newfound77951
Aquarium Advice Addict
This came up in another thread, but I thought it might be very useful and didn't want to hijiack the other thread, so here it is....
There is a way to calculate the amount of light reaching the bottom of your fishtank without a light meter. It's called Beer's Law, some of you may remember it from high school chemistry or physics. The equation looks like this:
Iz = Io*e(-kZ)
In English:
Light at the bottom = light at the surface^(-1*depth of aquarium)
K is the extinction coefficient, and can roughly be assumed to =1 in this case (trust me)
Light at the surface is your light fixture's wattage
depth of the aquarium should be from the water surface to the substrate, but the height of the aquarium will do. It needs to be in METERS for the calc to work. (Watts are metric units)
This won't calculate watts per gallon at the bottom of the tank, per se, what it will tell you is the amount of light reaching the bottom of the tank.
Here is an example calc on my 55 gal with 192 watts of light:
depth is 22" = 56 cm or 0.56m
light at the surface = 192 watts
light at bottom = 192watts^(-1per m*0.56m) = 110 watts reaching the bottom.
You'll need a scientific calculator or Excel (not the plant food!) to do the exponent.
What this can do is give you an idea of how the depth of your tank is affecting the amount of light reaching the bottom plants. So using the 110 watts and 55 gallons, you could say that at the bottom of this tank the lighting is 2 watts "per gallon", compared to the 3.5 watts per gallon at the top. So the light intensity at the bottom of this tank is a little more than 1/2 what it was at the top.
Please let me know if you need help with the calcs...It would be neat to have a bunch of folks do this and see what we all get. I don't know how to "post" a spreadsheet but if someone knows, let me know and I'll make one up so that people can just enter their numbers.
There is a way to calculate the amount of light reaching the bottom of your fishtank without a light meter. It's called Beer's Law, some of you may remember it from high school chemistry or physics. The equation looks like this:
Iz = Io*e(-kZ)
In English:
Light at the bottom = light at the surface^(-1*depth of aquarium)
K is the extinction coefficient, and can roughly be assumed to =1 in this case (trust me)
Light at the surface is your light fixture's wattage
depth of the aquarium should be from the water surface to the substrate, but the height of the aquarium will do. It needs to be in METERS for the calc to work. (Watts are metric units)
This won't calculate watts per gallon at the bottom of the tank, per se, what it will tell you is the amount of light reaching the bottom of the tank.
Here is an example calc on my 55 gal with 192 watts of light:
depth is 22" = 56 cm or 0.56m
light at the surface = 192 watts
light at bottom = 192watts^(-1per m*0.56m) = 110 watts reaching the bottom.
You'll need a scientific calculator or Excel (not the plant food!) to do the exponent.
What this can do is give you an idea of how the depth of your tank is affecting the amount of light reaching the bottom plants. So using the 110 watts and 55 gallons, you could say that at the bottom of this tank the lighting is 2 watts "per gallon", compared to the 3.5 watts per gallon at the top. So the light intensity at the bottom of this tank is a little more than 1/2 what it was at the top.
Please let me know if you need help with the calcs...It would be neat to have a bunch of folks do this and see what we all get. I don't know how to "post" a spreadsheet but if someone knows, let me know and I'll make one up so that people can just enter their numbers.