What different methodologies are used for Freshwater tanks?

[Anonymous]

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.

Whether we should measure lumens or par is another question. And there are great differences among say 4' NO tubes lumen's even though they when the have the same 40w rating. Not to mention what K they are.

 

[Anonymous]

There is some good stuff in this thread, thanks!

 

[Anonymous]

imho one of the reasons watts per gallon is so popular is that as a given voluum becomes higher there is less surface areaand 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.

Whether we should measure lumens or par is another question. And there are great differences among say 4' NO tubes lumen's even though they when the have the same 40w rating. Not to mention what K they are.

explain please

 

[Anonymous]

I thought I already did. :lol:

Anyrate let's run some numbers

Take a 48"x20"x12" tank.

and say 160 watts


top is 48x12=576 sq inches. light intensity is 160/576 watts/sqin=.27777777778watts/sqin. 20" deap. .0277777watts/sqin/20"= .013888888889 Brightness/in deapth

Now tip it so it is 12" high

area is 48X20 960sqin. for 160/960 watts/sq in 1/6watt/sqin to light up 12" for .013888889 brightness/in deapth

tipping it so it is 48" high

Area is 12x20=240 sqin. for 160/240 watts/sqin. .66666667. for a deapth of 48". For 0138888889 brightness/in deapth.

So for the same volume and the same amount of light spread over the entire top area, and assuming the same filtering of the light through an inch of water, the bottom of the tank receives the same amount of light.


Of course in one case NO may suffice, Another PC's and another MH for that to happen.

Lotsa assumptions more has to be considered. But the above does show there is a somewhat valid reason for a very general rule of thumb for watts per gallon or par/gallon or lumens/gallon, etc. etc.

 

[Anonymous]

science is cool and all. sometimes you just gotta approach it like gardening tho ...

 

[Anonymous]

I thought I already did. :lol:

Anyrate let's run some numbers

Take a 48"x20"x12" tank.

and say 160 watts


top is 48x12=576 sq inches. light intensity is 160/576 watts/sqin=.27777777778watts/sqin. 20" deap. .0277777watts/sqin/20"= .013888888889 Brightness/in deapth

Now tip it so it is 12" high

er- i thought the tank already IS 12" high.(lxwxh)

area is 48X20 960sqin. for 160/960 watts/sq in 1/6watt/sqin to light up 12" for .013888889 brightness/in deapth

tipping it so it is 48" high

Area is 12x20=240 sqin. for 160/240 watts/sqin. .66666667. for a deapth of 48". For 0138888889 brightness/in deapth.

So for the same volume and the same amount of light spread over the entire top area, and assuming the same filtering of the light through an inch of water, the bottom of the tank receives the same amount of light.


Of course in one case NO may suffice, Another PC's and another MH for that to happen.

Lotsa assumptions more has to be considered. But the above does show there is a somewhat valid reason for a very general rule of thumb for watts per gallon or par/gallon or lumens/gallon, etc. etc.

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 ?

 

[Anonymous]

48" of light filtering vs. 12", you know

 

[Anonymous]

Vitz, I kind of understand what he is saying.

I am not saying he is right, I don't know.


He is saying that although the depth goes up, the surface area goes down so its a more intense light for the size of the top so to speak.

I have no idea if it works that way or not...

 

[FragMaster]

suface area is a none issue. Niether is depth,(to some degree any how)
were talking about fresh water here still right? So that means were talking about lighting for fresh water plants then right?
Halogen bulbs from wally world will work.
GREAT growth can come from HPS in the 5500k range as well.

 

[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.

 

[Omni2226]

Well for once bob is right about how things can work in FW tanks.

I kept 4 diffrent tanks ranging from 40 to 15 gallons with nothing but a heater. Plants, water gravel and fish. Lights were the cheapo aquarium lights that came with the tank. Heres a link to a good website about natrual aquariums.

If you read her FAQ you will see she uses no filters,heaters or anything else besides plants gravel and fish. For lights she uses shop lights with daylight full spectrum bulbs. But unlike bob she does water changes.

http://naturalaquariums.com/

 

[Anonymous]

onmi

thanks and excellent link. Independent confirmation of methods is always welcome.

Bob


Edit: as well as independent disproval of methods also. We can actually learn more from failures.

 

[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

 

[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

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


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

 

[tazdevil]

With an area source the intensity does not vary with distance

Bob, where do you get this idea? Regardless if it is a point or a spread source, the light intensity will decrease as distance increases. You don't even need to be an expert to understand this. The inverse square law does not apply to just point sources, I know this from radiation physics. Light and radiation do behave similarly, and the inverse square law applies to both. In different forms, yes, but the idea is the same.

 

[Anonymous]

With an area source the intensity does not vary with distance

Bob, where do you get this idea? Regardless if it is a point or a spread source, the light intensity will decrease as distance increases. You don't even need to be an expert to understand this. The inverse square law does not apply to just point sources, I know this from radiation physics. Light and radiation do behave similarly, and the inverse square law applies to both. In different forms, yes, but the idea is the same.

the object of that question needs to be in plural form :wink:

 

[Anonymous]

With an area source the intensity does not vary with distance

Bob, where do you get this idea? Regardless if it is a point or a spread source, the light intensity will decrease as distance increases. You don't even need to be an expert to understand this. The inverse square law does not apply to just point sources, I know this from radiation physics. Light and radiation do behave similarly, and the inverse square law applies to both. In different forms, yes, but the idea is the same.

Yes light is a radiation. And gravity follows the same rules.

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

Invere square applies only to point sources. Because they radiate in all directions. As in planets which are usually considered points because the distance between the two opjects is many orders of magnitude greater than the size of the two objects. But even then when a small object is near a larger irregulary shaped objcect like an astroid, the orbits are no longer simple elpises but highly complicated curves.

The above example of a point, line, area souce was a demonstration in my high school physics class designed to show exactly that point.

Lenses and reflectors specifically change the inverse square law for follow whatever properties they provide. They do that by redirecting the radiation usually sent in other directions. Thereby reducing the dispursion of the light and and increasing the intensity at distance.

Just because something is light or gravity it will not always be 1/4 as strong at twice the distance. In fact you will probably not measure that in real world applications. The closer you come to that observation, the closer you have observed a point source.

 

[FragMaster]

8O 8O

 

[Anonymous]

FWIW

Hope I didn't come across as negative with the ignorant comment above.

I don't consider being ignorant negative. It is impossible to have total knowledge in our heads of all that as been accumulated in the history of man. So we all have vast areas of ignorance. Which I am sure all will agree applies to me too. :lol:

So if someone was upset or hurt by the comment please accept my apologies and explaination. that was not my intent.

 

[tazdevil]

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.