What different methodologies are used for Freshwater tanks?

[Anonymous]

beaslbob posted:

But you are just plain ignorant of how much they decrease with distance.

I don't believe I'm the one being ignorant here.

TAZ:

given a point source radiating equally in all directions. As you move further away a sphere around that source increases it's area. but the same amount of radiation is on that sphere. The area of that sphere is porportional to it's radius squared. So that if you double the radius you double*double time the area (4 times). With the same amount of radiation. Therefore the intensity is 1/(double)*(double). Hence the inverse square relationship. So the inverse square requires a source that radiates equally in all directions.

But a linear source like a NO tube does not follow that. It does not radiate in all directions. Add a reflector and further deviation is observed.

Just as we can adjust radio and tv antenna to get a station. If the antenna was just a point, it would make no difference how the point is rotated. By having long wires for antenna some of the reception is increase while other reception is reduced. So we turn the antenna to get the best signal. Because the antenna is no longer following an inverse square law. And, therefore, we can pick up weaker signals.

 

[Anonymous]

What sort of math is this?

 

[Anonymous]

it's not dissimiliar to the same math used in 'voodoo economics'


ignore beasle-as usual, he thinks he understands what he does not

 

[Len]

http://jamesc.net/bartlett-lighting/L01 ... ntals.html

The inverse square law (like twice the distance 1/4 the intensity) only applies to a point source. A line source it is linear (like twice the distance 1/2 the intensity).

Correct.

With an area source the intensity does not vary with distance.

Incorrect (for all intents and purposes pertaining to this discussion).

Practical experiences should tell you that the further away you stand from an artifical light source (regardless of type), the less intense the light source is. There are many reasons for this, ranging from simple attentuation to the concept that the further away you are from an artificial light source, the more it behaves like a point source. You are speaking in theoritical abstracts (such as black bodies).

All of the lighting I have seen in our aquariums are not point sources and therefore the inverse square law does not apply.

For practical purposes, metal halides are point sources. The ratio of distance fpr target measurement relative to the inner bulb's diameter greatly exceeds 5:1.

The question is how well the reflectors prevent the dispursion of the light. And how that dispursion compairs to the filtering of the light due to the water column. If the light sources cover the top area and produce a relative vertical column of light, then the only things affecting the intensity on the bottom is the length of the water column and the intensity of light.

I agree.

I totally disagree that WPG is a good or useful value.

 

[Anonymous]

Whooo hoo Len!

 

[Anonymous]

Assuming aninverse square relationship doubling the distance would mean 1/4 the intensity.

In the Feb advance aquariston this link:

http://www.advancedaquarist.com/2006/2/review

Sanjay Joshi, Ph.D., and Matthew Halloran give the flowing table when moving thereflector and bulb from 6" to 12" to follow in inverse square relationship law the light lost should be 75%

Table 4: Percent of PPFD lost from 6" to 12" from the lamp Reflector 3x3'
'


PFO Lighting new 400W/250W DE Reflector - 400W DE Lamp--9.5-- 18.5-48.7
PFO Lighting new 400W/250W DE Reflector - 250W DE Lamp--17.8-26.6- 54.6
Icecap 400W/250W DE Reflector --------------------------------- 7.8-22.5-43.6
Sunlight Supply - LumenMax-------------------------------------- 1.9-12.0- 26.3
Icecap 70/150W Pendant------------------------------------------10.9-20.9- 43.4


Values the are nowhere close to inverse square values.

Although hard to believe and not totall realizable in the real world, light from an area source does remain at the same intensity. Just as we can not find a totally point source that follows exactly inverse square relationships. but we can get close enough to be useful.

For instance a mh and most other sources are not really points nor areas but actually more like say a 5" thick line of light. so very very near the bulb like say 1.25 bulb diameters a meter would "see" an area of light. so when the meter is moved to say 1.30 bulb diameters the meter would read the same intensity. then further away the meter would "see" a line of light which would follow an inverse relationship. The as Len stated further out the meter would see a point source and start following an inverse square.

but all of that is based upon a bare bulb radiating in all directions with no reflectors.

When a reflector is added even the inverse square is thrown out.


Which means you can not simply assume and inverse square relationship and be done with it.

 

[Len]

Yup, the inverse square law is a theoritical ideal based on perfectly controlled conditions. Obviously, we approach no where near ideal behavior in uncontrolled conditions. And obviously, when you add a reflector into the equation, the law is no longer valid. But let's recognize all reflectors are terribly flawed, so you'll still see severely depreciating intensity the further away you move away from the artificial light source. The following statement seems at odds with this fact (a statement, which to be honest, I can't seem to grasp the full meaning of):

You are correct for greater deapth the light must be "brighter". but it will take the same amount of total light. Just there is less area to shine that light on. but the same of total light will produce the same intensity at the bottom.

I also don't understand what you are saying here:

imho one of the reasons watts per gallon is so popular is that as a given voluum becomes higher there is less surface area and therefore the same watts has to be concentrated in a smaller area. And is more intense to penetrate down the greater deapth.

Plus watts are easy to measure.

So with the assumption the amount of light per watt is the same it does make sense.

Amongst several issues I take with your proposition, watts is a virtually useless value. I can employ 5 billion watts to create one mere lumen.

Also, I am confused what you mean by saying metal halides are "a 5" thick line of light." Metal halides have an inner bulb where electricity is arc'ed through. In this inner bulb - which is about one inch in diameter - ALL the light energy is generated. At anything over about 5", any metal halide bulb begins to behave like a point source. All that outer glass you see is simply an encasement for the electrical wiring and parts required to strike the small inner bulb. Double ended halides are noticably smaller since they lack the outer glass envelope.

 

[Anonymous]

I think the problem here is that not all the factors are being looked at.

Beaslbob is saying that if you have a large shallow tank with a very large surface area and a certain wattage light which you then concentrate over a large deep tank with a small surface area, then there will be more wattage over a smaller area which will allow it to penetrate deeper.

The part I think that is being ignored is light decay due to attenuation of the water.

http://www.iscienceproject.com/labs/pdf ... nlight.pdf


Here is an experiment for you to run if you want to prove your theory right Beaslbob. Its fairly easy to set up, you just need the meter.

 

[Len]

Oh, if that's what he's saying, then the basic premise makes common sense. But then again, his supposition is assuming light is effectively refocused with the proper (custom) reflector so that the light energy is concentrated to the smaller area.

 

[Anonymous]

in the real world, he's wrong :wink:


you cannot achieve the same intensity of light if the source remains constant, but the water column depth changes-period.

you cannot achieve the same intensity of light if you increase the distance between the source of light and the object, REGARDLESS of whether or not the light is a point source-period.

 

[Anonymous]

As stated in my original post here, there is some validity to the watts per gallon idea. All I am saying is that say you got a 55g with 150W MH actinic. And want to go to say 150g. So 450W MH actinic should put you in the ball park.

If in both tanks the light is focused so that 90% or more of the light covers 90% or more of the bottom you should be ok.

So that the watts per gallon has validity as a general rule of thumb.

Considering blue par instead of watts possibily more.

Considering what type of tank even more.

But still there is some validity to watts per gallon as a general get you in the ball park rule of thumb.

Meanwhile Knuckle wanted to help a friend with FW. My sand plants light fish approach has been verified by another poster here with a link for referece.

I hope that will help knuckle's friend.

 

[Anonymous]

the best thing for knucklehead to do to help his friend is to make sure beaslbob never EVER has the opertunity to give him advise.

With an area source the intensity does not vary with distance.

you grasp of elemntary physics is almost as wonderful as a meercats grasp of cold fusion.

by that rational, an area light source will have the same light intensity at 20feet as it does at 1000 feet, therefore, a single area effct light source, according to you, can light the entire planet?!

did it not occur to you that an area light source is just a number of point light sources ACTING IN CONCERT?!

you ineptitude never fails to astound me.

see what you have done? you are the first person in nearly 10 years to make me loose my cool.

 

[Anonymous]

Then I suggest you take a deep breath and relax.

The point, line, and area sources are never exactly realized in the real world. Along with most basic physical things. But they are useful to predict within experimental error what will happen then let the engineers design real world stuff.

May I suggest you do further research and even check with say a high school/college physics teacher/professor.

And ask them

What is the intensity of light (or anything else) vrs distance for:

1) a point surce ratiating in all directions (ans inverse square)

2) an infinite line of infinte point sources radiating in all directions (line)

(ans inverse)

3) an infinite area of infinte point sources radiating in all directions (area)

(ans constant)

Back to the real world, you weigh the same on the first floor of your house as in the basement or second floor. Yet gravity follows an inverse square relationship. But for measuring gravitation force with common equipment and distances at the surface of the earth, the assumption of an area source produces more accurate results than the assumption of an inverse square.

Yet the inverse square is more appropriate for the earth-moon forces.


I realize this may be a hard concept to grasp but it is very basic high school physics. And was demonstrated in my high school physics class many years ago.

my .02

 

[Anonymous]

Then I suggest you take a deep breath and relax.

The point, line, and area sources are never exactly realized in the real world. Along with most basic physical things. But they are useful to predict within experimental error what will happen then let the engineers design real world stuff.

May I suggest you do further research and even check with say a high school/college physics teacher/professor.

And ask them

What is the intensity of light (or anything else) vrs distance for:

1) a point surce ratiating in all directions (ans inverse square)

2) an infinite line of infinte point sources radiating in all directions (line)

(ans inverse)

3) an infinite area of infinte point sources radiating in all directions (area)

(ans constant)

Back to the real world, you weigh the same on the first floor of your house as in the basement or second floor. Yet gravity follows an inverse square relationship. But for measuring gravitation force with common equipment and distances at the surface of the earth, the assumption of an area source produces more accurate results than the assumption of an inverse square.

Yet the inverse square is more appropriate for the earth-moon forces.


I realize this may be a hard concept to grasp but it is very basic high school physics. And was demonstrated in my high school physics class many years ago.

my .02

your previous posts on the subject have already proven to all YOUR complete ignorance of the same

 

[Anonymous]

And I see you are not equiped to correct that ignorance.

So I guess the readers can determine for themselves.

 

[Anonymous]

er-i've already done so in previous posts-especially re: the inverse square law-which you STILL didn't get at the time

stop bs-ing everyone by bluffing at a contended 'non-answer' by me- anyone who does a basic search will laugh at you ad infinitum for your pathetic lies at an attempt to make yourself seem more knowledgeable than you actually are

 

[Anonymous]

...


if you take the tank and stand it on end-the amount of wattage needed to get the same amount of light to the bottom will be MUCH higher than if the tank is oriented 'normally' (12" of water depth, versus 48" of depth)

maybe i'm missing something from your explanation ?

I think knuckle got it right. And I probably got lwh turned around.

You are correct for greater deapth the light must be "brighter". but it will take the same amount of total light. Just there is less area to shine that light on. but the same of total light will produce the same intensity at the bottom.

and again just a rule of thumb. for instance 40w NO tubes can vary from 900-3,300 lumens but still only have 40 watts. So other factors have to be considered also.

the inverse square law makes you sooooo wrong, it's beyond humorous

that's one

 

[Anonymous]

http://www.reefs.org/phpBB2/viewtopic.php?t=60020

more can be found there-and all should compare gpodio's pics to beasle's


(just to get a clue as to who really DOES know what they're talkin' about

the difference shown between a proper planted tank and a cesspool is stellar

 

[Anonymous]

I realize this may be a hard concept to grasp but it is very basic high school physics. And was demonstrated in my high school physics class many years ago.

that is so patronising it is untrue. i take it you didn't take your physics past high school level?

at the moment, i am considering going to A level in all three sciences, from the AS i already have in physics, biology, chemistry and maths, with the idea of taking science further, but am not sure which one, therefore before you start throwing BS like that around, CHECK YOUR FACTS. i realise that may be a hard concept for you to grasp, but it is very basic in not making you look like a chump

 

[Anonymous]

on this link

http://www.cis.rit.edu/class/simg712-90 ... agation%22

I found this summary:

Since energy is conserved, the total energy
in the wave must equal the energy emitted by the source, and therefore the energy
density (the energy passing through a unit area), is constant for a plane wave.


...

If a wave is emitted from a line source, the wavefronts are cylindrical. Since thewave
expands to fill a cylinder of radius r0, the wavefront crosses a cylindrical area that
grows as Area = 2πrh ∝ r. Therefore, since energy is conserved, the energy per unit
area must decrease as r increases:


...
The wavefront emerging from (or collapsing into) a point is spherical. The area the
wave must cross increases as x2 +y2 +z2 = r2 (area of sphere is 4πr2). Therefore the
energy density drops as r2

I don't mean to be patronising but on the web and especially with these posts above I was trying to dumb it down. I do have high school and college physics and chemistry along with 4 years HS math and 4 years college math for my aerospce engineering degree. Plus an mba. Plus three air force tech schools in electronics.

But I was not a physics major and it has been a few years since I used most of that stuff.

What I think is really "fun" is people who don't like my pictures of an aquarium, Dismiss basic physics concepts based on that.


And FWIW all of the above equations are based upon the inverse square law.