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Sue wrote:

>I haven't yet figured out why, because the "Super Daylights" put out more
>lumens and a whiter light. Could the less compact growth of stem plants be
>to the difference in spectrum? I was under the impression from reading this
>list, and other information, that spectrum isn't as important as the total
>output of lumens. 

Yes, it may very well be due to a difference in spectrum.  Blue end light
encourages short, bushy growth while red end light encourages tall growth.  

On top of that, lumens don't really tell us much about how a particular
bulb will grow plants.  Lumens relate to how much light the human eye
perceives.  And the part of the spectrum we see best is that part that's
least useful (though not totally useless) to plants.  Probably the best
measure of how a bulb is likely to perform is "PAR" (photosynthetically
active radiation) but this is not a value that is easily obtained for most
bulbs.  Even if you have _that_ you still need to look at the spectral
curve for the light in question to evaluate it's possibilities.  

The bottom line is that if you have _enough_ light, no matter the lumens,
watts or spectrum, your plants will grow.  With too little, it doesn't
matter how good the other factors are.

Karen Randall
Aquatic Gardeners Association