||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 calcium 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.