Interior Light Dimmer

I've looked for this around, but can't seem to find too much info.  Naturally, when I was NOT looking for it a few months ago I swear I saw it.

Anyway, I was wondering if anyone can tell me how to make my interior light slowly dim when I shut my door.  I'm looking for, say, a 5-10 second delay.  I'm assuming it will require a capacitor of some description, but as to the size and type, I'm not sure.

Any help appreciated.

This is the latest one I remember seeing:

https://www.the12volt.com/installbay/forum_posts.asp?tid=47908&PN=3

thanks... I guess thats the problem with keyword searches: unless you use the right words, you don't get what you need =)