Why are lasers red?

Lasers are mostly red in color because red has the longest wavelength, approximately 650 nanometers. Because of this, red does not scatter easily and can be viewed from a long distance.

Apart from not scattering easily, the other reason why the color red is widely used in lasers is because it comes from helium and neon, which are the cheapest and most-reliable sources available. According to Michael Dubson, a senior instructor in physics at the University of Colorado, Boulder, "It is possible to make a laser in any color, but it would be expensive and pointless," and, therefore, red lasers are the most common.