What are barndoors used for in lighting fixtures?

Barndoors are used to control the light beam emitted from a lighting fixture. They consist of adjustable flaps that can be opened or closed to shape the light, allowing the user to direct it more precisely and limit spill onto unwanted areas. This control is vital in theatrical lighting, as it helps in achieving the desired mood, focus, and visual clarity on stage. By adjusting the barndoors, designers can create sharper edges on the light or soften the beam, depending on the requirements of the scene.

The other options involve functions that barndoors do not perform. Changing the color of light is typically achieved through the use of gels or filters, while diffusion refers to scatter light to create a softer illumination, usually accomplished with a different type of accessory, such as a diffusion filter. Increasing heat is generally not a purpose of barndoors; instead, they focus on shaping the light output without directly influencing temperature.