September 25, 2015 Filed in: Articles
Roberta Tevlin, OAPT Newsletter Editor, Physics Teacher Danforth CTI
The Standard Red Laser Pointers are Class IIIA and they are SAFE
There is a lot of confusion about which lasers we can and should use in our classrooms. Lasers are classified by power, spread of beam and a variety of other properties. The lower the Class, the safer they are. The incredibly useful and affordable red laser pointers that are commonly available are safe to use. They are Class IIIA lasers and are limited to 5 mW. You can’t hurt your eyes with them even if you try to! A test of this was written up in JAMA Ophthalmology
fifteen years ago. STAO’s older safety guidelines
say that “Only Class I lasers should be used in Science classes*.” These Class I lasers are the ones that are contained in foot-long boxes and cost hundreds of dollars! Important Update!
STAO changed their laser recommendation in their Safe ON Science publication (available for $12.60 for their online store
). It states that “Only Class 1 and 2 lasers are recommended for use in schools.”
In response to information that I have supplied to the STAO Safety Committee, they will be reviewing their recommendation as to Class 3A lasers. This committee has also provided new information from the NRC publication "Prudent Practices in the Laboratory" that indicates that:Class I (1) ... lasers are either completely enclosed or have such a low output of power that even a direct beam in the eye could not cause damage. Class II (2) lasers, can be a hazard if a person stares into the beam and resists the natural reaction to blink or turn away. Class IIIA (1M, 2M, or 3R, depending on ... output) lasers can present an eye hazard if a person stares into the beam and resists the natural reaction to blink or turn away or views the beam with focusing instruments.
After their review, they will contact OAPT with their results.
Class II Laser Pointers are now available!
I may have found a solution to this conflict. Class II laser pointers are now available. Perhaps STAO would consider this a reasonable compromise. I bought Quartet Slimline Laser Pointers at Staples for $18.94 each. These are Class II and less than 1 mW. Unfortunately they are not available online.
However, I also found a similar one for $20
and a green one for $35
at LASER Classroom. Sargent Welch
also sells these green lasers, but for $89.90!
Green Class III Laser Pointers are great for star gazing and will not blind pilots!
Jason Harlow (Associate Professor at U of Toronto) has a very nice post on his blog
where he takes you through his measurements and calculations to demonstrate to the campus police that he is not endangering anyone when he uses his laser pointer at star parties.
The exercise he goes through would be a great classroom activity for high school students in physics, grade 10 optics or math. They need to measure distance and spot size and then calculate the spot size for the typical distances of planes and helicopters. You could motivate the lesson with the Toronto Star article that he references, which says “The culprit is typically a green laser, which are often used by amateur astronomers to point out stars and constellations in the night sky. But in recent years, pilots have complained that pranksters are tagging their aircraft and trying to beam the lasers into their cockpits.” What a sloppy piece of journalism! It implies that the 5 mW lasers being used by teachers like Jason are equivalent to the 500 mW lasers being used by idiotic pranksters. Argghg!!
Laser Pointers can be very dangerous
I was horrified to find that it is much easier to buy dangerous laser pointers on the internet than the safe ones. The powerful ones are Class IIIB and they are a hundred times more powerful than Class IIIA. These can cause permanent eye damage at close distances. These can cause a serious accident if they distract a car driver or the pilot of a low-flying helicopter or plane. We should point out these real dangers to our students — but they won’t take us seriously if we try to claim that the standard red laser pointers are dangerous to your eye sight.