The sun is 5,800k, and 4,000 is too yellow and unnatural. 6,500 has quite a bit of blue, which is what I like as a autobody & paint man. Retired. We've been saltwater reef hobbyists since 1993 and we prefer 6,500k for corals and fish. Deeper water corals go from 10,000k to 25,000k, which are...