Secure some vellum behind the aperture - I've used some pretty patterned Christina Re paper but you could use plain, or draw your own design or print out a photo or clip art! Its important for a fair amount of light to get through, so use a fairly thin paper and don't add too much heavy colour.
Measure and fold half way along on the side panels. Measure the piece of card you'll need to fit the back (paper clip card in place, move the card to how you would like it to sit, then mark with a pencil to show where to cut).
You might want to use a metallic or gloss card to reflect more light. (I used shiny silver). Then add some decoration - I've kept it very low key with just three ribbon roses, but clearly you could add as much in the way of embellishment as you like. All that's left to do is to add a battery powered tealight candle. I WOULD NOT ADD ONE THAT INVOLVED FIRE - IT IS AFTER ALL MADE OF PAPER!!!!!!!!
You don't, of course, have to use an oval card - Regal Craft Cards have lots of different shapes available (everything from rectangles to dolphins!) or you can get blank three panel cards and use your dies to cut whatever shape you want.
I think this would not only be useful just as a card, but also as a placecard or decoration. I have plans (whether or not they'll translate to reality is a different matter) to print out some photos and make some to put on the dresser for Christmas