Electricity

Artificial light is produced by converting electrical energy into visible spectrum electromagnetic energy. Therefore a knowledge of lighting requires an understanding of basic electrical terms and concepts.

The three main electrical terms are voltage, current and power. In order to understand these we can use a water analogy.

Voltage is similar to water pressure
Pressure is present behind the tap but is not doing anything (producing any energy) because the water is not moving. Pressure is required before there can be any water movement. The electrical equivalent of pressure is electromotive force, measured in Volts.

Current is similar to water flow
Pressure will cause water to flow and voltage will cause current to flow. The higher the voltage the greater the flow.

Unit of measurement is Amperes.

Resistance is similar to pipe diameter
Just as a small diameter pipe will restrict (resist) water flow (compared to a larger diameter pipe), a small diameter wire will offer more resistance to current flow than a larger diameter wire.

So resistance is the factor that limits current flow at any particular voltage.

The unit of measurement is the Ohm.

Power
Power is voltage multiplied by current (Volts x Amperes). Think of water coming out of a hose. If the pressure is high and the flow rate is high then the stream has power that can move things. Higher pressure and / or higher flow rates will produce more energy (power).

Unit of measurement is the Watt.