Dot reflection dangers

[Raiden Gekkou]

I'd personally say that anything 100mW and up can quickly cause eye damage up close, just to be on the safer side.

 

[Joshuan]

Um, guys, that 500mW is no magic number, even if it is used to designate between Class 3b and Class 4 lasers. The meaningful distinction between a Class 3b and Class 4 laser designation is that the Class 4 is an environmental hazard (e.g. fire), whereas anything Class 3b and above is an eye hazard, but generally not going to burn things without trying hard.

That "trying hard" carries meaning too. You can produce power densities rivaling Class 4 lasers if you use a magnifying glass with Class 3b or possibly Class 3r lasers. Everyone knows that people can burn paper and matches by focusing a weaker laser down. That 500mW is just a ball-park power figure for a laser beam of an average diameter (3mm? I don't know). Likewise, if you spread out a Class 4 laser over a wide area, it may not actually be harmful for your eyes.

To summarize: don't think you're "safe" viewing a dot from a 30mW anymore than 500mW. The latter has greater potential to cause damage, but they're both not eye-safe in different conditions. You should also wear goggles for the incidents you don't plan for; that's what they're really there to protect you against. What if you bump the table and the laser reflects off the shiny surface of your desk or something? Even a reflection off a diffuse surface may hurt your eyes, or at least irritate them. You should enjoy viewing your lasers, not squint and look away because you're uncomfortable.

I understand what you're saying and I agree with you. Don't get me wrong I'm not defending the lack of goggles or irresponsible laser practice. But a thing is that the main reason why we use lasers is to have fun, and obviously we should do that in a responsible way, but if we're not burning or doing any focus work many times goggles can be avoided, especially if you're handling lasers in the 15-60mW range (above 100mW things start to get trickier). As long as you don't point it directly at someone's eyes or a mirror you should be safe. At this power even most small accidents (like a shiny metal surface in the street or a window inside your room) are unlikely to cause permanent damage to the retina.