You are 5x to 10x the real rule, depending on what kind of "construction area"
it is 5 FC in general construction areas, 10 FC in batch plants and electrical equipment rooms but as low as 3 FC if you are excavating, placing concrete or storing materials
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=1063050 FC would be a very brightly lit office.
