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For many years the halogen retrofit lamps for ordinary incandescent lamps that were produced by American manufacturers had a commercial weakness. Mains voltage low-wattage halogen capsules were first developed in that country for use in sealed-beam PAR type reflector lamps, and the lowest cost capsule that can be used in that embodiment is a type fabricated in aluminosilicate hardglass instead of the usual quartz. Hardglass is a cheaper material and can also be produced on higher speed machinery than quartz. Hardglass capsules are mechanically weaker and have an increased tendency to shatter at end of life, but that is of no consequence in the heavy-walled PAR reflectors. For use in ordinary non-directional lamps though, special heavy-wall outer bulbs had to be developed and the high cost of these negated any saving from the cheaper capsule. The European design of a slightly more expensive quartz capsule in a low cost soft glass outer bulb proved to be the more economical solution.
In 1996 following its takeover by Osram of Germany, the American Sylvania company therefore changed some of its lamp designs to the more economical quartz+softglass version featured here. The lamp is however not quite identical to the European versions and has been specially modified for the American market. The quartz capsule used is not a UV-blocking type and requires the outer bulb to perform that function. In case the outer would be broken and the capsule continues to burn there is a risk of UV exposure. In order to ensure that the capsule will extinguish in such cases it is operated in series with a small filament in the outer bulb which functions as an oxygen fuse, and will fail in case the outer bulb should break. |
