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light intensities and latitude

  • To: Multiple recipients of list <iris-l@rt66.com>
  • Subject: light intensities and latitude
  • From: storey@aristotle.net (J. Michael, Celia or Ben Storey)
  • Date: Fri, 21 Feb 1997 16:24:50 -0700 (MST)

I haven't yet seen latitude discussed here as a factor to consider when
shopping for iris sources, and I wonder if it should be.

NPR reported recently that a film student took a light meter reading out of
doors at noon on a clear, sunny day in New York, NY, and came up with a
reading of 300-and- some-odd candle feet. The same week, a film student in
Los Angeles also took a light meter reading outside on a clear sunny day,
and his clocked 700-and-something candle feet. (Sorry I don't recall the
exact data, I was driving.) NYC is located at 40 degrees, 43 minutes N; LA
sits at 34 degrees, 4 minutes N.
This is a monster difference in light intensity, especially for living
things whose food production depends upon how well they absorb and employ
light energy.

Although it's a perfectly logical observation, I had not considered how
dramatically different light *intensity* (not merely duration) might be in
different regions.

Is there literature about the "physics" of iris acclimation to growing
conditions? Are plants that survive in dimmer, northern climes less
ambitious and productive, or does something in their foliage respond more
efficiently to light? Do they adapt by doing more with less or just by
doing less? Are they more like high-speed photo films or more like

Does brightness  play a huge role in how well iris hybridized in one locale
do when transplanted into  another?

storey@aristotle.net  USDA Zone 7b
Little Rock, Arkansas 34 degrees, 43 minutes N latitude... sorry I don't
own a light meter to report on our high-noon brightness, anyway  it's

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