My impression is that many people have no idea what the K or Kelvin rating on a bulb means. They assume that, like watts, the higher the K the better. So, 10,000 or 18,000 seems to be a much "better" number than 5500 or 6700. And, "actinic" sounds like a super dooper version of a bulb. Of course, higher watts aren't necessarily better either, but we still seem to view it as being better. After all the higher the GPH, the higher the gallons or liters, the higher the ppm, etc. the better, so why not watts and K? This sure isn't a hobby for those who don't want to work at learning things!