The amount of light is governed mainly by Title 8, Section 3317 – Cal-OSHA. The minimum amount is half (.5 or 1/2) a foot-candle. This amount varies based on the location of the work being performed.
For more information on the topic, see these links:
In addition, the Human Factor Design Factors Book 2nd Edition goes over recommended light values for various concerns. See pages 334 and 335. Don’t have the book, get a copy on Amazon here http://www.amazon.com/Factors-Design-Handbook-Wesley-Woodson/dp/0070717680