Optical systems emitting radiation in the visible and near infrared wavelength range represent a potential hazard for the retina of the human eye. This can result in irreparable damages due to photochemical, photothermal, photomechanical or thermomechanical interactions. To perform an eye safety evaluation a distinction must be made between coherent light sources and broadband light sources. For both types of light sources the corresponding safety standards, namely the IEC 60825-1:2014 and the IEC 62471:2006, provide accessible emission limits which depend on the angular subtense of the apparent source. This parameter is not a characteristic of the light source but must be determined by the irradiance distribution of the retinal image in case of coherent radiation and by the spectral radiance distribution of the retinal image in case of broadband radiation. This investigation introduces software-based methods investigating the retinal image in order to calculate the angular subtense of the apparent source. The results can be used to perform an eye safety evaluation in conformity with the laser safety standard IEC 60825-1:2014 as well as with the lamp safety standard IEC 62471:2006. However, the procedures given by the standards are not clearly defined. For this reason different implementations are discussed and compared to each other for a broad variety of exemplary retinal images.
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