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watts vs. lumens

Bob Dixon wrote:

>But with the high variablity in lumens per watt these days, that still doesn't
>really tell us anything.  I've tried to start a thread that deals effectively
>with this particular issue, but the responses I have gotten have been vague at
>best.  Can somebody define this rule-of-thumb in lumens per gallon or  per
>sqquare foot?  Yes, PAR would be eeven more effective still, but that is hard
>to detirmine based on the available info for the different types of bulbs.

But that's the problem.  Lumens are NOT a better measure than watts. Lumens
measure only the visible part of the spectrum, which is the part of the
spectrum least used by plants.  A lamp with good output in the areas of the
spectrum used best by plants can have a low lumen rating, and still grow
plants well. (Like purple-ish Gro-lux, etc.)  A lamp taht expendes most of
its energy in the visible range will have less of the wave lengths that
palnts use more efficintly, even though they look "brighter" to us.  

Whether we like it or not, without PAR ratings on a lamp, watts plus a
spectral chart are still as good as we're going to get for now when
guessing how a particular lamp might perform.

(and those high lumen output lamps will also work adequately if you use
enough of them)