RLOD#14 (2020.05.20) 1970s Philips GL92

Philips introduced its GL9X series of high-brightness negative glow discharge lamps in 1967 with the orange neon-filled GL90, followed in 1968 by a green fluorescent neon-xenon-filled GL91 model. These lamps are characterized by a unique double-ended design which was invented at Philips in 1965 in order to maximize brightness in the smallest volume possible. The electrodes consist of wide bands of soft iron, placed side by side with a very small gap in between, and located off axis in the lamp. Such configuration presents several advantages over that of standard single-ended glow lamps, such as a minimized dead space (small Faraday dark space), no shadowing, and a directed light emission. Moreover, the large electrode surface area enables a high drive current of 3.5 mA, resulting in a power dissipation of nearly half a watt, the highest of all glow indicator lamps made by Philips in the early 1970s. From all those elements result a very compact source with a high power-to-length ratio of ~0.15 W/cm.

The GL92 shown here is a very rare and never-listed blacklight variant made with a Wood’s glass bulb internally coated with lead-activated barium silicate phosphor, and filled with a neon-xenon gas mixture. This source radiates in the UV-A around 351 nm and was intended for fluorescence applications such as instrument panel illumination, especially in aviation. Although groundbreaking in its design and characteristics, this particular glow lamp technology did not prove particularly popular on the market and Philips eventually phased it out in 1980.