Optical safety of comparative theater projectors.

Abstract

Traditional movie projectors employing carbon arcs were introduced to movie theaters more than a century ago, and they were replaced during the 1950s by xenon-arc projectors. Today, these arc-lamp film projectors are expected to be replaced by digital laser projectors. Questions have arisen with regard to safety of the new laser-based projectors and about the comparable safety to the xenon-arc projectors that they replace. Smaller projectors employing tungsten-halogen lamps have been used for decades in home and office environments, and small arc-discharge lamps more recently have enjoyed widespread use in digital projectors. The trend in digital projectors has led to increased luminance projection products. Results of a comparative evaluation of ocular hazards from various projection systems, with an emphasis on professional laser illuminated projection systems, are presented. Irradiance and source size measurements were made to determine the radiance of each of the projection systems for both thermal and blue light hazards to the retina. Ultraviolet and infrared measurements were also made for completeness of the hazard evaluation. Projectors are classified by risk groups according to national and international standards, and recommendations for projector safety are provided. It is shown that laser illuminated projectors have hazard distances comparable to traditional 35 mm movie-theater projectors of the order of 1 m. Since there is no resemblance to the optical hazards of distant, collimated laser beams in light shows and only minimal hazards are posed by theater projectors to the audience, the standards and regulations applicable to "laser light shows" should not be applicable for these types of products.