Lasers can be classified into four broad categories according to the physiological harm they may cause. Each laser device should have one of the following four marks.
Class I: This laser does not cause any known degree of damage.
Class I.A.: This is a special class for lasers "not suitable for direct viewing with the eye," such as laser scanners used in supermarkets, which have a maximum power limit of 4.0 milliwatts.
Class II: Refers to a low-power visible light laser with an emission power higher than class I, but with a radiation power of not more than 1 milliwatt. Man's automatic defensive response to bright light can protect him from harm.
Class IIIA: refers to the medium and low power laser (continuous wave: 1-5MW), which will pose A danger only if the beam is seen internally. Most pen-shaped laser Pointers fall into this class.
Class IIIB: Lasers of ordinary power.
Class IV: refers to a high-power laser (continuous wave: 500 milliwatts, pulse wave: 10J/CM2 or diffuse reflection limit), in any case, whether directly or indirectly observed, is dangerous and may cause fire or skin burns. Class IV laser equipment must be subject to strict control.