Watts per gallon out the window...

As I'm working on this compilation of how much light corals are being kept under successfully. I came to a realization of a much better (still not exact) way of measuring how much light a given tank needs. The problem came up when I realized I can't truly collect any data from different tanks because they are all different sizes.

My tank is 36" with one 250 MH above it. Of course someone could have that same MH sitting over a 24" tank dropping much more PAR on a smaller space.

The same goes for T5's. Longer bulbs obviously put out more wattage and more total PAR but over a more spread out space.

The conclusion I came to is watts/per linear foot of tank would be slightly more specific and would allow us to jump right to next (depth) step of finding coral that goes with our light.

 

Generally I think it's accepted that a MH bulb will cover a 2'X2' area. I agree watts per gallon doesn't really work.

 

It's possible that a MH BULB will cover 2' X 2' however the reflector can spread that light over a bigger area which drops the output to any one given spot under it.

That's really the problem I'm speaking of. My tank has a reflector that will spread 250watts over 36" while someone else may have a tank with reflector to spread that same 250watts over 24". That's a huge difference.

so if you run the numbers on that the 24" inch tank is getting 125 watts/per linear foot. The 36" tank is only getting 83 watts/per linear foot.

Now I would instantly see that the two tanks are not as comparable as they at first seemed and compensate by placing corals that work at a given depth in the 24" higher in the 36"

 

I agree with what your saying, but I think it's a little more complex then that. Have you ever noticed that even if you think your reflector covers a certain area, corals react differently when placed in different areas under the MH's. I believe it is safe to say that the further the coral is from the MH, the less PAR it will intake. This is a common problem with MH's. The light and lumen come from a single source or point. The PAR or lumens aren't spread out as evenly as you may think (even with the nicest reflectors).

I like the T-5 setups that are 6-8 or more lights running across the top. This gives an even distribution of lumen to all points in the tank. It would be more suited for the calculation you are talking about.

I don't believe in the watts/gal thing or anything like it. I believe in measuring PAR. Yes, it's too bad they aren't easily accessable to the average reefer, but average reefers don't think much about this subject either. And if you are going to spend hundreds, if not thousands of dollars on your reef, a $100-$200 PAR meter isn't that bad..

 

I think you run into the same issues with linear feet as you do wpg although to a somwhat lesser extent. Judging by linear feet you will probably get closer but it's still not perfect, especially with the really deep dimension tanks becoming more popular. A person with a 36" cube, 90g, is going to need drastically different lighting than a standard 30 gallon which is 36" wide by 12" deep.

I don't think there's a good way to simplify lighting honestly, it's a complicated situation with lots of variables.
To a certain extent I think simplifying complex subjects sometimes only causes problems, forcing people to learn at least a little bit about it so they can make a good decision is worth it to me.

Even though it's a little offputting having to learn about lighting, what ultimately is worse?
Simplifying the subject and having a certain percentage of newbies make bad choices which could potentially drive them out of the hobby when their tank fails or they realize they have to spend a lot more money to do what they initially wanted to do.
Or having a certain number of people never get into the hobby because they are intimidated by lighting or they don't want to put the time into learning about lighting etc.

I tend to lean toward making people learn about it, it's not a simple hobby and keeping successful tanks long term I think requires a good bit of knowledge, the more knowledge you have the easier it's going to be to not rely on dumb luck. Even with a decent amount of knowledge of the basics this hobby sometimes isn't easy!

 

Good point mike and i agree with you. Also mentioned above a par meter is great. I might have to buy one now.

 

I agree with what everyone is saying. Still not perfect. In the end there are just too many variables to truly calculate what a light will do on your tank. To be 100% accurate it has to be placed on your tank and the output has to be measured. I just think a revision of the watt/per gallon rule that you can still find in books published in the 80's is overdue. Watts per/square inch would be even closer still and that may be where I end up going with this. Even if I take it that far MH reflectors like chuckdee said are still going to throw things off.

Maybe I'm just reading too far into this.

 

No you not mike, watts per gallon is def out dated!

 

Watt's per gallon was'nt meant to be an actual statement to live by, but a minimum for coral tank's in general. Also depending on the type of coral's kept.
Ghost

 

Check with your local reef club. Ours has a PAR meter available for members to check out.