Applications of thin film reflecting coating technology to tungsten filament lamps

The development of multilayer dielectric coatings to provide a visible transmitting/infrared reflecting filter for use on incandescent lamps, particularly focusing on application to compact tungsten-halogen lamps, is reviewed. The potential benefits in lamp efficacy improvements obtained by converting some of the infrared into visible radiation has been known for some time. However, the system design constraints and, in particular, the film deposition process, has proved very difficult to surmount, and thus introduction of general lighting products utilising infrared reflecting filters has only recently occurred. The major focus of the report is a review of material requirements and development issues associated with the deposition processes suitable for manufacture of such filters.