Determine whether the light fills the stage or illuminates one area only. For light that fills the stage, describe it as a "general wash." For light illuminating an area, call it a "special." For light illuminating a single person or object, call it a "spot."
Determine the color of the light. Amber, pink, orange and red tones are to be described as "warm," while bluish hues are described as "cold."
Learn the areas of a stage. Stage left and right are to be described from the point of view of an actor looking at the audience. Up stage means the rear of the stage, while downstage means the front.
Determine how the lights transition from one cue to the next. When one set of lights fades out completely, leaving a dark theater, it is a blackout. When one set of lights fade out while another set turns on, it is called a cross-fade.
Put the ideas together. For example, "There was a warm special stage left to illuminate the bedroom scene, which cross-faded to a cool general wash."