Sometimes the power goes out. So I tell my daughter its like camping. But she was unimpressed with sitting in the dark.
I made my daughter an LED Campfire using 12 volt 10 Watt hi power LEDs. Flames are warm white, and daylight, and coals are amber/red.
LED's are current controled devices, we a constant current source. I chose the Buck-Puck 3021, which operated on 7-32 volts in, and provides 1000 milliamps (! amp) at about 12 volts (10.5 volts actually, but ideal for 12 volt 10 watt LEDs.
The unit needs to powered by batteries. 20 D-Batteries (1.5 volts nominal, up to 1.62v when new) provide about 30 volts but up to 32 volts wen new. Also, D cells are considered dead at about 0.8 volts; but 20 * 0.8 is still 16 volts, so the unit should be able to continue running beyond the point where the batteries might otherwise be considered "dead".
It turns out that the batteries lasted for about six months. When the battery voltage dropped below 12 volts, it ran for 24 hour a day for about five days straight and still lit the LEDS!. When I finally removed the batteries, five were below 0.35 volts, but 15 cells still read 0.95 volts (and are powering other projects).