Which lighting equipment is generally described as "a unit of light equipment"?

A luminaire is described as "a unit of light equipment" because it refers to a complete lighting unit that includes the light source, such as a bulb, along with other components such as reflectors and lenses. This term encompasses various types of lighting fixtures, including those used in theatrical settings, architectural lighting, and more. A luminaire not only illuminates but also contributes to the overall design and mood of a production by directing and shaping light, making it a fundamental element in stage lighting design.

The other terms listed do not have the same broad application or comprehensive definition as "luminaire." For instance, a parcan specifically refers to a type of lighting fixture often used in theatre for its ability to create strong, focused beams of light. The term "overlay" typically relates to techniques used in design rather than a specific piece of equipment. A moon box is a specialized light or fixture that simulates moonlight but is much less commonly referenced than luminaires in general discourse about lighting equipment. Hence, luminaire stands out as the correct choice due to its broad and inclusive definition in the context of lighting design.