Lasers are fabulous tools that clearly show many key properties of light from basic optics to interference and quantum erasers . However, the safety of laser pointers is in need of clarification. Lasers of Classes I and II have beam powers of less than 1 mW and are generally considered safe for supervised classroom use. Lasers that are Class III or IV are considered to pose unacceptable potential danger. Now, check the labels on your laser pointers. You will find that they are all Class IIIA – even the cheap dollar store versions!
This is because there is a problem with the classification system. Class IIIA lasers are restricted to 5 mW while Class IIIB can put out up to 500 mW. That’s two orders of magnitude greater! So, should we be concerned about using these lasers? Dennis M. Robertson, an opthamologist at the Mayo clinic, has done some very clear studies on laser pointers and eye safety. In 2000 he pointed a 5 mW laser pointer at a human eye for 15 minutes (it was due to be removed for medical reasons) and he couldn’t find any effect. In 2005 he repeated the experiment with a green laser pointer. In this case, after 60 seconds, the patient reported no change in vision, but Dr. Robertson was able to detect changes to the retina. This makes lots of sense. Your retina is red, which means it absorbs green and reflects red. If it absorbs the light, it heats up. This is something that the classification system doesn’t address. I found a website selling a Class II green laser pointer. It stated “This pointer is visually the brightest laser one can find with a CDRH Class II rating … the highest class rating that many school systems permit.” You can find the articles at the website of the Archives of Opthamology, http://archopht.ama-assn.org/ . The articles are from Dec. 2000; 118: 1686-1691 and 2005; 123: 629-633.
So, it appears that the red laser pointers are safe to use in the classroom and the green laser pointers are questionable. It is really easy for students to purchase a dangerous laser over the Internet, so when we use a laser pointer we should take the opportunity to point out the real hazards of other lasers and model clearly how to use a laser so that the beam is never pointed or reflected near anyone’s eyes.