Scubabum1983-If you are thinking of going with 15K XM's, you should should just go with the 20K XM's. 20K's have a higher par value than the 15K's. Although this really shouldn't be and there really isn't a reason for it, but that is just the fact when it comes to XM bulbs. Also, the 20K XM's have great par results, and also are probably your most white with a tint of blue 20K bulb out there. So if you were looking for an in between light color of bulb, try the 20K's and I think you will be very satisfied with them. Just my opinion