In video production, scrims are metal wire mesh devices that are placed in front of a light source to reduce its intensity while also maintaining its color temperature and quality. They come in a variety of sizes and shapes but when used on set, they are commonly disc-shaped. When lights are dimmed, they can either become warmer or bluer depending on the type of bulb, but if this is an undesired effect, scrims are the perfect alternative.
Half scrims are useful in cutting down light in only a portion of a scene while allowing the full light to fall on everything else. This is useful in cases such as a glaring wall that is partially in a shot but it is the only thing in the scene where the brightness needs to be toned down. Using a half scrim with the mesh side located on the same side as the wall helps to reduce the harshness of the bright wall that results in more even lighting across the entire setting.
Scrims are typically color coded to signify how many layers of wire mesh are in it. A green scrim, known as a “single,” contains one layer of wire mesh, and it cuts the light down one half stop. A red scrim, called a “double,” contains two layers of wire mesh, which cuts the light down one full stop.
Learn more about how scrims work: