Practical Lights

What is a practical light?  How is it used differently than regular film production lights?  What is Bradford's advice in using them for film?

    A practical light is a motivated light source that the audience is able to see in the shot, such as a lamp, candle, screen, etc. Practicals are used differently than regular film production lights as the audience knows where the light source is coming from relative to the actors; thus, when the actor moves, the direction of the light maintains a fixed position, whereas production lights are more subjective in where they come from, which allows more movement. Bradford's advice in using them for film is to plan the placement and type of practicals based on the location and the blocking in order to effectively communicate the scene to the audience.