Laser alignment using a diode or Helium Neon laser can involve looking for a prolonged period at a bright spot on a matt target screen. Such diffuse reflections from Class 2, 3A and 3B lasers are deemed safe for prolonged viewing*, but there have now been a number of cases where such viewing has resulted in temporary loss of visual response to red light.

'The alignment spot I was watching just disappeared, and for an hour afterwards I could not see the beam or indeed anything else that was red.'

These experiences of laser users are examples of a retinal saturation effect which is well known in it's more common and far less extreme form to those in the design industry who have the job of colour matching. The effect is strongest for red light.Laser alignment using a diode or Helium Neon laser can involve looking for a prolonged period at a bright spot on a matt target screen. Such diffuse reflections from Class 2, 3A and 3B lasers are deemed safe for prolonged viewing*, but there have now been a number of cases where such viewing has resulted in temporary loss of visual response to red light.

'The alignment spot I was watching just disappeared, and for an hour afterwards I could not see the beam or indeed anything else that was red.'

These experiences of laser users are examples of a retinal saturation effect which is well known in it's more common and far less extreme form to those in the design industry who have the job of colour matching. The effect is strongest for red light.

The safety angle is, of course, that the blink reflex will provide no protection against exposures to a red laser beam during the time a person is suffering from 'red saturation blindness'

* To be precise, EN 60825-1 states that diffuse reflections from a Class 3B laser are safe for viewing conditions of less than 10 seconds exposure duration and more than 100 mm viewing distance.