As a general rule-the lower the K value the higher the par rating. The higher the K value, you generally will have lower par (slower growth), but better coloration in your corals. Unfortunately it's a tradeoff. It seems you can't really have the best of both worlds. Drop me an email and I'll send you a site that tested a variety of bulbs in terms of par ratings, and also shows a pic of the color of each bulb. Personally I run XM 10k's (very high par rating) with 2 110w VHO super actinics. But it's all about what you want-color or growth.