The visible light spectrum is the region of the electromagnetic spectrum that human eyes see. It runs from wavelength of about 400 nanometers (nm) at the violet end of the spectrum to around 700 nm at the red end of the spectrum. Ultraviolet light and x-rays are the ionizing radiation beyond violet, while wavelength on the other side of red are infrared, microwaves, and radio waves.
Wavelengths and Colors of the Visible Spectrum
Isaac Newton coined the word spectrum in 1671 in his book Opticks. Spectrum is Latin for “appearance” or “apparition” and Newton used the term to describe the rainbow spectrum produced by sunlight passing through a prism. Sunlight is a form of white light, which is the color you get when all of the wavelengths of light blend together. Newton saw the colors red, orange, yellow, green, blue, and violet. But, he added the color indigo as a seventh color because he wanted to relate the colors to the seven days of the week, moons and planets known at the time, and notes of the musical scale. So, you may have learned the colors of the spectrum using the mnenonic device ROYGBIV, for red, orange, yellow, green, blue, indigo, and violet. Modern science has pretty much done away with indigo, since the human eye isn’t great at distinguishing it from either blue or violet. The modern range of wavelengths and colors distinguishes deep blue and light blue.
| Color | Wavelength | Frequency | Photon Energy |
| Red | 625-700 nm | 400-480 THz | 1.65-1.98 eV |
| Orange | 590-625 nm | 480-510 THz | 1.98-2.10 eV |
| Yellow | 565-590 nm | 510-530 THz | 2.10-2.19 eV |
| Green | 500-565 nm | 530-600 THz | 2.19-2.48 THz |
| Light Blue | 484-500 nm | 600-620 THz | 2.48-2.56 eV |
| Deep Blue | 450-484 nm | 620-670 THz | 2.56-2.75 eV |
| Violet | 380-450 nm | 670-790 THz | 2.75-3.26eV |
Real vs Theoretical Visible Spectrum
Although scientists assign wavelength ranges for the colors, they are continuous. There aren’t any boundaries between one color and another. The wavelength limits of human vision are ambiguous, too. Some people can see further into the infrared and ultraviolet than others. Usually, humans (and animals) that can see further into one end of the spectrum don’t see as far at the other end of the spectrum. For example, birds perceive ultraviolet light, but don’t see infrared. The human eye actually perceives ultraviolet light just fine, but the lens filters it out so the high energy light doesn’t damage the retina. Some people with artificial lenses report seeing ultraviolet.
RGB monitors aren’t able to reproduce the colors of the spectrum accurately. But, if you don’t have a prism handy, you can see the colors on a screen by rendering the spectrum against gray. You may see further than 400 nm or 700 nm, but most people see 425 nm to 690 nm.
Colors Beyond the Spectrum
The eyes and brain see many more colors than those of the visible light spectrum. For example, purple and magenta aren’t on the spectrum. They are the brain’s way of connecting red and purple. There are also desaturated and blended colors, such as pink and brown. Mixing pigments on a palette forms hues and tints that aren’t spectral colors.
References
- Agoston, George A. (1979). Color Theory and Its Application in Art and Design. Berlin: Springer. doi:10.1007/978-3-662-15801-2
- Bruno, Thomas J.; Svoronos, Paris D. N. (2005). CRC Handbook of Fundamental Spectroscopic Correlation Charts. CRC Press. ISBN 9781420037685.
- Evans, Ralph M. (1974). The Perception of Color. New York: Wiley-Interscience. ISBN 978-0-471-24785-2.
- McLaren, K. (March 2007). “Newton’s Indigo”. Color Research & Application. 10 (4): 225–229. doi:10.1002/col.5080100411