The basic properties of light are:
Intensity
Direction
Wavelength or Colour
Polarisation

We can control the Intensity of conventional theatre lighting by varying the current through the lamp with a dimmer, or by using neutral density filters. We can control the intensity of discharge lamps such as those used in moving lights by using a mechanical dimmer or shutter.

We can change the Direction of light by using a reflective surface such as a mirror.

There are two methods of changing the Wavelength or Colour of light, Subtractive and Additive.
The Subtractive method uses a lighting filter or gel to only allow a narrow spectrum of light pass through the filter, the remaining parts of the light spectrum is dissipated as heat in the filter. The subtractive method was developed for conventional lighting. With the development of moving lights the subtractive method used Cyan, Magenta and Yellow dichroic filters or flags.
The Additive method uses the output of different coloured emtters to make up a desired colour. Initially there was Red, Green and Blue colours used, then White was added to get soft pastels for theatre and Amber was added to get strong saturated colours for musicals and bands.

Polarisation of light can be achieved by using polarising filters. it is used as a dimmer and for disco lighting.