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Lighting Fun

Michael Nielsen wrote:

>I was just reading some of Karen Randall's stuff on Aquarium frontiers and
>ran across a point I would like clarified by anyone who really enjoys
>lighting nitpicking.

If I'm responding, then that must be me.

>Randall states that blue light produces bushy, short plants, something I
>have read many times in the past.  Thinking that I would like my plants to
>have this growth I have an Actinic 03 bulb on one of my tanks.  The plants
>look the same as in other non-actinic tanks.  Randall then states later
>that the actinic bulbs are not really necessary for the planted tanks and
>are more appropiate for the reefers.

I can't say one way or another about the effect of blue light on the
morphology of aquatic plants.  As far as the use of actinic lighting goes,
I think this is something that creeped into plant keeping out of the reef
side of the hobby with no basis in plant husbandry.  It's just that the
one guy at the LFS who knows anything about lighting only really knows
about reefs and he gives the same recommendation to plant keepers that he
gives to coral keepers. 

>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...

Adey and Loveland (Table 1, p.117-118) list values that (converted from
meters) range from less than 2% per foot (Crater Lake, Oregon) to over
450% per foot (Lake George in Australia).  Just perusing their table I'd
guess that for nice, clear lake water something like 15% per foot might be
normal and adsorbtion over 30% per foot wouldn't be unusual. 

(This comes dangerously close to a "color of water in a white bucket"
discussion) ... The light at depth in fresh water (including our tanks)
probably isn't blue, because (again as Adey and Loveland point out) the
suspended particles and dissolved substances in fresh water do not adsorb
light like clear water or sea water.  The light at depth in freshwater
would be dim and yellow, red or brown - not blue except in the clearest of
freshwater lakes. 

Feel free to use actinic or other strongly blue light sources in your
aquarium, but probably you should do it for aesthetic reasons.  You
probably won't see a difference in the amount of light at the bottom of
your tank, you probably aren't simulating any plant-supporting freshwater
environment, and the plants you're growing might (or might not) respond to
blue light but they probably will not be dependent on a predominance of blue 
light in their environment. 

Roger Miller