Neither crested geckos or Leopard geckos need special light however a leopard gecko will need heat UTH being the prefered way to go.
If the cage is 12 deep x 12 wide x 24 high it will be perfect for a crestie or gargoyle however not adequate for a leopard gecko.
If the cage is 12 deep x 24 high x 12 high it will work for a leopard gecko but not a crestie as they are an arboreal species.
Bearded Dragon, and BTS are out of the question with a cage that size a 2x2x4 will be needed for an adult.