Laser light is both varied and unique. It can be a continuous or pulsed beam, its wavelength can range from infrared to ultraviolet, it can range from an output of millionths to quadrillions of watts. For each specific laser, every photon has exactly the same wavelength, step, and direction. The beam is monochromatic, coherent, and collimated, which means that the photons are traveling parallel to each other. This results in a beam that widens very slowly. A laser beam shone at the moon from the Earth's surface (384,467 km) will only spread to 1.6 km, which is an angle of less than 0.000238 degrees. The photons also wave in the same direction, which means the beam is polarized. One can take a laser pointer and polarized sunglasses and rotate the beam to vary it from full power to nearly invisible.

Lasers are grouped into four basic categories based on their harmfulness.
Class I – Cannot be harmful
Class IA – Not harmful, but not intended to be viewed under normal circumstances (e.g., checkout price scanner.)
Class II – Can be harmful to view, but normal reaction to bright light should protect eye
Class IIIA – Hazardous to view. Most laser pointers are IIIA
Class IIIB – Moderately powerful
Class IV – Very dangerous; even diffused beams can damage tissue