I've done this with direct Sunlight and I do wonder if the cards have faded slightly as well. So I would say this lamp method is the only way really. I diden't leave the ones I did for more than 20 minutes in the sunlight and all the frosting had gone but I still think the cards lost a bit of colour.
This is a great method Poncho.
'But I was going to Tosche Station to pick up some power converters.'