Once your tank has been established for sometime and stable, there are some corals and such that do not require special lighting.
Certain types of polyped corals, gorgonians and other filter or solid food animals that do not require light for the purpose of maintaining zooxanthellae. Something to look into for later. The only concern with these types of animals is they are very high maintenance and require alot of care and special feeding. Not to be entered into lightly if you do not have the appropriate time and patience.