This class is eye-safe under all operating conditions.
This class is safe for viewing directly with the naked eye, but may be hazardous to view with the aid of optical instruments. In general, the use of magnifying glasses increases the hazard from a widely-diverging beam (eg LEDs and bare laser diodes), and binoculars or telescopes increase the hazard from a wide, collimated beam (such as those used in open-beam telecommunications systems).
Radiation in classes 1 and 1M can be visible, invisible or both.
These are visible lasers. This class is safe for accidental viewing under all operating conditions. However, it may not be safe for a person who deliberately stares into the laser beam for longer than 0.25 s, by overcoming their natural aversion response to the very bright light.
These are visible lasers. This class is safe for accidental viewing with the naked eye, as long as the natural aversion response is not overcome as with Class 2, but may be hazardous (even for accidental viewing) when viewed with the aid of optical instruments, as with class 1M.
Radiation in classes 2 and 2M is visible, but can also contain an invisible element, subject to certain conditions.
Classes 1M and 2M broadly replace the old class 3A under IEC and EN classification. Prior to the 2001 amendment there were also lasers which were Class 3B but were eye-safe when viewed without optical instruments. These lasers are Class 1M or 2M under the current Classification system.
Radiation in this class is considered low risk, but potentially hazardous. The class limit for 3R is 5x the applicable class limit for Class 1 (for invisible radiation) or class 2 (for visible radiation). Hence continuous wave (CW) visible lasers emitting between 1 and 5 mW are normally Class 3R.
Visible class 3R is similar to class IIIA in the US regulations.
Radiation in this class is very likely to be dangerous. For a continuous wave laser the maximum output into the eye must not exceed 500mW. The radiation can be a hazard to the eye or skin. However, viewing of the diffuse reflection is safe.
This is the highest class of laser radiation. Radiation in this class is very dangerous, and viewing of the diffuse reflection may be dangerous. Class 4 laser beams are capable of setting fire to materials onto which they are projected.
Any laser product of a given Class may contain 'embedded' lasers which are greater than the Class assigned to the product, but in these cases engineering controls (protective housings and interlocks) ensure that human access to radiation in excess of product Class is not possible. Notable examples of this are CD and DVD players which are Class 1 laser products while containing Class 3R or Class 3B lasers and laser printers which are Class 1 laser products but contain Class 4 embedded lasers.
Note:- for a product to be classified correctly, it must be tested at the maximum output accessible under reasonably foreseeable single-fault conditions (eg in the drive circuitry). A non-M class product must pass both Condition 1 and Condition 2 of Table 10 in IEC/EN 60825-1, and an M-class product (which by definition has failed either Condition 1 or 2) must pass the irradiance condition in the same table.
* Generally speaking lasers are point sources while LEDs are extended sources. Extended sources have higher power limits than point sources for a given laser Class. Therefore a visible LED emitting 10 mW may be Class 2, while a visible laser pointer of the same power would be Class 3B. NB Laser pointers above Class 2 are banned for sale to the public by trading standards.