Corey Vesper, of Nayland College, asks :-

Does the red laser light used in decoders at supermarket checkouts emit radiation that causes sterility?

Rob Coppell, a physicist at the National Radiation Laboratory, Christchurch, responded.

No. The supermarket scanner emits only red light and does not affect human reproduction.

Visible light is electromagnetic radiation which can be seen by our eyes as compared to radiowaves, microwaves and x-rays which cannot. Red light can heat tissue but not enough to cause damage unless the beam is highly concentrated. Light can not penetrate much deeper than the skin so it cannot harm internal organs.

The main danger from common lasers is to our eyes. Lasers produce light waves which are restricted to a very narrow band of colours (frequencies) and to a very narrow beam so that the beam is focussed by the eye onto a very small spot on the retina, the light detecting surface at the back of our eyeball. If the power is sufficient then that tiny part of the retina will over-heat and die.

For safety reasons lasers are divided into classes. Class 1 means we can stare into the beam without damaging the retina. Class 2 means our blink reflex will normally protect the eye from damage. Class 3 covers lasers for which eye damage may occur before we have time to blink. Class 4 lasers are very hazardous and can damage skin as well.

Most scanners in supermarkets use Class 2 type lasers so that our blink reflex will protect our eyes. Nevertheless, don't stare into the beam on purpose.