Low pressure sodium as a light source was cutting edge in its day owing to their remarkable energy efficiency and much longer life than conventional filament lightbulbs. The appearance of the this illuminant was a distinct yellow-orange color which made their applications restricted to outdoor lighting, particularly for illuminating highways and streets. Commencing in the late 1940s mercury vapor lamps became the outdoor lighting source of choice due to their compact size, somewhat improved color rendition and smaller fixtures. Low pressure sodium lighting provided excellent visibility for cutting through fog without scattering the light. This light source and their special fixtures, very similar to those you see here, were used on the Golden Gate and nearby SF area bridges through the late 1960s.