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This is photo number 375-954A, dated September 1, 1967.  It was taken through a view port in the lamp basement (or solar basement) of the 25-ft Space Simulator in building 150, shortly after the simulator had been upgraded and testing was completed.  This is an array of 37 –  20kw Xenon arc lamps, each inside a reflective collector and having its own gimbal so they could be individually aimed at a lens.    Behind the lamps is the air cooled stainless steel radiation shield that surrounded them.  Under the lamps are a water cooling system, electrical wiring, and other hardware.  The diagram below is from Design and Construction of the 15-ft-Beam Solar Simulator SS15B, October 1, 1968, JPL TR 32-1274.  You can see the full report on the NASA Technical Reports Server.  https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690008610_1969008610.pdf

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