2 watt/gal. rule VS. aquarium light efficiency

  • We are currently upgrading MFK. thanks! -neo
M

m1ste2tea

Jack Dempsey
MFK Member
Nov 17, 2009
1,086
1
38
Syracuse, NY
Hello all, I have searched for this topic on a number of forums and would like to ask you all on what you think of these questions...

(these question are involved with my knowledge or lack their of about how light interacts with water, and how watts interact with an aquarium and its contents.)

QUESTION 1) The "2 watts per gallon" rule for planted tanks... is it something that I can cheat my way around by setting up a more efficient tank?



QUESTION 2) since darker objects absorb light and light colored objects reflect light, and since putting in things such as white sand and a mirror background will brighten up the tank considerably, will such things help the plants grow?

QUESTION 3) Is it the the watts, lumens or the lux, etc etc that is the primary drive of photosynthesis for plants, and a high reflective tank as mentioned above improve the plant's absorbtion of it?

QUESTION 4) Is it really a matter of volume(gallons) or depth(height in/cm) that determines how much light gets to the plant? For example: is 10 gallons/5 inches high better than 10 gallons/10inches high?
 
post in the planted section should have more luck
 
Posted by Wyldfy in the planted stickes


By: ErrorS at www.AquariaCentral.com

I want to get rid of watts per gallon, I'm sick of it. It just plain doesn't work anymore.. MHs can be anywhere from 70 to 110 lumens per watt, incandescents and halogens can be from 10-20lumens per watt and Fluorescents (HO, VHO, NO) can be anywhere from 45 to 130 lumens per watt. That's a huge range.. just in commonly used bulbs for aquariums you can go from 70 to 130 lumens per watt.

It's horrible.. I could tell you I had 6WPG of VHOs on my tank, which sounds really really high, but it's only outputting the light of 3WPG of normal output fluorescents.

It's simple enough..

just lumens divided tank (depth*2) + tank width + tank length. It's very simple, based on lumens per gallon except it stresses the tank height more.

In other words.. you multiply the depth times two, then you add this number to the width and length and divide the lumens with it.

So for 10K lumen output on a 55G tank it would be: 21*2 (42).. 42+12+48 (which would be 102), then you divide 10,000 by 102 to get the value you need.

Below 50 is very low lighting - (fish only)
50-150 is low to moderate lighting - (Fish only or lower-light plants)
150-250 is moderate to high lighting - (typical planted tanks without CO2)
250-350 is high to very high lighting - (Good reef tanks or heavily planted)
350-450 is very high to extreme lighting - (the best reef tanks or extremely high light plants)

This is for 10k Lumens, about two 55W power compacts.

72x25x25 - 180G-(tank is 147) - 68
48x24x21 - 75G - (tank is 114) - 87
48x12x21 - 55G - (tank is 102) - 98
30x12x30 - 46G - (tank is 102) - 98
30x12x12 - 20G - (tank is 066) - 155
30x12x18 - 29G - (tank is 078) - 128

As you can see, the 46G, even though it has less volume requires just as much lighting as a 55G.

Now, if it was 20k lumens which is a good value for a 55/75 moderately planted aquarium (This is about two 175W MHs average.. or a bit less than four T5 HOs), you wuold have these numbers.

20K lumens is about what people seem to shoot for in a 20L reef and you can just get by with this amount in a 29G reef.

72x25x25 - 180G-(tank is 147) - 136
48x24x21 - 75G - (tank is 114) - 175
48x12x21 - 55G - (tank is 102) - 196
30x12x30 - 46G - (tank is 102) - 196
30x12x12 - 20G - (tank is 066) - 303
30x12x18 - 29G - (tank is 078) - 256

Most bulbs vary only a small amount in lumen output.. even full spectrum bulbs, for the 5000-6000lumen bulbs (T5 HOs) it's only a matter of 500 or so lumens lost to get some of the invisible spectrums for your plants, which doesn't mess up the values above..

or the equivilent of one 48'' bulb or one of those 40W screw-in CF bulbs, about 3000 lumens.

72x25x25 - 180G-(tank is 147) - 20
48x24x21 - 75G - (tank is 114) - 26
48x12x21 - 55G - (tank is 102) - 29
30x12x30 - 46G - (tank is 102) - 29
30x12x18 - 29G - (tank is 078) - 38
30x12x12 - 20G - (tank is 066) - 45
24x12x12 - 10G - (tank is 060) - 50.. and as you know, one screw in CF is about enough for low light plants in a 10G, most people fit two, which would simply double this number making it 100...
 
m1ste2tea;3634091; said:
Hello all, I have searched for this topic on a number of forums and would like to ask you all on what you think of these questions...

(these question are involved with my knowledge or lack their of about how light interacts with water, and how watts interact with an aquarium and its contents.)

QUESTION 1) The "2 watts per gallon" rule for planted tanks... is it something that I can cheat my way around by setting up a more efficient tank?
yes if you use led, otherwise the 2 watt per gallon is valid(enough that it works) for all other aquarium lighting


QUESTION 2) since darker objects absorb light and light colored objects reflect light, and since putting in things such as white sand and a mirror background will brighten up the tank considerably, will such things help the plants grow?
it wont make that much of a different.

QUESTION 3) Is it the the watts, lumens or the lux, etc etc that is the primary drive of photosynthesis for plants, and a high reflective tank as mentioned above improve the plant's absorbtion of it?
use ppfd or par, that measures the amount of light put out thats usable by photosynthesis.
watts is energy used by light to power them, lumens is amount of light put out, lux is lumens put out over a certain area.
you can have all the lumens you want if its not the right wavelength, you may as well not have a light at all.
QUESTION 4) Is it really a matter of volume(gallons) or depth(height in/cm) that determines how much light gets to the plant? For example: is 10 gallons/5 inches high better than 10 gallons/10inches high?
Click to expand...
its depth and width that matters.
 
thank you, That helps a lot, with this information I find out that my 55gallon planted tank is supremely under-lit. with only 870 lumens and 16 inches of water.

I currently have only 3 - 15watt fluorescent bulbs producing 290 lumens each... I have an unused 48 inch light hood but do not have the fluorescent bulbs for it. If I have lets say a $50 budget for lighting, should I buy 2 bulbs for that 48" hood somewhere like home depot or should I invest in another, more efficient light system with more lumens per watt?

okay... last question, mostly concerning Syndicate's reply: if the water depth is that significant, does it matter how high the plant sits in the water? lets say I put a plant up on a rock halfway up in the water rather than on the same rock on the bottom of the tank... would that help it grow?
 
If you are looking for lights under 50 try aquariumtraders.com. They have reasonable lights for that price. A Power compact would do.
If you want to through home depot route you can buy 2 basic shop lights have 4 full spectrum normal flourescent bulbs and you should be set.
If you want to retro fit then you could try ahsupply PC light - it has good reflector and 1 of those should be ok if push comes to shove.

I have personally done the shop light version and it was good plant growth- only not aesthetically pleasing and always the worry of water hitting the bulbs.
If you want good looking lights try fishneedit.com
The new kid on the block which might work is SHO pc lights at americanaquariumproducts.com. It fits into regular screw type bulb fixture and puts out huge amount of light- might be too much for you.
 
You must log in or register to reply here.
MonsterFishKeepers.com
Top Bottom