Diode laser emission dangerous to eye - Why? Why is a solid state laser diode pen which emits eletromagnetic radiation in the form of a constant range of undulating photons harmful to the retina? In other words, (Did I use the technical terms right? "Undulated" means 'wavelength' correct?)why is diode laser radiation(for example from a laser pen) harmful to the eye? Since the eye has a hole in it (the black part of your eye.), this hole is vulerable to the high intensity of a laser beam and cannot adjust accordingly. For example, in a dark room, wouldn't looking directly into a laser beam (common laser pen) more dangerous than in a room illuminated with light? Since in dark light your pupil is dilated more, therefore it's even harder for your eye to comphensate to the laser. Since photons have no mass, what exactly happens when a stream of photons goes though your pupil, into your retina? Why is this so damaging? Thank you.