||Since the inception of the fluorescent lamp, its linear format has been regarded as an advantage in many applications - but in some cases has been a drawback. The first attempts to develop a more compact lamp can be traced to the invention of General Electric's Circline model in 1945. That was first offered in the 12" diameter 32W lamp, being joined in 1947 by a smaller 8" diameter 22W version, and prior to 1950 by the larger diameter 16" 40W. It did not take long for Sylvania to copy the tube-bending process and launch its own Circline lamps on the market, during the 1950s.
This early lamp has been made according to the original process, in which a small metal cup is sealed into each end of the discharge tube - visible in the detail photo in which the cap has been opened. The reason for this is not clear - perhaps it allowed easier manipulation of the glass during the tube-bending process. The cup is presumably made from an iron-nickel alloy, evidenced by the greenish-grey colour of the glass-to-metal seals. Tube bending was carried out simultaneously with the lamp exhausting process. On the vertical type exhaust machines the tubes are hung vertically by the exhaust tube protruding from one end, and pass though an oven which heats the glass to aid outgassing. For producing Circline lamps the ovens are operated hotter than normal, so as to soften the glass tube. Just as the glass begins to stretch and fall down under gravity, a pair of rollers pick up the lower end and coil the tube into a ring shape. The tube is then dosed with mercury and argon, and sealed off.
In later years the metal cup was omitted, instead forming the glass tube to a similar conical shape around the seal. Around 1975 the glass diameter was also changed from T10 to T9.