Hello Laser Gurus,

I'm seeking some safety expertise...

I'm in the process of creating a temporary public art installation that will feature about 750 class II <1mW laser diodes. The beams are being defocused using convex acrylic lenses and/or pieces of textured glass, but I want to be 110% percent sure that there is no potential for anyone to harm themselves when interacting with the art.

I know class II lasers are generally safe because of the blink reflex, but in this application, the laser beams will be diffused to create moving patterns/pools of light several inches in diameter. While I'm sure this greatly reduces the amount of radiation entering the eye, I want to make sure that if someone were to intentionally stare at the beams for an extended period of time, there would still be no potential for eye injury.

So that I don't have to use my retinas/corneas as Guinea pigs, is there a formula I can use to calculate the maximum permissible exposure time given the laser wattage and the beam's diameter at the point it enters the eye?

Thanks for your help.
East

A class II laser is considered completely safe, even if you don't blink while staring at it. Making the beam thicker than 7mm (which is about the maximum pupil diameter) will make it even safer. You have nothing to worry about.

Class I is completely safe, like a barcode scanner. Class II is safe with a normal blink reflex and goes up to 1mW. This is for a collimated beam that can completely enter the eye.

Look the MPE (maximum permissible exposure) up on wikipedia. For 400-700nm, 0.001W/cm^2 = 1mW/cm^2 is completely safe for very long term exposure (at least 1000 second, the graph stops there). If nobody can reach the laser beam before it has expanded beyond 1 cm^2 for a 1mW laser, it will be safe. A 1mW beam with a few inches in diameter will thus be perfectly safe.