Hawksby, in 1700, was the first person to produce light using electricity from a glow discharge
in an imperfect vacuum. In 1810, Sir Humphrey Davy demonstrated a carbon arc at the Royal Institution
using a battery of cells and sparked the first enthusiasm for electric lighting.
This bulb is a GEC Osram 240V 500W ES cap theatre lantern bulb.
- The first filament bulbs used carbonised bamboo fibres.
- The anode of an arc light is consumed more rapidly than the cathode and so the cross-sectional area of the anode is usually about twice that of the cathode
- With a DC supply, it is not possible to sustain an arc between a cool cathode and an incandescent anode - the cathode must be incandescent but the anode does not.
- A filament bulb is evacuated to prevent loss of heat from the filament to the bulb by convection, not to protect the filament from loss by evaporation.
- The maximum practical filament temperature of a tungsten bulb is 2100C. With a coiled filament in a gas filled bulb the temperature limit is increased to 2500C
- Osram, an early pioneer in light bulbs, takes its name from the metallic elements osmium and wolfram (the German name for tungsten)
The lifetime of a modern bulb is often referred to as the burning time. Standard
domestic bulbs are generally
designed to be used either upright (cap down) or pendant (cap up) but not on their side
which shortens their life considerably. Many specialist bulbs have the correct position
printed on the bulb, for example, "TO BURN CAP DOWN".
This bulb is an Osram 230V 500W ES projector bulb with built-in reflector panel.
Most bulbs in use today have either a
bayonet or screw cap. There are various sizes in common use and while bayonet caps are popular
in the UK, screw cap bulbs are more usually found on imported fittings from Europe.
