Or VaughnH, I really don't want to know your answer anyway since it's not important for me growing my plants

You have described exactly the theory behind the EI method of fertilizing. Like light, nutrient concentrations are not critical for growing plants. Having an adequate concentration is all that is needed, so long as you don't go way overboard, and weekly water changes take care of that problem.

As I said before, those who enjoy applying a more rigorous scientific study to growing plants should continue to do so. It is a hobby, so whatever aspects of that hobby make it more enjoyable are the aspects you should do more of. But, those who just want to be able to grow healthy aquatic plants and have an attractive aquarium, should not be misled into believing that scientific accuracy is a prerequisite to accomplishing that. (That's why we keep Tom around!)

True, its just that I without the knowledge of PAR/PUR-calculations wouldn't have figured out that the wpg-rule can be a bit misleading sometimes and also never gotten any feel for how little PAR/PUR we actually got in most setups. It is quite enlightening to dwelve into the details, and also fun.

But I agree, it's not needed in most cases to run a nice planted tank =)

Ah yes, that should work! But does such an optical filter exist that would be readily available to hobbyist? If your doing the conversion digitally then you need a meter that will take an entire spectral analysis - something thats probably out of reach for 99.99% of hobbyists. I've linked that aqua botanic light comparison many times, its a great source of info. But I question some of the data... like "I used only spectral curves and bulb data I was able to get from the web"... hmmm. And the bulb list there is a bit old.

Overall though, the main difference I see between PAR and PUR is that light in the green range isnt usefull much to plants so it can inflate PAR figures. But green still is usefull, it makes plants really 'glow'.

Amen !!! I've tested systems with clinical precision for years. All things considered I have enjoyed greater success with Basic EI !

Don't know why exactly, and honestly Don't Care ! If it ain't broke...Don't Fix It !!!

Common sense ain't so very common.

My main reason for being interested in this is due to the fact that I want to make sure I don't have somehting like I saw in a store. A 6700K bulb that had a huge spike in the Yellow/Green spectrum and hardly anything in the red and very little in the blue. Just wanting to get the best possible bulbs for my tank.

Does your fixture use straight pin bulbs? Would you want to try the GE 9325K 55w straight pin PCs? You could use two of these with two of your 6700K bulbs.

Here's two places that sell them:
55 Watt 20.7" 4 Pin Biax - Aquarium Fresh & Saltwater Phosphor: Light Bulbs Etc, Inc.
55W AQUARIUM BULB $14.19 F55BX/AR/FS GE 55 WATT 4800 LUMEN 9325K 67 CRI 20.70 INCH FRESH SALT WATER Atlanta Light Bulbs Inc.

That would describe most bulbs in the 6500/6700K range IME, I'm sure the Philips Daylight Delux bulbs I am using are the same way, as you can actually see some green tint to them barely, but many use them with success. Bulbs without very much green usually appear somewhere between pinkish and purple to your eyes. Like one bulb I tried, the Lightning Rod Aqua-Flora Plus, very little green according to thier little spectrum chart and the bulb is purplish.

Thanks for the links, but my fixture fails on both counts. It's a 4x96w SQ pin fixture.

Your options are much less with the 96 watt'ers, as I'm sure you already know.