Class 1: A Class 1 laser is considered safe based upon current medical knowledge. This class includes all lasers or laser systems which cannot emit levels of optical radiation above the exposure limits for the eye under any conditions inherent in the design of the laser product. There may be a more hazardous laser embedded in the enclosure of a Class 1 product, but no harmful radiation can escape the enclosure.

Class 2: A Class 2 laser or laser system must emit a visible laser beam. Class 2 laser light is too dazzling to stare into for extended periods. Momentary viewing is not considered hazardous since the upper radiant power limit on this type of device is less than the Maximum Permissible Exposure for momentary exposure of 0.25 seconds or less. Intention extended viewing, however, is considered hazardous.

Class 3: A Class 3 laser or laser system can emit any wavelength, but it cannot produce a diffuse (not mirror-like) reflection hazard unless focused or viewed for extended periods at close range. It is also not considered a fire hazard or serious skin hazard. Any continuous wave (CW) laser that is not Class 1 or Class 2 is a Class 3 device if its output power is 0.5 W or less. Since the output beam of such a laser is definitely hazardous for intra-beam viewing, control measures center on eliminating this possibility.

Class 4: A Class 4 laser or laser system is any that exceed the output limits (Accessible Emissions Limits, AELs) of a Class 3 device. As would be expected, these laser may be either a fire or skin hazard or a diffuse reflection hazard. Very stringent control measures are required for a Class 4 laser or laser system. Ultrafast lasers fall into this classification.