Androv medical makes quality lights. Even though their page seems kind of shady.

The study (open-access PDF link in the article) says that in their testing on human skin samples, the 293 nm wavelength was the most efficient, and would require 10 times less exposure to get the same effect as the 305 nm wavelength. They seem to suggest that 30 seconds of exposure with the 293 nm wavelength lamp might be the equivalent of 30 minutes of sunlight.

The PDF also says that D3 is produced from lights all the way up to 320 nm, so the 311 ones sold on Amazon would work. But given the 293 vs 305 effectiveness, how much exposure would you need to actually make a meaningful difference? Probably a lot!