1973 Philips 7389 (500 W / 240 V)

Introduced in the early 1970s, the Philips model 7389 is a 500 W tungsten-halogen lamp designed to replace sealed-beam lamps in PAR can luminaires (with the addition of a parabolic mirror). To that end the lamp has a very compact construction featuring a GY9.5 base and a precisely aligned monoplane filament. The quartz bulb is filled with argon, nitrogen, and dibromomethane, a recipe which was developed at Philips during the second half of the 1960s and which enabled lamps of the present kind. The tungsten filament is operated at a very high temperature so as to realize a high source brightness and output. The latter is 45 % greater (14.5 vs. 10.0 klm) than that of standard half-kilowatt stage halogen lamps, resulting in an high lumen efficacy of 29 lm/W. The drawback, however, is a service life limited to 50 h only, which is sufficient for the intended application of effect lighting in studio, theatre, and disco settings. Philips released three lamps rated from 500 to 800 W for that particular application, with the present 7389 model being the most efficient.