Used in building lighting calculations, the Room Cavity Ratio (RCR) quantifies how effective a room or other interior area is at using the light from the fixtures contained therein. In turn, the specifier can then calculate the average illumination in a room. The RCR is almost never used in stage lighting, where incident light levels are more important.
The RCR can be calculated one of two ways, depending on whether the room is a rectangle or an irregular shape. For the following calculations, W is the width of the room, L is the length, H is the mounting height of the fixtures (not necessarily the ceiling height, such as for work lights on a stage), P is the perimeter of the room including interior partitions, and A is the area of the room.
For rectangular rooms, RCR=(5*H*(L+W))/A
For irregular rooms, RCR=(2.5*H*P)/A
Once the RCR is calculated, the specifier uses the Coefficient of Utilization (COU) to find the average illumination.
[There are also Zonal Cavities and Ceiling Cavities, but the most often used is the Room Cavity. Often, the Zonal and the Room will be the same number.]
The RCR can be calculated one of two ways, depending on whether the room is a rectangle or an irregular shape. For the following calculations, W is the width of the room, L is the length, H is the mounting height of the fixtures (not necessarily the ceiling height, such as for work lights on a stage), P is the perimeter of the room including interior partitions, and A is the area of the room.
For rectangular rooms, RCR=(5*H*(L+W))/A
For irregular rooms, RCR=(2.5*H*P)/A
Once the RCR is calculated, the specifier uses the Coefficient of Utilization (COU) to find the average illumination.
[There are also Zonal Cavities and Ceiling Cavities, but the most often used is the Room Cavity. Often, the Zonal and the Room will be the same number.]
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