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# Re: Lighting Intensity

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Hi Rodney,

Perhaps you are new to the mailing list, but this topic has been discussed
extensively before.

I understand your arguement, but it's flawed in many ways.

>We choose a 1 m x 1m square area, hence, we have only 4 fluroscent tubes of
3ft
>length (imagine that over a 3 ft tank!).
>The light from a fluroscent tube is spread evenly across the 1m2 (1 metre
>square) tank, assuming the tubes are about 1 inch above the water.  In actual
>fact, I think you would get less intensity from the fluroscent lights as in
>close proximity with another tube, adsorption effects occur.

Most people do not arrange their tubes to cover a 1m x 1m area.  They pack
them close together for a smaller rectangular area.  And they use reflectors.

>In terms of lighting, there is the Inverse Square Law of lighting - the
>illuminance varies with inversely with the square of the distance i.e. the
>further away you are from a light source the lower the illuminance.  Also, the
>water absorbs light.

Many people on this list have pointed out that the Inverse Square Law
applies to point sources of light, not line sources which the tubes
approximate.  Light from line sources decrease linearly with distance, not
by the square of the distance.

Furthermore, you are not being fair by giving the MH a parabolic reflector
and none to the flourescent tubes.  Granted that you can't make a parabolic
reflector for the tube due to its shape, but you can make a linear-parabolic
reflector (a long reflector that is parabolic in the cross-section.  Many
people approximate this with gutter-like reflectors.  This will focus the
light even more and the drop off should be even less.

I agree that the reflector of a MH does a better job focusing the light than
the tubes can ever do, but with proper spacing and proper reflectors, the
tubes can do a decent job.  Of course, the amount of light at deeper than
18" also varies greatly with the power input (e.g., VHO vs NO), and tube
efficiency.  Many people are using flourescent tubes to light plant tanks
that are deeper than 18".

Hoa

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