Compared to a conventional magnetic ballast, an electronic ballast allows you to replace a 400W probe start lamp into a 320W pulse start lamp. Resulting in energy savings of 27% due to the ballast efficiency and improved lamp design.
What you get in addition is a light increase from 20 to 40 foot-candles. By adjusting the light levels to the required 20 foot-candles you will bring the total energy saving up to 56%.
With sensor control as occupancy sensing and daylight harvesting you can tailor your lighting system even further, pushing the total savings towards a mind blowing 65%.