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Re: red light

In a message dated 98-07-02 04:07:09 EDT, Richard wrote:

<< It seems to me the easiest and cheapest way to make red is to
 get a high pressure sodium lamp. >>

The latest discussion of spectrum vs. intensity brings up an issue that has
been puzzling me.  My first plant tanks were lit entirely with incandescent
floods, because that's what I had available.  I had terrible algae problems
but my Rotalas were deep red.  I replaced the floods with a 175 watt, 5500K
metal halide when I set up a larger (70 gallon) tank, and the Rotalas now
refuse to redden even tip near the surface in the portion of the tank directly
under the MH.  Oddly, the red melon sword I recently bought is reddening as
expected. Has anyone discovered that red emmisions are critical for color
production in certain plants?  I would expect that anyone using JUST mercury
vapor lamps or 6500K fluorescents might have encountered this phenomenum, if
it exists.  Red light may be a good index of light intensity for some of the
photo responses at work in aquatic plants.  Since red light is strongest in
shallow water, it may "tell" the plant that reddening for protection from
excess light is needed.  So, do I put a small incandescent spot back on the
tank <G>?

Pete Mohan