Page 44 - Curriculum Visions Dynamic Book

(Above) A modern light bulb produced by machine techniques.
Light bulbs
One obvious reason for glass being used for light bulbs is that glass is transparent, but there are many other reasons. An ordinary (incandescent) light bulb gives out its light from a very hot filament. A material with a low melting point, such as a transparent plastic, would be unsuitable. The filament glows in a near vacuum. If it did not, the filament would react with oxygen in the air and burn away.
Glass is extremely strong under compression. The rounded shape of the light bulb ensures that the inwards pressure due to a vacuum or a gas at low pressure is evenly distributed, and the glass doesn’t implode.
Light bulbs can be blown into shape at very high speeds, often 30 per second using a single-piece mould. The filament
and leads are attached to
Glass bulbs
Blow holes
Moulds clamp around gob of glass
(Above) A light-bulb-making machine. A ribbon of glass leaves the rollers, and air nozzles push gobs of glass through the holes in the upper conveyor. As the gobs fall, moulds close around them, and then the glass gob is blown to fill the mould. The moulds then open and move away, leaving a bulb to travel further along the conveyor.
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