Wavelength and Color

A property of light that we discussed in class was it's wavelength (the distance between peaks of a wave).
On the image at right, working from top to bottom, you can see that wavelengths range from 10^-15 meters (gamma rays) to 10⁵ meters (radio waves).
This picture of the electromagnetic spectrum shows several wavelength regions, for example X rays, visible light, and microwaves.
The light that our eyes are sensitive to lie in a very small region of the electromagnetic spectrum labeled visible light corresponding to a wavelength range of 400 - 700 nanometers and a color range of violet through red. So if someone says that a photon is "redder" than another, they mean it has a longer wavelength. Similarly, a "bluer" photon would have a shorter wavelength.

Wavelength and Energy

And, as mentioned in class and section, a shorter wavelength means more energy. So a blue photon carries more energy than red photon.