White light is created by combining light of different wavelengths across the visible color spectrum. There are three primary light colors that combine to make white light: red, green, and blue. When red, green, and blue light are mixed together equally, they produce white light.
The Primary Colors of Light
The primary colors of light are red, green, and blue. This is different from the primary colors of pigment (paints and dyes), which are red, yellow, and blue. With light, the primary colors are those that align with the peak sensitivities of the three types of cone cells in our eyes that allow us to see color.
When all three primary colored lights are combined, they stimulate all three types of cone cells equally, creating the perception of white light. Here’s a quick overview of the primary light colors:
- Red light – Wavelengths around 700 nm
- Green light – Wavelengths around 546 nm
- Blue light – Wavelengths around 435 nm
These three colors of light correspond roughly with the colors detected by our L, M and S cone cells in our eyes. When combined equally, they produce additive mixing to form white light.
Additive Color Mixing with Light
With light, combining colors uses the principle of additive color mixing. This means that when different colored lights are combined, they produce a cumulative effect and all the wavelengths are present in the resulting light.
For example, when red and green light are mixed together, the result is yellow light. This is because red light wavelengths around 700nm are combined with green light wavelengths around 546nm. Both sets of wavelengths are present in the resulting yellow light.
In contrast, when pigment colors like paints mix together, the pigments absorb certain wavelengths and subtract out parts of the spectrum. This is called subtractive color mixing.
Since mixing light is additive, the combination of the primary red, green and blue lights results in a light source with all visible wavelengths present. This stimulates all three cone cell types in our eyes equally and is perceived as white light.
Mixing Ratios to Create White Light
To create white light from the primary colors red, green and blue, they need to be present in the right proportions. Each primary color contributes a range of wavelengths, and when balanced correctly, the sum of these results in white light.
There are a few common mixing ratios that can produce white light using the primary colors:
| Red | Green | Blue |
|---|---|---|
| 1 | 1 | 1 |
| 3 | 6 | 1 |
| 7 | 4 | 1 |
As you can see, as long as the proportions keep the contribution of the primary wavelengths in balance, the result is white light. Many white light sources use different ratios to achieve this balance.
Real World Examples of Combining Light to Make White
Understanding that combining red, green and blue light makes white helps explain how many white light sources work. Here are a few real-world examples:
Computer/Phone Screens
LED and LCD screens like those used in phones, computers and televisions use clusters of red, green and blue LEDs (light emitting diodes) to create all the colors on the screen. By turning on the red, green and blue LEDs to full brightness, the screen displays white.
RGB Stage/Studio Lights
In theater, studio and concert productions, RGB stage lights use red, green and blue colored lamps that can be mixed to produce white light. The lighting designer can control each color’s brightness to create the exact shade of white needed for the scene.
White LED Light Bulbs
LED light bulbs designed to produce white light use blue LEDs coated with a yellow phosphor. The blue LED light mixes with the yellow light from the phosphor to create white light. Varying the ratio of blue light to yellow phosphor gives different color temperatures of white, from warm (yellowish) to cool (bluish).
Fluorescent Lights
Inside a fluorescent light tube, mercury vapor emits ultraviolet light when electrically stimulated. This UV light causes a phosphor coating inside the tube to glow and emit visible light. Different phosphor blends emit red, green and blue wavelengths that mix to form white light.
True White Light vs Mixed Colors
It’s important to understand the difference between true white light and the perception of white created by mixing colors. When red, green and blue combine in the right balance, they produce a light source with a continuous spectrum we see as white. This is true white light.
However, it is also possible to mix colors that merely appear white to our eyes while not having a full spectrum. For example, mixing complementary colors like yellow and blue can appear white but this is not true white light. These mixes will not render colors the same way as a full spectrum white light source.
True white light can only be created by sources emitting a balanced combination of red, green and blue wavelengths of light. This stimulates our eye’s cone cells evenly, giving the perception of white while also providing a continuous spectrum to properly render colors.
Human Color Vision and White Light Perception
Our ability to perceive white light when the primary colors are mixed comes down to the biology of our visual system. Human color vision relies on three types of cone photoreceptor cells in the retina of our eyes:
- S cones respond to short wavelength blue light
- M cones respond to medium wavelength green light
- L cones respond to long wavelength red light
These cone cells send signals to the visual cortex of our brain, which interprets different levels of stimulation as different colors. When all three types of cones are stimulated about equally, our brain perceives this as white light.
This is why combining red, green and blue light creates white – the mix of wavelengths stimulates the S, M and L cones equally. Other animals with different vision may not perceive the same mix as white.
Mixing Light Colors in Photography
In photography and film, controlling color and light is crucial for getting the right look. The principles of mixing red, green and blue light are applied here as well.
In film and digital cameras, photosites on the sensor detect amounts of red, green and blue light. Color film works similarly, with layers of dye reacting to red, green and blue wavelengths.
When shooting under white light sources or daylight, all three colors are balanced and mix to create white. But for creative color effects, photographers use techniques like color filters to shift the balance of RGB colors or gels on lights to tint scenes.
Understanding how cameras detect color reinforces that mixing red, green and blue makes white light visible in photos.
Other Additive Color Mixing Systems
The red, green and blue primary color system used for light and computer displays is not the only additive color model. Here are some other examples of using primary colors of light to create white:
RYB Color Model
The RYB color model uses red, yellow and blue as the primary colors. Mixing wavelengths from these sources can also produce white light, though not as efficiently as RGB.
CMY Color Model
The CMY model uses cyan, magenta and yellow as the primary colors. This is subtractive color used for pigments, but the complement of CMY is RGB, so mixing CMY light creates white.
RGBW LEDs
Some LED light bulbs add white LEDs along with RGB diodes. The white helps create better quality and more natural white light compared to RGB alone.
While these other systems can also mix to white, the red, green and blue primary system aligns best with human vision and is most widely used for lighting, displays and photography.
Converting Other Colors to RGB Values
To work with color digitally on screens, image files use RGB color values. Each primary color is assigned a brightness value from 0 (no light) to 255 (maximum brightness).
Any color can be created by mixing amounts of red, green and blue light. Converting real world colors to RGB values is done by measuring the levels of red, green and blue light reflected from the color:
| Color | R Value | G Value | B Value |
|---|---|---|---|
| Red | 255 | 0 | 0 |
| Yellow | 255 | 255 | 0 |
| Green | 0 | 128 | 0 |
White in RGB is R255, G255, B255 – full brightness for all three primary colors. Black is the absence of light, R0, G0, B0.
Understanding how real colors convert to combinations of red, green and blue improves digital image manipulation using photo editing software or design tools.
Limitations and Issues with RGB White Light
While combining red, green and blue light is the primary way to create white light, RGB technology has some limitations:
- Can’t produce very deep blacks or very bright whites
- Emitting pure primary wavelengths is difficult
- Blue light fades over time
- Not as energy efficient as other light technologies
This has led to the development of more advanced display and lighting innovations like quantum dot and OLED technology to improve on RGB color mixing.
There are also other factors like color temperature that affect white light quality for visual tasks. RGB alone can’t guarantee perfectly natural white light.
Conclusion
When mixed together in the proper proportions, red, green and blue light combine to produce what we perceive as white light. This is due to how our eye’s cone cells respond to wavelengths across the visible color spectrum.
Understanding the principles of additive RGB color mixing helps explain how many display, lighting and photography technologies produce white light. While RGB has limitations, it remains the primary way to produce white light from mixing primary colors.
