Lumens is another area of common confusion. Wattage is the "power" of the tube. Lumens are the actual amount of light being "radiated", or the amount of light energy reaching the animals created by the power output of the tube. Wow, now I'm confused!
Actually, let's equate it like this: Consider a shotgun blast. The number of pellets or "shot" that reach it's target is directly proportionate to the muzzle velocity of the gun that is it's source. The magnum shell will deliver more shot to it's "target" than a regular or low-brass shell because of the muzzle velocity. So does the VHO tube over the NO tube. More LUMENS, (or "shot") reach the animals (or "target") than an NO tube, because of wattage (or muzzle velocity). So LUMENS equal the light energy that WATTAGE delivers! This is naturally a gross over-simplification, but I think it works.
About CRI, or Kelvin
CRI is the manufacturer's gauge for the type of light that the tube emits.Type of light? Sure! Did you ever notice that warm white looks yellow compared to cool white in your kitchen ceiling fixture or over your workbench?
This is due to the formulation of phosphors used during the construction of the tube. See how color temperature relates to the "warm white" and "cool white" labels? All well and good for your office or home, but not nearly good enough for our corals and inverts! Hence we rate our tubes by K, and that other thing known as wattage. K stands for Kelvin, or the color temperature, another confusing term for CRI. As a general rule, aquarium related fluorescents in regard to reef habitats should not fall below the 5500K rating.
Please keep in mind that different companies use differing terminology for the same thing. CRI, K, Spectrum, Color Temperature, etc., all refer to the type of light their products produce. Actually, there are sound reasons for using differing names or labels, copyrighting being amongst the most common. Just like car companies use "4X4" or Quad Drive, it still means the same thing!
Basically, and without getting into a deep science seminar, the lower the Kelvin, the more yellow the light. Hence, the higher the Kelvin, our light appears starkly white or blue-white. Getting way up there into the 20,000K range, the bulbs actually appear to glow dark blue! Shades of the blacklight craze! Oh no, don't EVEN go there! Blacklight has tons of that nasty ultraviolet, and our animals don't like that at all! Save it for the bowling alleys or fuzzy posters!
Why Are Differing Kelvin Ratings Necessary?
Why are differing Kelvin ratings necessary at all? In a word, DEPTH! The natural reef environment begins at the surface and can reach to depths down to 150 feet, or more!.
If you have ever snorkeled or scuba dived, then you're aware of how quickly water depth can effect light intensity. The lower one goes, the dimmer and darker the light, turning from turquoise to azure to cobalt in very quick order. This obstacle haunted the hobby in it's infancy until Philips and other tube manufacturers realized that there was a dollar or two to be made in this hobby! Once it became economically feasible, tubes strictly for our tanks suddenly began appearing in magazines and our stocklist shelves. Holy reef tank Aquaman, I can now keep that once delicate specimen thriving in it's little glass box for more than a month or two!
Seriously, the K rating, or CRI, gives you the ability to match the tank lighting to that of your animal's natural habitat. Without this important advances in the industry we could never hope to duplicate lighting conditions at DEPTH in our living rooms, and provide as near identical conditions for our corals and inverts as that in nature.
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