Recently we have been really lucky with the electricity; last year we were having semi-regular power cuts, and very regular dips in the voltage, enough to cause electrical equipment to turn off. One UPS died, but we didn’t need to get the candles out for long, as we found a new one quickly. If you choose a UPS that only just powers enough juice for the PC and monitor, you obviously can’t expect to be able to plug in additional items, but if you over-specify the unit, you can get away with a low-energy light bulb (in the range of 10-15 watts instead of 60watts, basically) for those times you need to see what you’re doing.