<1wpg plants?

[aquabillpers]

Hi,

A 30 inch deep tank requires only 3.3 percent more lighting
"intensity" than a 12 inch deep tank? That is very counter-intuitive. Can you supply a reference?

I think that WPG is of value only because it is easily calculated. A better number would be lux measured at the bottom of the aquarium. Lumens is a measurement of light energy emitted by a source; lux measures light received and varies with the square of the distance from the source. See
http://www.aquabotanic.com/lightcompare.htm#S-2.

I have always had trouble growing plants like vallisneria in a 2 wpg low tech 16 inch tank. The same species grows like the weed that it is in a 2 wpg 10 inch tank.

Good luck!

Bill

 

[Captain Hook]

The actual 3.3% might not be right but this guy knows his stuff and I think what he is saying about light and depth is correct. I have read this in other places but can't remember where right now.

Interesting Read (Complicated!!!) on Light & Water Depth

 

[aquabillpers]

Ten feet away from me is a 20 gallon tank that is about 10 inches deep, considering the substrate. It is lit by 40 watts of GE Chroma 50 T12's. It is only a few weeks old but the plants seem to be off to a good start. It looks bright to me.

But if I raise the lighting fixtures by a foot the tank becomes noticeably dimmer, so much so that I would be surprised if much grew in it. Anybody seeing the two would immediately see a big difference. And air absorbs less light energy than water. Try that experiment.

I suspect that much of the illumination loss comes from the fact that the light spreads out - there is a fixed amount of lumens spread over a larger area. To compensate for that, the amount of light would have to be increased. So it would seem that the further the light source is from the place where it is needed, the more wattage is required.

Bill

 

[freq43]

intensity vs depth

Hi Bill..

This would be true if your aquarium did not have glass walls. Up to a certain depth the walls reflect the light back into the tank, keeping it inside and helping it penetrate deeper. The same concept is used in fibre optic cables.

Some very interesting reading from the krib:

http://www.thekrib.com/Lights/depth.html

Cheers
Andre

 

[aquabillpers]

Thank you, Andre.

I'm sure that there is some light reflected back from the sides of the aquarium, but some is also lost. Witness the light on the floor from a tank in a dark room at night. And i can read in the escaped light from my 29. Algae and biofilm will also absorb some light.

The krib? I read some of the articles and here are some selections:

"Executive summary: Light intensity from a dual 40w shoplight
is inversely proportional to the distance from the bulb. "

http://www.thekrib.com/Lights/depth.html#6

A measurement with a light meter that supported the "intensity
decreases with depth" theory (if I read it right)

http://www.thekrib.com/Lights/depth.html#0

There are other articles there that seem to support both views. One key point that was made several times is that unless the water is perfectly clear and there are no intervening objects like plant leaves and suspended stuff, some light energy will be absorbed before it reaches the bottom of the tank. It would seem that there would be more such interference in deeper tanks than in shallower ones, so . . .

Bill

 

[plantbrain]

For a 55 gal, why not use a cheap shop light or make a simple nice looking wood box and have 1.67 w/gal?

This will grow about 95% of aquatic plants folks normally keep.
Add CO2 and then you have an easy to deal with tank that has good plant growth and very little nutrient issues.

Seems easier than trying to squeeze out some light from over driving a bulb and a better long term solution.

I've used this set up and have grown most plants and had very nice success with foreground type plants. Gloss, Hairgrass etc

Regards,
Tom Barr

 

[ChicoRaton]

plantbrain-- in response to your "why not...", My way is free maybe when I sell my computer monitor I'll have enough cash to get two shop lights and a glass tank cover. That'd give me 160 watts so just about 3wpg, and I'd hook up some diy co2. Until then, though, I think I'll start planting with the above mentioned plants that can cope with low light and then wait. Thanks for all your ideas!

 

[freq43]

Originally posted by aquabillpers

There are other articles there that seem to support both views. One key point that was made several times is that unless the water is perfectly clear and there are no intervening objects like plant leaves and suspended stuff, some light energy will be absorbed before it reaches the bottom of the tank. It would seem that there would be more such interference in deeper tanks than in shallower ones, so . . .

Bill [/B]

Hi Bill

I agree with you, some intensity will be lost the deeper the tank is, I was just trying to highlight that it is not as much as the inverse square law dictates.
I think that the shape etc of your tank also makes a big difference on this subject.