A lighting design specifies an average illuminance of 1 foot-candle over 100 square feet. No luminaire efficacy or light-distribution data are supplied. What electrical lighting power can be determined from these facts alone?
- AExactly 100 watts
- BExactly 200 watts
- The electrical power cannot be determined from these facts alone
- DExactly 1000 watts
Where to look it up
https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9
Why C is correct
One foot-candle is one lumen per square foot. The specified average illuminance over 100 square feet therefore corresponds to 100 lumens arriving at the area. Converting this into electrical watts requires the lighting equipment efficiency and how much of its light reaches the area. These data do not establish lamp power or emergency-lighting compliance.