The human eye is extremely sensitive to the wavelength of green lasers—which is why they appear much brighter than red or blue beams. That’s not exactly why they’re dangerous—thankfully, because the human eye is so susceptible to green lasers, our blink reflex will naturally kick in, quickly shielding the eye from potential damage. And here’s where the cheapness factor comes into play: NIST found that standard laser pointers rated at 10 milliwatts can appear to be outputting substantially less than 10mw of green light. Instead, due to missing infrared-blocking filters, the lasers can be emitting substantial infrared radiation invisible—but harmful—to the human eye.
- green laser pointer to test(duh)
- piece of white paper
- black tape
- two paper cups (or anything to mount the laser and CD on)
To test the presence of too much infrared light:
- Cover the bottom of the CD with tape until only a small portion left uncovered to reflect light from the laser.
- Cut slits in the tops of each cup and nestle the laser into one and the CD into another; you want the laser resting flat, while the CD should be standing vertically. Align the laser pointer with the bare patch on the CD.
- Cut a small hole in the piece of paper and fit it over end of the laser pointer. Use some tape to hold the power button of the pointer down. At this point, your laser should be reflecting off the CD and onto the piece of paper!
- If your web cam supports night vision, point it at the back side of the paper. Voila! You’ll be detecting any stray infrared light.
- If your webcam doesn’t support night vision, read the appendix in the NIST report or find an online guide to perform the required modifications.