.
When red, green, and blue light are projected together, they stimulate all three types of cones simultaneously and equally. The brain interprets this balanced stimulation as white light. Combining only two primary colors creates secondary colors: red and green make yellow, green and blue make cyan, and red and blue make magenta. In the additive system, the resulting color is always lighter than the individual source colors.
Why Pigments Are Different
The common confusion about mixing red, green, and blue stems from physical materials like paint or ink, which follow subtractive color mixing. Pigments do not emit light; instead, they absorb (or subtract) certain light wavelengths and reflect the rest. When mixing paints, each pigment continues to absorb its specific wavelengths, meaning the combination absorbs more light overall.
For example, a red pigment absorbs blue and green light, reflecting only red wavelengths. When mixed, the resulting material absorbs nearly all visible light wavelengths, reflecting very little back to the eye. This process subtracts light, leading to a darker color that tends toward black or dark brown. The primary colors for pigments, used in printing, are cyan, magenta, and yellow (CMY), which, when combined, theoretically produce black.
RGB in Digital Technology
The principle of additive color mixing is the foundation for almost all digital displays, including television screens, computer monitors, and smartphone displays. These devices use the RGB color model to generate millions of colors from only three light sources. The screen surface is composed of millions of tiny elements called pixels, each made up of three sub-pixels: one red, one green, and one blue light emitter.
By controlling the intensity of light emitted by these three sub-pixels, the device can produce any color within its spectrum. To display a fully saturated white, all three sub-pixels are illuminated at their maximum intensity. When all three sub-pixels are turned off, the pixel appears black, representing the absence of light emission. The proximity of these tiny colored lights causes the human eye to blend them into a single perceived color, making the RGB model the standard for displaying visual content.