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
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
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
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.