1. According to the OSHA manual on preventing strain from working with video display terminals, three elements are of concern when it comes to lighting: 
 * quantity (lower lighting is better, OSHA recommends “28-50 foot candles”)
 * contrast (lower produces less strain)
 * glare (again, lower or more diffuse light is better)

  See: http://www.osha.gov/Publications/videoDisplay/videoDisplay.html

2. The American Optometry Association has similar recommendations on their website:</


  The AOA makes the point that if any of your work requires accessing other materials within your workspace, you will require a bit more light. 

3. While too much lighting can have negative effects, primarily due to glare as noted in Atwood’s quote, this does not mean that it’s best to work in complete darkness. Several studies have found that there is a lower level at which eyesight begins to be affected while using a computer. See Aaras, et al., 1998, Sugimoto, Ikeda, & Noguchi, 1999, and Wolska & Switula, 1999 for examples. 

  This question was answered by an information science student as part of the monthly <a href="http://answerboards.wetpaint.com/page/Slam+the+Boards!">Slam the Boards!</a> event:


Aaras, Arne, Gunnar Horgen, Hans-Henrik Bjørset, Ola Ro, and Magne Thoresen. 
     "Musculoskeletal, visual and psychosocial stress in VDU operators before 
     and after multidisciplinary ergonomic interventions." Applied Ergonomics 
     29, no. 5 (October 1998): 335-3554. Accessed November 9, 2011. 
     http://www.sciencedirect.com/science/article/pii/S0003687097000793 . 

American Optometry Association. "The Effects of Video Display Terminal Use on 
     Eye Health and Vision." American Optometry Association. Accessed November 
     9, 2011. http://www.aoa.org/x5380.xml. 

Occupational Safety and Health Administration. "Working Safely with Video 
     Display Terminals." Occupational Safety and Health Administration. Accessed 
     November 9, 2011. Last modified 1997.  

Sugimoto, S, I. Ikeda, and Y. Noguchi. "Estimation of physiological effects of 
     lighting by analysis of heart rate variability." Paper presented at the 
     24th Session of the CIE, Warsaw, June 24-30, 1999. 

Wolska, A., and Switula, M. "Luminance distribution on VDT work stands and 
     visual fatigue." Paper presented at the 24th Session of the CIE, Warsaw, 
     June 24-30, 1999.