Ben Armitage, an optometrist in Hobart, Australia, was recently confronted with a 14-year-old patient who had shined a laser pointer directly into his eyes for only a brief period of time. Despite the brevity of the occurrence, the boy's vision was decreased by 75 percent. "The laser burns are basically areas where he's not going to be able to see ever again," said Armitage.
Sure, it's fun to make your pet chase laser beams, but beware: the more powerful the laser, the more damage it can do. Lasers can pop a balloon, light a match, cut through plastic, ignite steel wool, or even, as in the case above, cause immediate and permanent blindness.
The word laser is actually an acronym for Light Amplification by Stimulated Emission of Radiation. Ordinary light is made up of many different colors. Laser light is made up of just a single color. Because it's amplified, laser light is focused and extremely bright. And it comes in a variety of colors and powers.
Laser power is measured in milliwatts (mW), and those that put out less than 5 mW are generally considered safe. Our eyes have a built-in blink reflex that makes us close our eyes or turn our head away when we're exposed to a bright light. That reflex typically happens in a quarter of a second, which is fast enough to minimize any damage the light might do. But we can override that reflex by deliberately shining a laser directly into the eye. When that happens, the laser can burn a hole in the retina. Lasers that put out more than 5 mW of power are especially dangerous, because they can start burning the retina before the blink reflex kicks in.
Color plays an important role as well. Our eyes are naturally more sensitive to red light than to blue or violet, so while we might turn away from a 5 mW red laser, we might not turn away from the same power blue or violet one. Our eyes are even more sensitive to green light than to red, but green lasers also emit radiation that we can't see, which makes green lasers even more dangerous than red ones.
Unless you're using a laser for some kind of industrial purpose, there's no reason for you to have one that's any more powerful than 5 mW. In fact, the FDA has proposed a ban on handheld lasers (such as laser pointers) over that threshold. However, it's still extremely easy to get lasers 10 or 100 or more times more powerful on the internet (and no, we aren't going to tell you where).
So here's the bottom line: Lasers are not toys, even if they're rated at 5 mW or fewer. Never, ever shine one at anyone else or directly into your eye (that includes bouncing the light off of a mirror or shiny surface into your eye). And never allow a child to play with a laser. Theoretically, it should be easy to tell whether a laser's power is low enough that you can use it safely. Unfortunately, in one of the few examples of products over-delivering on the promises made on their label, the ratings on laser devices routinely underestimate their actual power. Often by a lot.
If a laser pointer runs on tiny, button batteries, it's probably okay. However, the pointer you're considering may be stronger than 5 mW if it runs on AA or AAA batteries, or if it claims to be "military grade," "powerful," or advertises a range of several miles.