GE-Mazda Miniature Oval-Section Blue Fluorescent

Soon after GE's launch of the first fluorescent lamps in 1938, the range was extended to include different lengths and power ratings. The first of the 'miniature' types using narrow T5 16mm diameter glass was introduced in 1940, initially with a 9" lamp of 6W. The following year it was joined by the 12" 8W lamp and the smallest rating of 6" 4W.

The performance of small discharge lamps is always limited by the so-called 'end losses', an electrical phenomenon in which the volt drop (and hence power dissipation) infront of the electrodes is considerably greater than along the positive column discharge. The magnitude of this loss is roughly constant irrespective of lamp length - so for shorter lamps, end losses are proportionally higher. This limits the efficacy and light output of small lamps.

In an effort to overcome this problem, some of the earliest miniature lamps were produced with oval-section glass tubing. This caused the volt drop of the 4W lamp to increase from 32V to 38V - thereby reducing the relative magnitude of the end losses and yielding a more efficient lamp.

This lamp is made with calcium tungstate phosphor, whose blue emission extends partly into the UV-A region. Its purpose was to excite fluorescent dials of aircraft cockpits, and in this application by orienting the major diameter of the oval section towards the dials, it provided 2.5 times more flux than a circular tube. However the oval glass was difficult and costly to produce. It was replaced by a standard round-section tube as soon as the '360BL' phosphor had been developed, whose increased UV-A efficacy matched the output of this oval lamp in standard round tubing.
Manufacturer: General Electric Co. of U.S.A.
Lamp Power: 4 Watts
Lamp Current: 0.12 Amps
Lamp Voltage: 38 Volts
Cap Type: S14s Brass
Bulb Type: T-16 T-5 in eighths/inch
Bulb Finish: Blue CaWO4
Electrodes: Coiled-Coil (Ba,Sr)CO3 emitter
Discharge Length:
Atmosphere: Hg | Ar
Luminous Flux: ~40 lm (@ 100h)
Luminous Efficacy: ~10 lm/W (@ 100h)
Chromaticity Co-ordinates: CCx: 0.187 CCy: 0.196
Dominant Wavelength & Saturation: 477 nm 63%
Rated Lifetime: 500 hours
Warm-up & Re-strike Time: 2 minutes Instant
Burning Position: Universal
Nominal Length: 150 mm 6 inches
Factory: NELA Park, Cleveland OH U.S.A.
Date of Manufacture: 1941
Original Value: Unknown
References: 1) Fluorescent and Other Gaseous Discharge Lamps, W.E.Forsythe & E.Q.Adams, publ. Murray Hill 1948, pp. 96, 119-120, 186, 191-192, 197
2) Fluorescent Lamps, C.L.Amick, publ. McGraw-Hill 1942, p. 18
3) The Electric Lamp Industry, A.A.Bright, publ. Macmillan 1949, pp. 412, 501
4) GE Large Lamp Catalogue, USA, 1948, p.21