The primary colors of light are the set of colors that can be combined to produce all other colors in the visible light spectrum. Unlike paint pigments, where the primary colors are red, blue and yellow, the primary colors of light are red, green, and blue. This is because the way light mixes together is fundamentally different from the way pigments mix. When different colored lights shine on the same spot, the light adds together to produce different colors. So by mixing red, green and blue light in different proportions, we can create any color that the human eye can perceive.
This means that any color that is not red, green or blue cannot be considered a primary color of light. The non-primary colors include yellow, cyan, magenta, orange, violet, brown, etc. While these colors can be produced by mixing the primary colors, they cannot be used as primaries themselves to produce all the other colors. Understanding the primary colors of light is important for many applications such as TVs, computer monitors, theater lighting, photography and more.
How Light Mixing Works
To understand why red, green and blue are the primary colors of light, we need to understand how light mixing works. When two or more lights shine on the same spot, the light waves add together. Light waves have crests and troughs just like ocean waves. When two lights waves overlap, the crests stack on top of each other making brighter light, while troughs cancel out crests making darker regions.
This additive mixing means that as more colored lights are combined, they make increasingly lighter and brighter shades. Eventually adding three primary colors at full intensity results in white light. The primary colors of light are defined as the minimum set of colors that can be mixed to produce white light.
Why Red, Green and Blue are the Primaries
Red, green and blue correspond to the three types of color sensitive cones in our eyes. We have cones that are most sensitive to long wavelength red light, medium wavelength green light and short wavelength blue light. By stimulating these three cone types in different combinations, all the colors we see can be produced.
So red, green and blue are the primary colors of light due to the biology of human vision. They directly correspond to the three types of cones responsible for color vision. This is the fundamental reason why RGB are chosen as the primary colors in many color systems and technologies.
Examples of Light Mixing
Here are some examples of how the primary colors can be mixed to create other colors:
| Colors Mixed | Resulting Color |
|---|---|
| Red + Green | Yellow |
| Red + Blue | Magenta |
| Green + Blue | Cyan |
| Red + Green + Blue | White |
As shown, combining two primary colors creates a secondary color. Cyan, magenta and yellow are called the secondary colors. Mixing all three primaries produces white light. Varying the proportions of the primaries creates all the colors of the rainbow.
Primary Pigment Colors vs. Primary Light Colors
The primary colors of pigments are different from those of light. Pigments work by absorbing certain wavelengths to subtract color. The primaries are defined as the colors that can absorb two primary light colors. The pigment primaries are magenta (absorbs green), yellow (absorbs blue) and cyan (absorbs red). This subtractive mixing model gives different primaries than the additive mixing of light.
Applications Using RGB Primaries
The RGB color model has many practical applications based on the red, green and blue primary colors of light:
- Computer/TV monitors use red, green and blue phosphor dots to produce all on-screen colors.
- Digital cameras use RGB color filters over image sensors to capture a broad range of colors.
- LED lighting systems mix red, green and blue LEDs to create customizable lighting.
- Stage/theater lighting uses RGB filters and gels to produce dramatic colored lighting.
In print and painting, other primaries like CMYK are more useful. But for any application involving light emission to generate a range of colors, RGB are the primary colors to use.
Non-Primary Colors of Light
So which colors are not primary colors of light? Here are some examples:
- Yellow – Made by mixing red and green light.
- Cyan – Made by mixing green and blue light.
- Magenta – Made by mixing red and blue light.
- White – Made by mixing red, green and blue light.
- Orange – Made by mixing red and some green light.
Any color that can be created by mixing the primaries cannot itself be a primary color. This includes the secondary colors, the tertiary colors like orange and chartreuse, and neutrals like white, black and greys.
The only colors that qualify as primary colors are the red, green and blue wavelengths of light. These primaries allow all other colors to be generated through additive mixing.
Overlapping Wavelengths
In reality, the lines between spectral colors are blurred. Red, green and blue light have broad wavelength ranges that overlap. For example, cyan light stimulates both the green and blue cones somewhat. So cyan is not a pure secondary color. But the “pure” primary and secondary colors are still useful for understanding color mixing.
Other Primary Systems
RGB are not the only choice of primary colors. Some other color systems use different primaries:
- RYB (red, yellow, blue) – Used historically by painters.
- CMYK (cyan, magenta, yellow, black) – Used for color printing.
However, RGB is the most common choice of primaries for applications related to light and displays. Red, green and blue directly align with the human visual system.
Conclusion
In summary, the primary colors of light are red, green and blue. This is because these colors correspond to the three types of cones in our eyes, allowing the widest range of colors to be perceived through additive mixing. No other set of primaries can produce the full gamut of colors through light mixing. All other colors not in the red, green and blue wavelengths are non-primary colors, including cyan, yellow, magenta, orange, violet, etc. Understanding additive color mixing is key to producing color in many optical applications.
