When you burn a candle inside the votive, it illuminates the cell. It's a neat piece of film history and at $12, the votives are also affordable! Check out some of their Star Wars options:
To be on the safe side, I'd recommend only burning tealights or even flameless candles to ensure the heat isn't too much for the cell to handle.
Check out more options in the Actual Film Votive Etsy shop!