White light is made up of a combination of all the colors of the visible light spectrum. When red, green, and blue light beams are mixed together, they produce white light. This is known as an additive color model, where combining different colored lights results in brighter, lighter colors. Understanding the basics of how light and color work can help explain why red, green, and blue are the primary colors of light that combine to make white.
The Visible Spectrum of Light
The visible light spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. The wavelengths of visible light range from about 380 nanometers (violet) to about 780 nanometers (red). Within this range, there are a continuum of wavelengths that correspond to all the colors humans can see.
When white light passes through a prism, the different wavelengths separate into the familiar rainbow pattern of colors. This ordered arrangement of colors from shortest to longest wavelength is known as the visible spectrum. The sequence of colors includes violet, indigo, blue, green, yellow, orange, and red.
Each color has a different predominant wavelength range. For example, blue light is between about 450-495 nm, green light is between 495-570 nm, and red light is between 620-750 nm. When all these wavelengths strike the eye at the same time, the brain perceives the combined color as white.
Primary Colors of Light
There are three primary colors of light that can be combined to create all other colors: red, green, and blue. This is called the RGB color model. Television and computer screens create color by combining different intensities of red, green, and blue light.
This is different from paints and pigments, where the primary colors are red, yellow, and blue (RYB). This is known as a subtractive color model, where combining paint colors results in darker, duller colors as more is subtracted from the light. Light works in the opposite additive way, starting with darkness and adding different colors of light to create brightness and new hues.
Red, green, and blue are the primary colors of light because they correspond to different cone photoreceptor cells in our eyes that detect those wavelengths. The cones send signals to the brain that are interpreted as color. When red, green, and blue light enters the eye at the same time, the cones are stimulated evenly, leading to the perception of white.
Combining Red, Green, and Blue Light
When beams of pure red, green, and blue light are overlapped, they combine additively to produce white light. This can be demonstrated with a red laser pointer, a green laser pointer, and a blue laser pointer. When their beams are overlapped, the spot will appear white where all three colors mix together.
This additive mixing of light can also be seen with color stage lights. Using just red, green, and blue gels over the lights allows a lighting designer to create almost any color by adjusting the brightness of each light. Where all three overlap at full intensity, the result is white light.
On a pixel level, LED and LCD screens work the same way. Tiny red, green, and blue subpixels combine in clusters to produce colors. When the red, green, and blue subpixels are turned on at full brightness, that pixel will appear white.
Proportions of Red, Green, and Blue Light
In order to make white light, red, green, and blue light must be present in the proper proportions. If one color dominates, the light will take on that hue. The exact ratio depends on the primary colors used.
For computer and TV screens, the balanced ratios needed to produce white light are roughly:
- Red: 0.30
- Green: 0.59
- Blue: 0.11
This means for every 1 part blue, there needs to be approximately 3 parts red and 5 parts green to make white. However, these proportions can vary based on the specific primary colors used.
Other Color Combinations Producing White
While red, green, and blue are the primary colors that combine to make white light, other sets of colors can also produce white through additive mixing:
- Cyan, magenta, and yellow
- Red, green, and blue-green
- Red, blue, and green-yellow
However, red, green, and blue remain the standard primary colors for light and are capable of producing the widest range of hues through different combinations.
Conclusion
White light is composed of a balanced mixture of the primary colors of light: red, green, and blue. This is due to the additive mixing of light, where combining colors results in brighter, lighter hues. Red, green, and blue correspond to the different color cones in our eyes and stimulate them evenly to be perceived as white light. Understanding the basics of light color mixing provides insight into how display screens, projectors, and other technologies produce color from the primary red, green, and blue components.
