Lighting again (!!)
pmartin at netcom_com, discusses the near field effects, etc., of light. He is
entirely correct about light being electromagnetic radiation. My original
experience with the Law of Inverse Squares was with the design of "shortwave"
radio transmitting and receiving antennas. I like his description of "Gain"
in the focussing of light, etc. Well said. You can easily test this by first
using a well-focussed halogen flashlight with reflector in a dark room, then
remove the reflector. Same total amount of light, just not focussed.
Now, back to the effects of the bulb-to-illuminated surface distance in
lighting tanks. My illustration of the calculated difference in intensity of
a light at varying distances should properly have mentioned that I was
dealing with A SINGLE BULB. This makes a BIG difference! Why only a single
Here at the Aquarium Center we are dealing with a serious financial problem.
Our electricity rates were 7.5 cents per KWH for 20 years. Suddenly, without
warning, our rates were DOUBLED, to 15 cents per KWH. Our electricity costs
suddenly were running upwards of a thousand dollars per month. Worse, during
the Iowa State Fair, voltage drops to under a hundred volts were common.
Multiple tube fluorescent lights with tar magnetic ballasts simply
extinguished, and could not be restarted until late at night, when the
voltage rose. We are a pure non-profit organization, and ALL of our moneys
come from $2.00 admissions. People do not wish to carry flashlights to see
the fish! ( :-) ) They sure get grouchy when they cannot see the exhibits
after paying all of that money. (!!!!!)
The original lights were a foot - and sometimes quite a bit more - above the
water. Reflectors were white-painted metal. Dirty white paint, yellowed with
age and UV radiation from the bulbs. Plain old Shop Lights, the cheapest
they could get. Changing to single bulbs and simple aluminum foil
reflectors, laid directly on the glass, gave us a Law of Inverse Squares
increase in intensity. I measured the difference between 12 inches and 2
inches, and the results for a single bulb are closely in agreement with the
MULTIPLE BULBS STACKED CLOSELY SIDE TO SIDE WILL _NOT_ produce that dramatic
a difference in intensity when distance to illuminated surface is varied.
Well, at least not at the distances we are discussing. Put them outdoors and
vary the distance from, say, one foot to 10 feet from the illuminated surface
and - yessirree! - the old Law of Inverse Squares looks pretty darned good.
Take that really neat, high-tech Metal Halide with the super efficient
parabolic reflector, and suspend it a foot above the surface. Raise it 10
feet. Raise it 100 feet. Yep. The light intensity suddenly starts to fall
off at the Law of Inverse Squares rate.
So, let me introduce another question: Put your entire lighting system into
a "box" that has 100 percent efficient reflective interior. Cover closed.
_What happens to the light?_ Put ANY lighting system into the same box,
what happens to the light? Paint the inside of the box black. What happens
to the light?
Not a trick question. But food for thought. I am only trying to get a
suitable amount of light for healthy plant growth at reasonable cost. There
are lots of ways. Keeping the bulbs close to the surface sure helps.