You may recently have read an article on the BBC website about the safe use of interactive whiteboards and similar data projectors. The concern is that the strong light of the projector beam could damage the user's eyesight. The NUT guidance on this matter can be summarised as follows.
• Never stare directly into the projector beam;
• Keep your back to the beam as much as possible, and avoid standing facing into the beam for more than a few seconds at a time (the use of a stick or laser pointer is helpful in this regard); and
• Always step outside the projector beam when turning to face the class for more than a few seconds.
It must be emphasised that it is not good enough to simply avoid looking directly at the projector lens. Standing with the lens in your peripheral vision for more than a few seconds may still cause damage. Research suggests that the maximum safe exposure is between 10 and 20 seconds.
A full copy of the NUT advice can be found at Guidelines For Users Of Data Projectors [updated link, 31 Mar 2008]