Incoherent light sources, standards, and time-weighting

Abstract

Many LSOs are asked about potential hazards and safe use of non-laser optical sources such as arc lamps, ultraviolet lamps and light-emitting diodes (LEDs). Most of these sources do not pose a risk of thermal retinal injury, but may pose a risk of skin or eye injury from ultraviolet or visible radiation emissions. Since these are photochemical hazards, the actual total exposure - whether brief or protracted over a day - determines the risk. The risk assessment may show that a person could reasonably be expected to be exposed at only 20 cm for a minute, but at a distance of 2 meters for two hours. No one would be reasonably exposed over an entire work day. Then the LSO must estimate the worst-case, but reasonably foreseeable time-weighted-average (TWA) exposure in any one day. This concept is familiar to industrial hygienists who must determine TWA exposures to airborne contaminants, but is not generally encountered during laser safety assessments, since most laser risks of concern are from momentary accidental exposures. Some general guidelines are provided for exposure assessment for lamp sources and the currently available photobiological safety standards for lamps and lamp systems will be addressed. There are four risk groups applied in the lamp safety standards.Many LSOs are asked about potential hazards and safe use of non-laser optical sources such as arc lamps, ultraviolet lamps and light-emitting diodes (LEDs). Most of these sources do not pose a risk of thermal retinal injury, but may pose a risk of skin or eye injury from ultraviolet or visible radiation emissions. Since these are photochemical hazards, the actual total exposure - whether brief or protracted over a day - determines the risk. The risk assessment may show that a person could reasonably be expected to be exposed at only 20 cm for a minute, but at a distance of 2 meters for two hours. No one would be reasonably exposed over an entire work day. Then the LSO must estimate the worst-case, but reasonably foreseeable time-weighted-average (TWA) exposure in any one day. This concept is familiar to industrial hygienists who must determine TWA exposures to airborne contaminants, but is not generally encountered during laser safety assessments, since most laser risks of concern are from momentary accid...