TSD-2000-5-1 OPTICAL POWER: SAFETY LEVELS Issue 4
This document addresses the latest developments in the definition of Classes of the LED and LASER devices that are used in optical transmission systems. These definitions have been amended in 2001, so this document provides information that is as up-to-date as possible. The document also explains why the different Classes are needed. It is not simply an issue of the optical power involved, although this is a key consideration. The nature of the issue is affected by the transparency of the cornea, which varies over the wavelength range in question. At some wavelengths the cornea is transparent, so the radiation will penetrate to the retina. This may be damaged it if the power levels are excessive. At others the cornea is opaque, so it will be here that the optical energy will be dissipated. Also, if the light is in the visible part of the spectrum, the eye may be protected by the ‘blink’ reaction. Methods of providing protection range from defining work areas, such that only trained individuals are permitted to access areas defined as hazardous, through the design of equipment such that dangerous light levels are not accessible (shutters, etc), to individual protection by the wearing of goggles.