Color mixing depends on whether you are combining light that enters your eyes or materials that absorb and reflect light. Screens use additive mixing because red, green, and blue light sources add their intensities together. Paints, inks, and filters use subtractive mixing because pigments remove certain wavelengths from white light.
This difference explains why a phone display can make bright white, while mixing many paints often makes a dark brown or black.
Key Facts
- Additive mixing uses light sources: red + green = yellow, green + blue = cyan, blue + red = magenta.
- In additive RGB mixing, red + green + blue = white if the three lights have balanced intensities.
- Subtractive mixing uses pigments or filters: cyan absorbs red, magenta absorbs green, and yellow absorbs blue.
- In subtractive CMY mixing, cyan + magenta = blue, magenta + yellow = red, and yellow + cyan = green.
- Ideal subtractive mixing gives cyan + magenta + yellow = black because most visible light is absorbed.
- Visible light has wavelengths from about 400 nm to 700 nm, with violet near 400 nm and red near 700 nm.
Vocabulary
- Additive color mixing
- Additive color mixing is the creation of colors by combining different colors of light.
- Subtractive color mixing
- Subtractive color mixing is the creation of colors by using pigments or filters that absorb some wavelengths and reflect or transmit others.
- Primary colors of light
- The primary colors of light are red, green, and blue because they can be combined in different intensities to make many perceived colors.
- Pigment
- A pigment is a material that gives color by absorbing certain wavelengths of light and reflecting others.
- Complementary colors
- Complementary colors are pairs that combine to make white in additive mixing or strongly absorb each other in subtractive mixing.
Common Mistakes to Avoid
- Using the same primary colors for light and paint is wrong because light uses RGB additive mixing while pigments are best described by CMY subtractive mixing.
- Saying red and green always make brown is wrong because red and green light make yellow, while red and green pigments can absorb many wavelengths and look dull or brown.
- Assuming white is a single wavelength is wrong because white light is a mixture of many wavelengths or a balanced combination of red, green, and blue light reaching the eye.
- Thinking a blue object creates blue light is wrong because most blue objects reflect blue wavelengths from the light shining on them and absorb many other wavelengths.
Practice Questions
- 1 A screen pixel has red, green, and blue channels. If the red and green channels are each set to 80 percent intensity and the blue channel is set to 0 percent, what color should the pixel appear?
- 2 A cyan filter absorbs 90 percent of red light and transmits most green and blue light. If 100 units of red light strike the filter, about how many units of red light pass through?
- 3 Explain why mixing red, green, and blue light can make white on a screen, but mixing red, green, and blue paint usually does not make white.