Well, parameters such as CRI Kelvin temperature and even Lumens are completely worthless statistics for our purposes because they do not address the way in which plants use light energy. What these parameters do is they describe in objective terms how the light correlates to the way the human visual cortex perceives and interprets the world.
Kelvin rating and CRI are also not directly related. The Kelvin temperature of the bulb merely describes the way in which a theoretical "black body" would glow based on the amount of heat being absorbed and reflected by that object. For example imagine a block of steel in a foundry. It's probably easy to imagine that as you heat that block of steel the color at which it glows would change depending on how hot it is. In "black body" radiation lower temperatures radiate reddish and higher temperatures radiate more blueish . Medium temperatures would make the black body radiate yellowish.
This has little to do with, or is only indirectly related to Color Rendering Index which is a parameter that is more concerned with color fidelity. CRI is more useful in photography. In the example I gave in a previous post, lets say a blade of grass is green and that it reflects light at a specific wavelength, say 500 nanometers. If perfectly white light is shone against this grass then 500 nm wavelength is reflected and the grass can be perceived as that color. If reddish light is shone against the grass the reflected color will be a combination of 500nm plus higher wavelengths, say 600nm for arguments sake. Therefore when we look at the image, the composite color that we perceive the grass to be will be corrupted by the reflected 600nm red light. In making a bulb with high CRI the bulb manufacturer is attempting to add enough of other colors to the bulb's radiation that when shone against an object the native reflection wavelengths of that object being is not corrupted by the basic wavelength of the bulb. So in photography we sometimes want to capture the native wavelengths that our objects reflect. In a studio, if I'm taking a picture of a blonde person I want to capture that hair color, and if my flash is too red, the blonde hair color will be corrupted. So my flash needs to have a high CRI.
When we look at a lawn at high noon, much of the reflections are of blue light because full daylight has so much blue. But we know that a lawn is green so our visual cortex communicates with other parts of our cerebrum to filter out much of the blue - so the lawn is perceived as bright green. This combination of lighting plus cerebral manipulation, because it's so prevalent and overwhelming, then becomes the standard by which we judge all other lighting and is therefore called "neutral". Any light that subsequently reproduces or simulates this optical illusion is also judged to be "neutral" or natural. As a result, daylight at high noon has become our reference even though it's harsh and ugly.
Neither of these parameters have anything to do with the way plants use light energy. Plants can use any color light and they have mechanisms to reject harmful wavelengths such as UV. As long as the radiation is in the visible spectrum it can be used. Neither color temperature nor CRI has any effect on the plants and furthermore, neither of these parameters can tell us how pretty we as individuals will perceive the colors reflected in the tank.
There are a lot of myths out there about how blue wavelengths cause algae and how certain Kelvin temperature bulbs are more ideal than others. This is all complete rubbish. Vendors perpetuate these myths in order to program the population so that they can charge 30 quid for a light bulb. Now, certainly there are bulb phosphor formulations which produce wavelength combinations that many people find more pleasing than others. If one chooses to purchase these bulbs at a higher price based on aesthetics then that's fine, but we should be fully aware that we are paying money for something that pleases us, not because we are being duped into thinking that we are paying 30 quid because the bulbs are somehow "ideal" for plant growth. A 2 quid bulb from Tesco will grow the plant just as well but may not "look" as nice. 8)
Cheers,
easy, just light your entire world with those goofy pink bulbs and your central processing unit will make pink disappear. 8) 