Dear Straight Dope:
You know those pen size red laser pointers? They are really low power, I know, and don't hurt the eyes perceptibly, but can they cause damage to the eyes over time? How long would you have to shine it in someone's eyes to cause damage and what would that damage be? I heard somewhere about a guy who used one at a girls' hockey game to come on to the girls by shining it in there eyes while they played. Apparently he was charged with assault and battery, but maybe other reasons factored into the charge. Anyway, what's the story on the safety of laser pointers?
SDStaff Czarcasm replies:
According to my research, some laser pointers are safe — up to a point. Reassuring, isn’t it?
The majority of the laser pointers used in the U.S. are Class 3a diode lasers in the 630-680nm wavelength (translation: your garden-variety red laser), with a maximum output of between 1 and 5 milliwatts.
Here’s where it gets a little tricky. The FDA has determined that Class 3a lasers could cause injury to the eye if viewed directly for approximately 0.25 seconds. You’d think this would be enough to ban them, but the FDA cited evidence that exposure to visible lasers is “usually” limited by the blink reflex of the eye, which they have timed at just under 0.25 seconds. Quite a coincidence, I’d say. Be that as it may, the FDA has issued a warning that the pointers aren’t toys, shouldn’t be used by children except under adult supervision, etc.
Others have taken firmer action. The U.K. has banned the sale and use of all but low-powered laser pointers, and many school districts in the U.S. have banned them as well — here’s a news account of a kid who used one to hurt a teacher.
Damage can include, but is not limited to, flash blindness that can last for minutes, partial vision loss that can last for months, permanent damage to the retina, and loss of life if the police officer who you are pointing the laser at thinks that she/he is being targeted and decides to shoot you in self-defense. (I exaggerate only slightly — there have been reports of officers who drew their weapons after mistaking the laser light for a gun sight.)
Now, to add to this, I’ve got some good news and some bad news. First the good news: Most lasers manufactured before 1993 were Class 2 lasers with a power output of less than 1 milliwatt, which would make them somewhat safer than the ones put out today.
The bad news? More powerful laser pointers have recently been imported from Russia and China. These lasers emit a green beam, and have emissions significantly exceeding the maximum permissible exposure. One of these lasers was found to have a removable filter. When removed, this laser pointer had an output in excess of 15 milliwatts, which would make it a Class 3b laser. Not something I’d put in my son’s Christmas stocking.
The International Journal of Safety and Standards — http://www.us.tuev.com/news/ newslett/nl0199/item2.html (Link now defunct)
SDStaff Czarcasm, Straight Dope Science Advisory Board
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