||Since the inception of the fluorescent lamp, its linear format has been regarded as a great advantage in many applications - but in some cases has also been viewed as 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. Later developments led to U-shaped lamps. The original inventor of the U-shaped lamp is not known, but in view of their popularity in Germany as well as the extensive product ranges offered by the German lampmakers Osram and Narva, it is suspected that the design may have originated there. Osram produced its first U-lamps on 15th August 1949.
One of the advantages of the U-shaped lamps is that when built into rectangular panel-type luminaires, only half as many lamps are required as with simple linear tubes. Moreover since each U-lamp has roughly double the power of the short linear tubes, and the luminous efficacy of the fluorescent lamp increases with increasing length, the U-tube solution is invariably more efficient.
Osram manufactured four variants of U-tube fluorescent lamp. The first being a small T8 lamp of 16W, and the others being based on the popular T12 lamps of 2' 20W, 4' 40W and 5' 60W, U-bent at the centre. A special 65W version with different length was made for the UK market. Later, all types were replaced by krypton-filled T8 models.
This particular lamp is notable for its great weight, having been made from very thick-walled lead glass tubing, this material being easier to bend into a tight U-shape than ordinary glass types. It is coated with a standard calcium halophosphate material to deliver a cool white light.