Philips Capillary Water Cooled Mercury SP500
The first water-cooled super high pressure mercury lamp was a 500W source created in 1935 by C. Bol of Stamford University. Lamps having extremely high brightnesses could then be created, typically in the region of 30,000 candles per square centimetre. Experimental types were even created having brightnesses as high as 180,000 cd/cm², equal to that of the sun - although the life was only a few minutes under such phenomenal loading! In all lamps the brightness depreciates very rapidly owing to devitrification of the quartz which scatters light and broadens the source size.

This fairly recent model follows the same design principles as the early lamps, but incorporates an integral reflector. The arc tube is 6mm diameter with 2mm wall thickness and has a tungsten wire electrode sealed into each end, separated by 12.5mm. A special graded seal using only one intermediate glass is employed. Special conical end chambers surround the electrodes, and these are almost completely filled with mercury. The electrode tips protrude approx. 0.5mm ahead of the reservoirs, and during operation the discharge is saturated, i.e. only part of the mercury evaporates. The reservoirs are necessary to prevent the seals from overheating and potentially cracking.

The reflector is of solid stainless steel and its surface profile creates four images of the arc beside the centre real image, forming an essentially square source area of extremely high brightness. The lamp is intended for operation inside a special water jacket of all-metal construction, apart from a small circular window housing a condenser lens in front of the arc tube. Production continued until the late 1970's when water cooled mercury lamps were made obsolete.
Manufacturer: Philips Lighting
Lamp Power: 500 Watts
Lamp Current: 1.35 Amps
Lamp Voltage: 450 Volts
Cap: Special
Bulb Finish: Clear Quartz Window
Bulb Type: T-19
Overall Length: 120 mm
Light Centre Length:
Electrodes: Solid Tungsten Wires (12.5mm arc gap)
Atmosphere: Argon
Luminous Flux: 30,000 lm (15,000 lm in projected beam)
Luminous Efficacy: 60 lm/W
Max Brightness, cd/cm2 30,000 (0 hrs) 22,500 (25 hrs) 15,000 (50 hrs)
Initial H.C.P.: 3,500 candle power
Rated Life: 50 hours
Factory: Eindhoven Netherlands
Date of Manufacture: February 1961
Original / Present Value: Not Known