F14T12 with Zinc Beryllium Silicate Phopshor
At the time of the GE's launch of the first commercial fluorescent lamps in April 1938 the range comprised only four variants. A little later that year the fifth version emerged, in the form of the 14W lamp measuring 15" x 1.5" featured on this page. From the electrical standpoint it marks an interesting departure from earlier lamps, because instead of being developed for operation on the ordinary mains voltages, it was intended for operation on the 64-volt circuits of American street-rail cars. As such the discharge voltage is unusually low at only 41 volts.

That design feature led to an unexpected application in general lighting, owing to the fact that two lamps could be operated in series on the typical 120V American supply. One percieved obstacle of fluorescent lamps in the early days was their great length, but a two-in-series concept allowed the length of the luminaire to be halved and the F14T12 pairs rapidly gained popularity in decorative wall, floor and bracket lamps. The system cost was dramatically lowered by eliminating the traditional ballast, when it was discovered that two lamps in series could be ballasted by a 60V 30W incandescent lamp - which was offered for many years specifically for this purpose in a small S-11 sized bulb having an intermediate E17 screw cap and a white coated bulb.

This particular lamp is a very early version which uses the same luminescent compounds as the original fluorescent lamps, namely a combination of the pale yellow fluorescing zinc beryllium silicate and the blue fluorescing magnesium tungstate. Adjustment of the relative ratios of each adjusts the colour temperature. A "Daylight" 6500K variant was also marketed, having relatively more of the second phosphor.
Manufacturer: General Electric Co. of U.S.A.
Lamp Power: 14 Watts
Lamp Current: 0.37 Amps
Lamp Voltage: 41 Volts
Cap Type: G13 medium b-pin Brass
Bulb Type: T-38 T-12 in eighths/inch
Bulb Finish: White (ZnBe)2SiO4:Mn and MgWO4
Electrodes: Coiled-Coil + Anode Plates (Ba,Sr,Ca)CO3 emitter
Discharge Length: 305 mm 12 inches
Atmosphere: Hg | Ar
Luminous Flux: 490 lm (@ 100h)
Luminous Efficacy: 35 lm/W (@ 100h)
Maximum Brightness: 4600 lux 1340 foot-lamberts
Colour Temperature & CRI: CCT: 3500K CRI: Ra 72
Chromaticity Co-ordinates: CCx: 0.405 CCy: 0.391
Rated Lifetime: 1500 hours
Warm-up & Re-strike Time: 2 minutes Instant
Burning Position: Universal
Nominal Length: 381 mm 15 inches
Lighted Length: 343 mm 13.5 inches
Factory: Jackson MI / Bucyrus OH U.S.A.
Date of Manufacture: 1945 4th Quarter Date Code: MAZDĀ
Original Value: US $0.75
 
References: 1) GE Lamp Catalogue, USA, 1948, p.21
2) Fluorescent Lamps, C.L.Amick, publ. McGraw-Hill 1942, p.2, 16, 18.
3) Fluorescent and Other Gaseous Discharge Lamps, W.E.Forsythe & E.Q.Adams, publ. Murray Hill 1948, pp.186
4) Photometric measurement of lamp