This is the UV light your looking for unless they've come out with anything better in the last year or so, which I don't think so. LED isn't as adapted to these kinds of wavelengths as the t5's, there probably the most efficient within the range were looking for which is UV A+B in a specific ratio, and intensity.
I currently use 1 in my 4x4 between the panels, but I suppose I could put 2 in there and perhaps get a little more effect. But one does it pretty well. In the 2x4, 1 works really well also.
ā Fits all 4 ft. High Output T5 Fixtures, F54T5HO Lamp Type
ā 75% UV-B, 25% UV-A output