I've seen others use similar lamps, as is they have a tight pattern so 4-6" maybe, but if you can remove the bezel and take the lenses off, you can move them closer
I've seen some work well and others not so well. I think that has to do with many factors though, you have to find the right distance and use the correct run time for your system. Other things like screen quality (roughness) and flow will make a difference as well. All in all I think they are a good option. Try to make sure you are getting ones with mostly red, and all 660nm red (not 630nm)
Please update if you decide to use one of these. I have seen several LED grow bulbs that just screw into a normal lighting fixture. Seems like it would be an easy option when all you have to do it buy the housing with a clamp
I used one just like that or very similar. Worked well once I'd figured out how far away to place it. The light is quite focussed though so you don't get a wide spread.
I tried two of these lights before I made my own LED lights and they were both too weak. It was only 15 more bucks to make my own lights
