A very early light bulb and a quick-break light switch
A very early light bulb
Look closely at this light bulb made by Joseph Swan. At the top of the bulb is a spike or ‘pip’ where the air inside the bulb was pumped out to create a vacuum before the glass was sealed.
Inside the bulb is what looks like a loop of wire, known as the filament. In fact it is made of cotton thread and appears black because it was ‘carbonised’ – a process of heating it in a furnace. Carbon was one of the few affordable materials then available that could withstand the heat as electricity was passed through it.
Carbon caused bulbs to blacken and Swan developed a method to reduce this. Heating the filament as air was removed from the bulb improved the vacuum so that fewer carbon particles travelled from the hot filament to the cool sides of the glass.
Light at the flick of a switch
Fire was one of the risks of early electric lighting. People were used to gas lights that featured taps which could adjust the level of light by regulating the flow of gas. When they tried to adjust an electric light switch in the same way, electricity would spark between the points of the switch and lead to fires.
John Holmes designed this switch with a spring mechanism that snaps the switch to either an on or off position. This ‘quick break’ prevented electricity from arcing. The ceramic exterior of the light switch further reduced the risk of shock and fire.
1. Joseph Swan carbon filament lamp and holder, c. 1881
Inv. No: B5101
2. Quick-break light switch by John Holmes, patented in 1884
Inv. No: B5273
Source: Discovery Museum, Newcastle