Back to questionChoose “Save as PDF” in the print window.

SarkariResultOutBMS · 2024

Previous Year Question

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
  1. 5
  2. 1
  3. 2
  4. 4

Correct answer: B

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

RCR=5h(L+W)/(LW)=5×8×180/(120×60)=1.0

Step-by-step solution

RCR Calculation explanatory diagram

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.

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.

Quick method

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