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Re: Aquatic Plants Digest V3 #299

In a message dated 98-06-02 03:52:30 EDT, Roger responded to Michael:

<< >This was one reason I included the blue bulb, but also because the blue
 >light penetrates water better, thus getting to the substrate more.  Is the
 >water penetration really of any importance?  Does anyone know the
 >precentages lost in 24" (depth of tank to substrate)?
 This is extremely variable in fresh water.  How clear is your tank?  
 There's also variables depending on the density and type of planting and 
 a lot of odd details.  I think George and Karla Booth might measured some 
 real numbers.  But ignoring all that... >>

Hi guys,
     I don't think that loss of particular wavelengths is going to be much of
a problem  because the path length of the light through the water is very
short.  However, artifical light levels decrease with depth much more
dramatically than light would in a natural environment.  Since this is a
function of the inverse square law, it's a more serious problem with light
sources that behave more like a point source.  I've measured "natural" surface
light levels under a metal halide (1000 watt), only to find out that at a
depth of 30 inches the available light is similar to a 200 ft depth (that's
two zeros...no typo <G>). The fall-off in light intensity is least problematic
when the whole surface of the tank is covered with fluorescent lamps, but I
haven't measured the actual loss with depth. 

Pete Mohan