If you are very worried about it and have $50-100 to spare, go get a UPS. Make sure you take into account the 400w size when you pick one out (the bigger the unit, the longer it will power your light). You should be able to get somewhere between a half hour to an hour out of one.

These devices are also very nice for air pumps in DWC setups.
gainesvillegreen Reviewed by gainesvillegreen 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