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RCR Calculation

A room is 120 feet by 60 feet with 16 feet ceiling. A luminaire is suspended 4 feet below the ceiling and the work plane is 4 feet above the floor. The value of room cavity ratio (RCR) is
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Answer & Explanation
Correct AnswerB. 1

Quick Explanation

The luminaire is 4 ft below a 16-ft ceiling and the work plane is 4 ft above the floor, so cavity height is 8 ft. Room cavity ratio is RCR=5h(L+W)/(LW). Substituting h=8 ft, L=120 ft and W=60 ft gives RCR=1.0, matching option B.

Formula / Key Relation

RCR=5h(L+W)/(LW)=5×8×180/(120×60)=1.0
RCR Calculation explanatory diagram

Detailed Explanation

Correct Answer

B — 1

Concept and Reasoning

The luminaire is 4 ft below a 16-ft ceiling and the work plane is 4 ft above the floor, so cavity height is 8 ft. Room cavity ratio is RCR=5h(L+W)/(LW). Substituting h=8 ft, L=120 ft and W=60 ft gives RCR=1.0, matching option B.

Calculation / Key Relation

RCR=5h(L+W)/(LW)=5×8×180/(120×60)=1.0

Exam Takeaway

Use the vertical distance from luminaire plane to work plane as cavity height.

Common Mistake

Do not use the full ceiling height as h when luminaires are suspended and a work plane is specified.

Quick Trick

Use the vertical distance from luminaire plane to work plane as cavity height.

Common Mistake

Do not use the full ceiling height as h when luminaires are suspended and a work plane is specified.

Exam Tip

Use the vertical distance from luminaire plane to work plane as cavity height.

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