I have found these two apps earlier that are for generating normal maps from 2D sprites.
Sprite DLight is still in early access on Steam, but it looks very promising basically it says that with one click it can generate normal map from a 2D sprite. Check it out at at Steam http://steamcommunity.com/sharedfiles/filedetails/?id=340326626 or at its original Kickstarter project: https://www.kickstarter.com/proje...-maps-for-2d-graphics/description
The other one is already available to buy. It is called Sprite Lamp, but this one requires more work from the artist, if I got it right. It is available at http://store.steampowered.com/app/316830/
Maybe you could use one of them for next weeks' lighting programming. Although for getting Sprite DLight you may have to contact the author.