How does shallow water depth affect par?

[LRT]

Just set my reefbreeders v2+ up using recommended settings for soft tank.
However I'm not in 24 cube as brs tested I'm in shallow water frag tables at reccomend height.
Is there a formula available to calculate par for shallow water reef systems?

 

[Reefer5640]

You could just use the same method they use for the cube but only use the measurements they give from the top down to the depth of your tank. The deeper the water, the more it filters the light. Or the further away from the light, the less par you will have

 

[jda]

Shallow water means less spread which means more intensity. Raise the light up if you want to emulate the BRS numbers.

 

[LRT]

I feel like your both kinda saying the same thing here.
@Reefer5640 are you saying take my measurement from bottom of lamp to top of corals?
I do have par meter coming from local club. Just trying to get close without burning things up before getting actual measurements.

 

[jda]

BTW - while air and water does filter the light, in our shallow tanks this is not the issue. I am not saying that it does not happen, just it does not really matter to us in quantities worth worrying about... so don't anybody get all academic on me and post a bunch of junk about water filtering a 30 meters or something when I get that it happens to a very small degree.

In our tanks, the lower PAR is from the spread when distancing from the source. When closer, more light hits the coral or PAR meter sensor - imagine being close and a light cone the size of a top of a can of Coca Cola. Then, when you move away and the light cone is the size of a frisbee or even farther the size of a lid to a 5 gallon bucket. The same light is in the Cola can that is in the bucket, just spread out more... so less intensity/PAR with the bucket lid.

Distance from the source is more important in our tanks than the filtering by air or water.

 

[Reefer5640]

Well I was assuming you didn’t have a par meter so you’d just base your rough measurements off the test they did in the vid. For example, if the cube is 24” deep and they took four different sets of measurements at different heights (6” below the water level, 12” below the water level, 18” below the water level, and 24” below the water level/bottom of the tank) then you’d only need to use the first sets of measurements to gauge your par (6” and 12”) assuming your frag tank is roughly 12” deep or less and frag rack sits around 6” below the water level then you’d have your par readings for your tank. The next two sets just don’t apply to you since you don’t have that depth to deal with. But if you adjust the height that your light is mounted to a different height than what they tested in the vid then you’ll have to do your own test all together. Which is a good idea anyways. Like @jda mentioned, the higher you raise your light the further out the light will spread and the spectrums will blend but you’ll loose par the higher you go. Not usually an issue with a Frag tank though. Renting/buying a par meter is definitely the way to go though. Think of holding a flashlight close to a wall and then stepping back. The spread gets more diffused and wider. Just the opposite the closer you get.

 

[Reefer5640]

I feel like your both kinda saying the same thing here.
@Reefer5640 are you saying take my measurement from bottom of lamp to top of corals?
I do have par meter coming from local club. Just trying to get close without burning things up before getting actual measurements.

But yes, that’s the reading you’d want to be targeting. I ya Sialkot raise the light just until it starts to spill over the endgame of the tank. Then adjust power of the light to target the par you’re after. There are other ways to go about this. That’s just what I do.