MPE is short for Maximum Permissible Exposure. The MPE is the level of laser radiation, that, under normal circumstances, persons may be exposed without suffering damage.
In general the MPE is laser class 2, meaning max. 1mW. In some cases class 3R, meaning 5mW. Physically the standable exposure for human eye is very much above, but legal situation defines the MPE as shown above (IEC 60825-1)
It is no problem to make a safe beam show with a class 4 laser, because the laser class of the projector is in no direct relation with the MPE!
The laser class of the projector is the Accessible radiation (AR). It is the maximum possible emission that may exit the laser aperture. Limit values are given in IEC 60825-1 „Safety of laser products, part 1".
The MPE in contrast to the AR references the laser immission in public area - wich is completely different!
Many factors influence the MPE , like distance, scan speed, patterns scanned, etc. so every laser show situation needs to be evaluated individually!
Following video explains the differences between AR and MPE:
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