Sylvania 240V 50W hardglass halogen lamps

Mains voltage halogen lamps were a popular more efficient replacement for incandescent lamps. The Halogen capsules were made in two distinct varieties: A quartz envelope and a hard glass envelope. Hardglass envelope lamps were cheaper to manufacturers as Hardglass has a lower melting point than quartz and is on its own already cheaper. However with time this advantage diminished.
Hardglass however is also less durable. While that is not a problem when the lamp functions normally, it may become problematic when the filament breaks. The breaking filament leads to arcing in the lamp, which itself causes a rapid expansion of the gas in the lamp and ultimately the lamp to violently rupture. This is especially likely on European 230V systems. Fuses may be used to limit the risk of shatter but they can not completely eliminate it. Therefor hardglass halogen lamps feature rather massive outer envelopes in order contain hot lamp fragments. The outer bulbs for this lamp for example were not made in a lamp factory but by a factory making bottles for perfume.

Eventually quartz halogen lamps become less expensive to manufacturer and technologies were developed were arcing could be limited in these lamps, making these lamps with their rather heavy and bulky outer envelope obsolete.