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What are the quantifiable criteria that are used to assign a safety classification to a laser? Googling finds me only vague subjective descriptions, like "safe to use under normal conditions" or "capable of harm". Presumably, whoever assigns these labels isn't simply shining them into someone's eyes to see if it "does harm".

I see lasers for sale online that often don't advertise their classification, but give all other details about the laser. For example, if one was advertised as 0.25mW output at 800nm wavelength with a 75% duty cycle, how would I estimate it's safety classification?

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  • $\begingroup$ A web search on ANSI Z136 will bring up many links to the Laser safety standards. Do you really have a link to an 800 micron laser? 800nm would put it outside of the 'visible' to ANSI, i.e. the blink reflex really won't help you. Skimming the limits, it is likely 3a (but I am not a laser safety officer, so talk to your local expert). $\endgroup$ – Jon Custer Sep 8 '15 at 16:36
  • $\begingroup$ In general it is not a good idea to shine ANY laser light into ANY eyes. The safety classification is a legal tool that your attorney will rely on when you are being sued for damages, it's not something that you should use as an engineering guideline to design a laser show. If you happen to work with an unclassified product (i.e. pretty much everything from China that you can buy on the internet), then there is probably little that will save your purse in case of a lawsuit. But then, IANAL, just a very careful physicist. Ask your lawyer for details. $\endgroup$ – CuriousOne Sep 8 '15 at 20:15
  • $\begingroup$ @JonCuster, You can find tons of them on Ebay or Amazon. Here's one. $\endgroup$ – Cerin Sep 9 '15 at 0:59
  • $\begingroup$ Yup, and that is an 800 nanometer (not micron!) wavelength... Bare laser diodes in this wavelength were available 30 years ago (and I recall using them to great effect for experiments). As a barely-visible line (most folks eyeballs are rolling off quickly - get similar-power 830 and 860 nm lasers and you will see how quickly they get dim) you need to be extra careful, but 3a probably covers it. $\endgroup$ – Jon Custer Sep 9 '15 at 13:31
  • $\begingroup$ @Jon Custer, you're right, I've edited my question. Thanks. $\endgroup$ – Cerin Sep 9 '15 at 23:32
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There are five classes of laser:I, II, IIIa, IIIb, IV. These are decided based on the power output of the laser, whether it is visible light, and whether it is safely enclosed with interlocks.

Since your laser is a low power, unenclosed, infrared laser it is probably a class IIIa. If the same laser were inside a commercial CD player it would be rated class I, because there is no danger of accidental exposure to laser radiation.

Wikipedia contains an excellent summary: https://en.wikipedia.org/wiki/Laser_safety#Classification

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