Bulbs have been used in electronics for along time and they are used in a wide range of circuits. Almost everyone has used a torch and if you look closely at the light source, it is more than likely that it is a bulb. In more recent years bulbs have been slowly replaced by LEDs as these are brighter, much more reliable, cheaper, energy efficient and have a much longer working life. They are also available in a range of colours. However, bulbs are still popular.