...find a local 'dollar' or cheapie store, and pick up a buncha LED 'stick-em' lights... (the ones that are normally 8-9 bux at the WM or building supply store are buck-fitty knockoffs at the dollar store)...

and probably a buncha batteries, too, unless you're good with 5v DC power supplies.

As long as there's at least some light during the Period Of No Incoming Electricity, they should just interpret that 'day' as being a bit 'overcast'.