Light generation
Basically, there are three ways in which electricity can be used to produce light: thermal radiation, low-pressure discharge and high-pressure discharge.
Thermal radiation
Current is passed through a wire to heat it to high temperature. The model here is the sun with its surface temperature of 6000 K. Because it has the highest melting point of any metal (3683 K), the element tungsten is best suited for this purpose. Examples: incandescent lamps and tungsten-halogen lamps.
Gas discharge
A voltage is applied across two electrodes in a glass enclosure filled with inert gases, metal vapours and rare earths metals to produce an arc discharge. The direct radiation from the gaseous filler substances combines to produce the desired light colour. Examples: mercury vapour, metal halide and sodium vapour lamps.
Luminescence
The invisible UV radiation generated in mercury gas discharge lamps is converted into visible light by phosphors. Examples: fluorescent lamps and compact fluorescent lamps. The process by which electricity is directly converted into light is electroluminescence. Examples: Light Emitting Diodes (LEDs).
Basically, there are three ways in which electricity can be used to produce light: thermal radiation, low-pressure discharge and high-pressure discharge.
Thermal radiation
Current is passed through a wire to heat it to high temperature. The model here is the sun with its surface temperature of 6000 K. Because it has the highest melting point of any metal (3683 K), the element tungsten is best suited for this purpose. Examples: incandescent lamps and tungsten-halogen lamps.
Gas discharge
A voltage is applied across two electrodes in a glass enclosure filled with inert gases, metal vapours and rare earths metals to produce an arc discharge. The direct radiation from the gaseous filler substances combines to produce the desired light colour. Examples: mercury vapour, metal halide and sodium vapour lamps.
Luminescence
The invisible UV radiation generated in mercury gas discharge lamps is converted into visible light by phosphors. Examples: fluorescent lamps and compact fluorescent lamps. The process by which electricity is directly converted into light is electroluminescence. Examples: Light Emitting Diodes (LEDs).