[APD] Re: myths/light

[Alan and Kim Van Nevel <van_nevel at verizon.net>]

>


George has it right in the last line, tanks with reflectors are a whole new 
story.  We have lots of smart people on this list, but the light intensity 
discussion continues to crop up from time to time.

A single point source has a intensity profile that falls off as 1 over the 
square of the distance (1/r^2, inverse square law)  Simple reasoning is the 
light is still providing the same amount of energy, but it is spread out 
over a greater area at longer distances, hence less intensity.

A linear source as George pointed out, falls off as 1 over the distance 
(1/r), but only for a infinite linear source.

Reflectors will induce loss.  I cannot think of any optical component that 
provides 100% reflectance.  Each bounce does incur loss.  But the amount 
for a good reflector is negligible for the benefit of redirecting all the 
energy that otherwise would have been lost radiating upward into the 
canopy.

If we really wanted to get ugly, we could do the modelling and calculate 
what the intensity profile would look like as  a function of position 
within the tank, taking into account the geometry of a reflector, how much 
loss the reflector induces, water absorption, reflections from the water 
surface, internal reflection from the glass walls etc, model it to the nth 
degree.

But to what end?  Either plants grow well within your setup for the 
conditions you have provided, or they dont, and we adjust tank parameters, 
plant selection, and nutrient levels accordingly.


> Message: 1
> Date: Tue, 7 Sep 2004 08:42:06 -0700 (PDT)
> From: "S. Hieber" <shieber at yahoo_com>
> Subject: Re: [APD] Re:myths/light
> To: aquatic plants digest <aquatic-plants at actwin_com>
>
> Doth not reflected light scatter too? And each bounce
> yields less light, no?
>
> Scott H.
> --- gbooth at frii_com wrote:
>
> > > Date: Sun, 5 Sep 2004 11:16:38 -0700 (GMT-07:00)
> > . . . Linear sources such as
> > flourescent bulbs
> > produce illumination that drops of inversely to distance
> > (twice as far
> > away, half as bright).  Also remember that this is in
> > "free space" without
> > reflectors.  Light with reflectors over a tank of water
> > is a whole
> > different animal.
>
>
> *********************************************

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