Eye safety for scanning laser projection systems

Abstract

In the growing field of pico-projectors, laser-based scanning systems may be advantageous over DLP- or LCoS-based imagers due to their potential for miniaturization, enhanced optical efficiency and cost reduction. The high energy density of a combined laser beam can, however, be hazardous to the human eye. Laser projection systems must therefore be identified with the laser class, depending on their maximum optical output power. This power limits the brightness of the displayed image, which is of particular interest for mobile applications. Various approaches to classifying laser devices by their wavelength and output power are described within the standards for laser safety. It is found that actual safety regulations cannot be directly applied to scanning systems. A detailed analysis of the optical conditions in terms of a two-dimensional extended light source is appropriate for the consideration of laser scanner devices. In this article, alternative ways of applying laser standards for scanning systems are discussed. The dependencies of maximum luminous flux from scanning system parameters are reviewed. It is shown that the evaluation of retinal light exposure in terms of existing laser regulations leads to an overestimation of the hazardous potential. Advanced investigations are proposed to support the definition of suitable criteria for the classification of laser scanning projectors.