RLOD#26 (2020.06.01) 1948 Philips 6004S

The development of the coiled tungsten filament lamp operating in a gaseous atmosphere opened the way for high-brightness incandescent sources suitable for mainstream film projection applications. The first of such lamps was introduced in the second half of the 1910s and was made possible by very compact filament structures operating at high temperature. However, optical efficiency was limited by the large bulbs used at the time to limit the blackening rate and the risk of overheating. Philips solved these problems by using the stack effect to carry evaporated tungsten away from the filament and make it condense in a larger and cooler chamber near the end cap, which is placed upward. This, and the down-flow of cool gas, enabled a much smaller bulb diameter around the filament. Chimney-type incandescent lamps were introduced in the mid-1920s, and the model 6004S shown here is a variant featuring a silvered spherical side mirror. Philips opted for a 15 V filament operating at 49.5 A in order to maximize the source luminance, enhanced by the back reflection of light. This lamp was the brightest incandescent projection source sold by Philips at the time, one that could replace small carbon arcs in film projectors, with the benefit of a stable light output without the need for constant adjustments. Such lamps were eventually phased out in the early 1950s as Osram’s then-new xenon short-arc lamp replaced the carbon arc in movie projection applications while a variety of other incandescent lamps were introduced to cater to lower-lumen projectors intended for home movies and photographic slides.