the visible spectrum as part of the electromagnetic spectrum
(Credit: Abrisa Glass & Coatings, 2005)
X-rays, light, and radio waves are examples of electromagnetic waves.
Light is what we call the part of the electromagnetic spectrum that we can detect with our eyes. The cone photoreceptors in our eyes have evolved so that they are most sensitive at different regions of the visible spectrum. This forms the basis for our sensation of color
At the blue end of the visible spectrum, the wavelength of light is shorter — about 400 nanometers.
A nanometer is 1 billionth of a meter, or 1 × 10−9 meter. The abbreviation for nanometer is ‘nm’.
At the red end of the spectrum, the wavelength of light is longer — about 700 nm.
Cone photoreceptors have evolved into three different types. Each one is most sensitive to a different region of the visible spectrum. One type responds best to shorter wavelengths; another responds best to wavelengths towards the middle of the spectrum; and the third type responds best to longer wavelengths.
The different cone photoreceptors are not sharply tuned to a particular color, however. So a short-wavelength cone photoreceptor can still respond to longer-wavelength light that falls on it. It is more likely to respond to shorter wavelength light, but it is still possible for it to respond to mid- and long-wavelength light.
The signals from the three different types of cones are combined in the retina and in the brain, eventually giving rise to the sensation of color.
[ via Mixing Light ]