I stopped in here the other day while returning from nearby Phat Burrito in the hipster-heavy South End area. I didn't need any lighting fixtures or anything, but it's seemed like a cool store so I checked it out.
Indeed, the Modern Lighting Design Showroom is a cool store--packed with lights and fixtures of all varieties. And I really mean ALL--you can grab a light your grandma would own or one that your future self (as in 2029) would own. Some very futuristic/artsy stuff in here, so if that's your bag, definitely check it out.
I will say this: a lot of the items are pretty pricy. Like, way too much money for me to spend on a light. But I could see how you might wanna.