The bulb is too hot to restrike. Thats what the cooling off period is for. When the power goes out, then back on quickly, chances are you bulb will just glow a lil bit, you'll see a flicker inside as its trying to restrike.

This DRAMATICALLY shortens bulb life. Your best bet is to do as the instructions say, keep it off 15-20 minutes.
ninfan77 Reviewed by ninfan77 on . Digital Ballasts and Power Outages I have a 400watt Lumatek digital ballast (120V). I've seen people complain about power outages causing problems with air pumps and water pumps etc etc. What happens during an unattended power outage with a digital ballast? I only ask, cause I turned mine on for awhile, then turned it off to move it. Few minutes later plugged it back in and nothing happened. I turned it back off, waited. Did some snooping on the lumatek site and it says to wait 20-30 minutes after turning it off (power Rating: 5