These were used in the late 1950s to operate complete strings of streetlights connected in parallel (or multiple). From what I understand, these were the second generation of tube-powered photo controls - the first generation units were mounted on a bracket and used a bell jar-shaped cover. These socket-mounted units were typically located on the north side of the pole to best capture the uniform progression between dusk and dawn that actuated these controls. The vertical tube in the middle is the actual sensing element and the two black circles are the other two tubes - both of which were very commonly available radio types. As technology advanced, these quickly became obsolete in favor of smaller and simpler units that mounted on each individual streetlight. This particular unit was made by the Fisher-Pierce Co. of Massachusetts (and is still in business to this day - and they even offer a modern-day version of this exact control!).