Class I and II "Caution"

The lasers under Class I and II have a laser power of output less than 1mW. It is usually considered "safe" to human eyes. That means human eyes exposed to the laser radiation would not cause permanent retina damage of eyes. It is also suggested that people do not look into the laser beam a long time or view the beam directly with optical instruments.

Class IIIa "Danger"

Under this class, the output power of visible lasers is located in 1 - 5mW. It is generally thought that the beam will be unsafe to human eyes. To expose eyes to the laser radiation would result in a permanent retina damages. It is prohibited that eye or skin exposure direct to the laser beam.

Class IIIb "Danger"

The output power is between 5 - 500mW. The ones of invisible lasers are higher than 500mW. The eye retina will be heavily injured when exposed to the laser radiation under this class. It is prohibited that people stare into the beam including the reflected and scattered beam from high reflecting surfaces.

Class IV "Danger"

Class IV covers the visible and invisible lasers or laser systems whose output power is higher than 500mW. The powerful radiation including the reflected and scattered radiation can permanently cause human skin and eye retina damages. It is important that to avoid eye or skin exposure to direct or scattered radiation. The Class IV lasers should be used strictly under the professional control.