The Planted Tank Forum banner

1 - 5 of 5 Posts

·
Premium Member
Joined
·
4,840 Posts
Discussion Starter · #1 ·
I have 108 watts over my 29 gallon. They were sitting right on top of my tank until today, I finally decided to hang them. 108 watts was just a bit too much, most of the time it was fine but a big trim led to algae quick. I was wondering if it is at all possible to guess where I am at now, just for curiosity. I can't see myself going out to buy a par meter just for curiousity sake.
 

·
Registered
Joined
·
21,012 Posts
The intensity drops with the square of the distance between the light and the point where you want to know the intensity. So, if you want half the intensity at the substrate, raise the light so the distance between it and the substrate increases to the square root of 2 times what it was, or 1.41 times what it was. If it started at 20 inches, you would raise it to 28.2 inches.
 

·
Registered
Joined
·
13,609 Posts
I have 108 watts over my 29 gallon. They were sitting right on top of my tank until today, I finally decided to hang them. 108 watts was just a bit too much, most of the time it was fine but a big trim led to algae quick. I was wondering if it is at all possible to guess where I am at now, just for curiosity. I can't see myself going out to buy a par meter just for curiousity sake.
Errr, why do you need to buy a meter when the plant club locally has one?

Regards,
Tom Barr
 

·
Premium Member
Joined
·
4,840 Posts
Discussion Starter · #4 ·
Errr, why do you need to buy a meter when the plant club locally has one?

Regards,
Tom Barr
Between work, girlfriend, music making, restoring a car, I don't have time to join one, though I think I should when I get more time to myself.


Hoppy, I just kind of assumed light doesn't travel through water as intensely as air. I don't know if that is true but with my one college physics course, I know light refracts though water (right terminology?) so I figured you would have less of a drop raising your lights off the tank, than having a deeper tank. Again, an assumption, probably am wrong.
 

·
Registered
Joined
·
21,012 Posts
Between work, girlfriend, music making, restoring a car, I don't have time to join one, though I think I should when I get more time to myself.


Hoppy, I just kind of assumed light doesn't travel through water as intensely as air. I don't know if that is true but with my one college physics course, I know light refracts though water (right terminology?) so I figured you would have less of a drop raising your lights off the tank, than having a deeper tank. Again, an assumption, probably am wrong.
I assumed the same thing, but when I tested some lights to verify that, I found that there is little difference between raising the light into the air and making the tank deeper to increase the distance. Very little light is lost due to absorption by water, over the distances we see with aquariums. And, the refraction helps to concentrate the light more, not reduce it. I have never been interested in knowing the light intensity within 10% accuracy anyway. My interest is more in the range of 25% accuracy. If I were doing a serious experiment in a lab, the higher accuracy would be of great interest, and I would need to actually measure the light and how it varied across the area being lighted, using a well calibrated light meter. But, for our use, that is very much overkill.
 
1 - 5 of 5 Posts
Top