Re: Leggy Plants and Light -- or - light inclinations

["S. Hieber" <shieber at yahoo_com>]

Rachel Sandage asked about AH Supply lamps' directivity:
 
> I'm also wondering about the directionality of the AH
> supply lights. The 
> plant in the photo is at the rear of the tank - there are
> no lights directly 
> above it. Are the AH supply miro reflectors so
> directional that a plant 
> which is 4" horizonally from the back of the reflector,
> and 4-12" below it, 
> will not receive enough light?


Yes and no.

Let me say that I always love Rachel's questions.  She
seems to ask basic things that I thought I knew, or wished
I knew, but don't.

It's not the fact that it's Miro (a brand name for a
plastic coated aluminum) that effects the directivity but
simply the angle of the bends.  For economy and
convenience, the AH Supply reflectors or shaped on a brake,
bending it with flat facets.  But it is meant to
approximate a parabolic reflector.  A parabolic reflector
redirects any light that doesn't leave the bulb and traavel
straight down -- it redirects it straight down. 
Fluorescents are very diffuse light sources and no
parabolic refelctor is perfect -- and no psuedoparabolic
reflector is near perfect.  

Turn off the lights in the fish room and have a friend or
two hold the lamp over the floor.  Start out a few inches
away and then raise the lamp and measure intensely lit area
on the floor.  This won't be as scientific as using a light
meter, but it will give you a good idea.  Over the water,
the light will be more diffuse than the lamp over the floor
-- the water surface gives much of the light an extra bend.

The other way to assess is to check whether the stem plant
keeps "leaning" over as it grows into the higher light --
this assessment is easily fouled by water currents.

At 4" back and 4" below, not enough light -- at 4" back and
12" below, I think it's in the path of the stronger light.

Scott H. 

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