Because of the eye’s limited range of accommodation, laser and lamp (e.g. LED) safety standards require evaluation of time-dependent maximum permissible retinal irradiance only for exposure distances where the eye is able to focus on the illumination source (i.e. when the source is at least 100 mm or 200 mm from the cornea per IEC 60825-1 and IEC 62471, respectively). However, for a growing number of illumination systems found in consumer electronics devices (e.g. eye tracking), the short distance between the source and the eye precludes the eye from focusing on the source and results in a larger illumination area on the retina. Despite the inability for the eye to focus on objects at this close range, there exist certain configurations of sources where the retinal hazard for the source at distances closer than 100 mm can potentially exceed the retinal hazard of the source at 100 mm.
We will use a mixture of analysis techniques, including analytic formulations and ray tracing, to study the retinal hazard for illumination sources close-in to the eye. We will also calculate the power-to-limit ratio (PLR) at different source distances to understand the distance dependence of retinal hazards. This analysis will also frame these retinal hazard levels in the context of international safety standards.