SUGGESTED LIGHT LEVELS: (footcandles)

Offices, Classrooms 30-100
Industrial High-bay 30-50
Manufacturing (on task) 30-150
Hallways, Corridors 5-10
Merchandising 30-150
Roadway 0.3-1
Baseball, home plate (PRO) 350
Indoor Parking 2-5
Outdoor Parking 0.5-2.0 

Illumination is measured in footcandles. One footcandle is the illumination one foot from a standard candle; 30 foot-candles (abbreviated fc) is thirty times higher. 

A typical light level for an indoor space is 30-50 fc. 

The human eye is very adaptable: full sunlight is about 8000 fc at noon; full moonlight is only 0.01 fc (one hundredth of a foot-candle!). If you reduce the light level people may adapt but there may be a cost. 

Lower light levels can lead to poor morale, reduced productivity, increased errors and so on.

There has been speculation that the human errors that caused nuclear problems at Three-Mile Island and Chernobyl could have been avoided if the light levels in the control room had been higher: workers would have been more alert, even at 4:00 a.m. Talk about the cost of poor lighting! 

There are intelligent ways of reducing energy costs (retrofit with newer technologies) and there are "not-so-intelligent" ways of reducing energy costs (simply remove one lamp from a 3-lamp fixture).