For the oddly shaped aquariums, such as your corner, LED seems to e a versatile and quite efficient option. Since you only wan mushrooms and such, your lighting needs are easy. Yet anemones do require intense light in some cases... So I'm not sure how these two would mix.
If you want to go the economical route, DIY LED would be perfect. Look up rapidled.com, should be helpful in your search.
If you want a fixture, AI are certainly the top of the heap in LED, however you might not need that much light.
T5 and metal halide are always good options and well. T5 is my personal favorite, but I'm this situation I dont know your dimensions so I can't recommend anything.
Another thing to keep in perspective is at some point, will you want to start keeping corals or not. If you have a slight interest in tougher corals than say mushrooms... If might be a better investment to get a light capable of say SPS or LPS rather than buy a additional fixture down the road.
But anyways, in your situation, there are many choices. I'd recommend one 400 watt halide, or 6-8 T5's (whatever length fits your setup), or one AI sol hung up high. All of these will give you options.
Could you go into more depth on what you're looking for. Based on those options, what do you think? I'm more than willing to help, so just ask.
Others are sure to help as well here, so good luck!!!
