Assessing irregular extended sources

The aperture averaging of an extended-source radiance distribution depends upon exposure duration and whether the potential injury mechanism is thermal or photochemical. A standardized method has evolved over the past four decades for dealing with this. However, with the 2014 revisions of the ANSI Z136.1 and IEC 60825-1 standards, the approach can be simplified for short pulse durations because of the revision of the exposure limits that describe a constant radiance above 5 mrad for pulses less than 0.625 ms. Regardless of the irregularities of a pulsed source, the localized retinal irradiance determines the potential for retinal injury. Hence only a 1.5-mrad and a 5-mrad averaging field-of- view is necessary when hot spots are smaller than 5- mrad; whereas, only a 5-mrad field-of-view is required for sources with hotspots that are greater than 5 mrad. Because of radial heat-flow away from any localized areas of high retinal irradiance (i.e., high source radiance) and because of eye- movements, larger averaging areas may be employed for lengthy exposures. A standard 11-mrad field-of- view is employed to account for eye movements when exposures are of the order of 10-100 s. Repetitive-pulse exposures and exposures greater than 0.625 ms may require consideration of more than one aperture to properly account for heat-flow and eye movements.