Input: Electric current.
Output: Light and waste heat.
These are common bulb circuit diagram symbols. The one with the cross is the British standard symbol.
A bulb is an output transducer that converts electrical energy into light and unwanted waste heat.
The current flowing in a thin tungsten filament causes it to become white hot.
The bulb resistance increases as it heats up.
Bulb LED Comparison
Bulbs are not very energy efficient
Bulbs are not very reliable
LEDs are far more efficient
LEDs are far more reliable
LEDs are much more expensive (last updated in 2015) but getting cheaper.
TOTAL RUNNING COST - LEDs work out cheaper after a few years.
A large department store might save thousands of pounds on their power bill after switching to LED spot lights.
Bulbs are used for ...
Illuminating dark areas
Signalling e.g. traffic lights, railway signals, brake lights, indicator lights, many more ...
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