These fixtures were popular for lighting bridges and dangerous intersections on account of their intrinsic bright yellow illumination without scattering light in fog and provided low glare to automobile drivers. Introduced around 1935 by General Electric, these lights required special equipment to operate them (their gear was enclosed in a compartment in the rear of their boxy fixture as seen). Typically, these luminaires employed NA-9 sodium vapor bulbs rated at 180 watts that provided 10,000 lumens. These were the most energy-efficient light sources in the lighting industry well into the 1950s when superceded by mercury vapor lamp technology..