The laser classification system, created in the early 1970s, was revised in 2007 and then approved by the FDA. The system is an important part of laser safety, it can display the laser danger level, and can sell and own USB laser Pointers. These levels range from low (level 1) to severe (level 4), depending on how much damage the Laser Pointer can cause to the body. The possibility of laser damage is mainly related to the milliwatt output and the wavelength and exposure time. Level 2 lasers are safe as long as your eyes are in contact with the laser for less than 0.25 seconds. Usually, as a natural defense, the eyes blink before the 0.25 second limit. However, as a safety precaution, level 2 lasers should include a warning label that says something along the line "Don't stare at the beam." Like Class 1, Class 2 has a subclass called Class 2M, which marks the 0.25 second limit for laser safety, except through a magnifying glass.
The apparent brightness of the illuminated spot depends largely on the wavelength of the emitted light. Most devices operate in the region of the red spectrum, where the eye's sensitivity decreases rapidly with increasing wavelengths. The device with 650 nm output was about twice as bright as the device with 670 nm output, while the device with 635 nm output was still about twice as bright. However, laser Pointers with shorter wavelengths are usually more expensive. This is especially true for green lasers.