LIGHT

There are various ways that electricity can be used to produce light.
For example, we can heat a conductive filament or energise the electrons of a fluorescent gas.
We can use also an electronic device called a light-emitting diode (LED)

Incandescent bulbs.
When an electric current passes through the metallic filament of a light bulb, it produces light. This phenomenon is called incandescence.

Fluorescent tubes.
Inside a fluorescent tube, there is a metallic filament, normally made of tungsten. There is also an inert gas, such as argon, and a samall amount of mercury. When an electric current passes through the filament, electrons are emitted into the inert gas. 
These react with the mercury, creating invisible, ultraviolet light.
Then the phosphor coating inside the tube transforms the ultraviolet light into visible light.
Fluorescent tubes contain a number of toxic substances, such as phosphor and mercury.

Light-emitting diodes (LED)
A light-emitting diodes (LED) has layers of semiconductor materials. When electricity is applied to the LED, the electrons and holes cross over into the active layer, where they combine and produce photons, or particles of light.