I have been waiting to make this post for a while now.
Waiting because I have long suspected that uniform light intensity is the real deal with lighting. The new apogee meter I got confirmed what I thought to be true.
Here is an example - you can have 100w over a tank and 400w of lights over a tank and have the same light levels in the middle of your tank. To achieve that, you would of course need to place the lights at different hights above the water.
However, with the 100w light that is close to the water you wont have the same light intensity throughout the tank - you will have alot of light at the top, and very little light at the bottom of the tank.
On the other hand, with a high output light mounted high above the tank, you will have much more uniform intensity.
Here is a real example - I have a newly set up cube tank that is 24" deep. I chose to go with a ceiling suspended MH light for a cleaner look. I could have gone with a 150w of light, which would give me good light levels with the light suspended 6"-8" from the water, however, this setup would create hot spots at the top of the tank, and much less light at the bottom - this would most likely lead to algae on the top leafs, especially if I wanted to place anubias or any low light plants at the top.
Instead, I went with a 250w light, suspended about 18" above the water, and this gives me an intensity of 100-110PAR at the top and 70-75" PAR at the substrate - this is alot better than the 140 on top and 40 at the bottom that I would have gotten with a 150w light.
These measurements were taken with an apogee PAR meter.
Some might say that this wastes alot of light - while this might be true, this is the only way to create a uniform intensity throughout the tank - think of it this way - the sun shines the same whether you are up on a mountain or bellow sea level because its a very big light source far away.
So when you consider buying new lights for your setup - consider buying a high output light but mount it higher up - you can even make a box around the light to prevent accessive light spill.
Waiting because I have long suspected that uniform light intensity is the real deal with lighting. The new apogee meter I got confirmed what I thought to be true.
Here is an example - you can have 100w over a tank and 400w of lights over a tank and have the same light levels in the middle of your tank. To achieve that, you would of course need to place the lights at different hights above the water.
However, with the 100w light that is close to the water you wont have the same light intensity throughout the tank - you will have alot of light at the top, and very little light at the bottom of the tank.
On the other hand, with a high output light mounted high above the tank, you will have much more uniform intensity.
Here is a real example - I have a newly set up cube tank that is 24" deep. I chose to go with a ceiling suspended MH light for a cleaner look. I could have gone with a 150w of light, which would give me good light levels with the light suspended 6"-8" from the water, however, this setup would create hot spots at the top of the tank, and much less light at the bottom - this would most likely lead to algae on the top leafs, especially if I wanted to place anubias or any low light plants at the top.
Instead, I went with a 250w light, suspended about 18" above the water, and this gives me an intensity of 100-110PAR at the top and 70-75" PAR at the substrate - this is alot better than the 140 on top and 40 at the bottom that I would have gotten with a 150w light.
These measurements were taken with an apogee PAR meter.
Some might say that this wastes alot of light - while this might be true, this is the only way to create a uniform intensity throughout the tank - think of it this way - the sun shines the same whether you are up on a mountain or bellow sea level because its a very big light source far away.
So when you consider buying new lights for your setup - consider buying a high output light but mount it higher up - you can even make a box around the light to prevent accessive light spill.
on this subject. Air and water have what is called an index of refraction. I won’t go into what that means but needless to say when light passes from one index of refraction into another if the two indexes are of different values the light gets "bent" and does not travel nicely between the two mediums. However this issue is easily solved by directing the light normal (90degrees) to the surface. When the light strikes the surface normal it has a much better chance of penetrating straight through. Thus when we place the HQI much further from the tank we see a much better penetration vs the PC light that is much closer and directing a lot more light not normal to the surface. If you ever want to experiment with this try taking a CF fixture and do a water change. Notice when the water is low the places furthest away from the light seem to be getting a lot of light. Well, refill the tank and simply look at the same spots.... Much less light....Ahhh... you have found the many wonders of the index of refraction. In equation form it is Tan(theta1)/Tan(theta2)=index1/index2. The index can also be seen when you try and pear down into the water from above the tank, it’s not easy to see inside. However glass and water have a better index ratio and you are looking normal you are easily able to see into the water.
