Bulb testing. Researchers test the heat output from a high intensity discharge light bulb. This type of bulb creates light from a plasma discharge rather than the filament of conventional light bulbs. The bulb is more energy efficient than halogen lighting, while producing three times more light. Gas within the glass bulb is ionised by two electrodes which causes a plasma discharge, and light to appear. Photographed at Osram Sylvania, Beverly, Massachusetts, USA in 2005.