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Rip Van Winkle wakes up and is blinded by the light

I've been reading all the recent lighting posts and began to wonder...

When did the Rule of Thumb (Lighting) go from "2-3 watts/gallon" to "2-4
watts/gallon"?  (Yes, yes, I know w/g sucks as a useful measure but, as
others pointed out, it's about the only thing most people can use).

Back in "The Olde Days", when there were no fancy fluorescent bulbs
available, one would strive for 3 watts/gallon with El Cheapo (tm) shop
lights in a cruddy non-reflector hood and 2 w/g when big bucks were forked
over for electronic ballasts or tri-phosphor bulbs or fancy mylar

We had a couple of 100 gallon tanks with four 40w Tri-Phosphor bulbs in
plain old white shop light "reflectors" with magnetic ballasts (that's 1.6
w/g, folks) and grew any plant we wanted at a rate that was almost too fast
to keep up with (pruning required every two weeks).

Now we have upgraded to 220w of AH Supply PC bulbs and reflectors (2.2 w/g)
and have more than enough light. We've cut the photoperiod back and we lined
the reflectors with aluminum foil (!) to reduce the light while the bulbs
were new. They're 18 months old now and we removed the foil.

Now I'm reading 4-5 w/g, overdriving bulbs to get the last lumen possible,
etc. What happened - have modern plants developed light resistance somehow?

Ah, progress.  Always "more is better". I long for the good old days.

George Booth in Ft. Collins, CO (gbooth at frii dot com)
  The website for Aquatic Gardeners by Aquatic Gardeners
      http://aquaticconcepts.thekrib.com (mirror)