# WPG no more?



## Moo (Apr 27, 2006)

In my quest to determine the best lighting solution for my 58 gallon lowER tech crypt, anubias (low light) planted tank.
I've found a few different interesting points/ideas.
hahah just when I thought I had the fixture I wanted.

okey dokey I'm sure most of you are famaliar with Rex Grigg?
well on this page he talks about not WPG but luxeons and all this other slightly not so odd things. I've also seen similiar suggestions else where.
One instance I believe on this forum.
The idea that wpg doesn't work...alteast very accurately.



> Rex Grigg:
> Now I know what you are thinking. I can do watts per gallon pretty easy. But how do I figure this LSI thing? Well find the surface area of your tank in square inches. Then take the LSI number you want to reach. Multiply the surface area by the LSI. Take the result and divide it by the LUX rating of your chosen light. I will admit that this system is not perfect by any means. But I think it gives a better idea than the WPG rule.


So I did this
36.5*18.5=675.25
LSI#=17
675.25*17=11479.25
11479.25/?

The LUX rating. I have yet to see any lighting system rated by LUX...even if I had.
Why can't I just say that 96 watts of light over my 58 gallon tank will get me
1.65 WPG? Is it the same?
If I knew the LUX rating of the 96 watts would the LSi be that much different.

If anyone know how to get the LSI that would be great I'm interested to see what the answer is, but if not just tell me if I really even need this? or my original 96 watts will be just fine.

-matt


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## erik Loza (Feb 6, 2006)

Are you designing the next space shuttle or just trying to get some lights for your next tank? Seriously, step back and look at this formula you're working out. Do Anubias and Cryptocoryne do math? I'm busting your chops, of course, but why does it need to be so complicated? I have Anubias frazeri thriving in a tank with <1 wpg of diffuse PC light and I have Anubias nana and Cryptocoryne wendtii thriving in the shady portions of my big tank, which has 4 wpg of intense and direct MH light. These are plants, not hospital patients, and I am always surprised by their flexibility and resiliency. 

Just ballpark the lighting you think you need, then get a fixture that fits your aesthetics and budget. You said "quest", but why? It's a fish tank, just like the rest of ours. Set it up, enjoy it, let the plants and fish do their things, and share pics. Get it going, dude!


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## Laith (Sep 4, 2004)

And Rex is talking about tanks outside of the 20-75g range where the usual wpg rule of thumb applies differently...


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## PeteInEssex (Jul 29, 2006)

I was also spending some time on Rex's lighting page last night.
It is true that lux will give a more valid result than wpg, however, the amount of lux striking the top of the tank water will be much greater that the lux that makes it to the bottom of the tank.

For each 12" of distance between the light source the object being illuminated the amount of light falls dramatically (in an expotential fashion), so wpg may give a rough idea of light required, but measuring lux will be more accurate. 
As far as I remember, if there's say 24,000 lux at 12" from the light source there will only be 6,000 lux at 24" and 2,667 lux at 36" (that's in air, not sure about water). But as erik said above we're not talking about a matter of life or death here.

The reason the wpg is more of a guide than an exact science - 
If I have 10 gallons of water and I put it in a 'tank' with a light over it, the dimensions of the tank will dictate how much of that light reaches the bottom of the tank.
If the 10 gallon 'tank' is only 2" deep, the bottom of the tank directly under the light will get a lot of lux, then horizontally further from the light the bottom will get very few lumens. If the 10 gallon tank is 4"x4"x48" deep (purely hypothetical of course) then very few lumens will reach the bottom.
I guess wpg works most of the time as there aren't that many people who have tanks 2" deep or 4"x4"x48" !!

As there was nothing worth watching on telly last night, and I had been wondering about a better way of working out lighting requirements than wpg so I played around with the figures.

Re-working the math that Rex uses for a high-light tank (30 lux per sq.") 
71Wats delivers 60,000 lux
therefore
1W delivers 84.5 lux

For my purposes, my tank has a surface area of 54" x 18" = 972 square"
972" x 30 lux = 29,160
so I need to provide about 29,160 lux
so, 29,160 / 84.5 = 345 watts total light required for a high-light tank with a surface area of 972 sq."

This calculation still doesn't take into account the tank depth. Maybe one day I'll dig out the book I used to use for lux/lumens etc and see if I can refine the results, but I'd have to get very bored before I do that.... 

I've no idea if this is really a valid way of working things out, but I have a total of 400W over the tank (54x18x24) and in combination with pressurised CO2 and Tom Barr's EI dosing method the plants are growing at a scary rate - and the fish all have a nice tan 

Good luck
Pete


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## PeteInEssex (Jul 29, 2006)

As an aside, using google I found that the Iwasaki MTD150D Metal Halide 6,500K lights I'm using provide 11,000 lux.
The Triton flourescent tubes provide 2000 lux.
I have 2 x MH lights and 3 x Triton tubes, so I've got 28,000 lux.

So I'm in the right ball-park..

Pete


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## hoppycalif (Apr 7, 2005)

When you buy a new fish tank, it may come with an aquarium light. So, the question we all face in that circumstance is, is that light good enough to grow plants? The watts per gallon "rule" lets us answer the question, and the fact that the answer is almost always "no" isn't the point. Now, we have to decide what lighting is good enough to grow plants. Rather than go thru some big equations and do a lot of research, we can just double the gallons the tank holds and look for lights with that many watts or more and good reflectors, and we are in business. As pointed out above we aren't designing a space station, or even a tool shed. Plants are not very demanding of perfection. We just need to be in the right ballpark.


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## PeteInEssex (Jul 29, 2006)

There's an in-depth article here - 
http://www.aquabotanic.com/lightcompare.htm

I lost interest after the first paragraph though..

Pete


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## Moo (Apr 27, 2006)

haha yeah "quest" I don't mean to make it seem like a hassle otherwise I wouldn't be doing it. :: shrugs :: That's just the word I used. lol

I agree though. I mean if I were doing an incredibly hightech tank then mabey I would use that formula.

Mabey I just don't get why people try to make moluecular physics out of the aquaria hobby.
I guess you just use what works, but wow. That seems like an obsured amount of effort for fish?

haha I like the way you put it erik. 
And no, actaully in my "freetime" (that is when I'm not doing school/job/fish/computer training I design high-powered small scale model rockets. lol)
But believe me if I did have the money to design a Space Shuttle I wouldn't be designing one. I would design a ridiclously and unessecary monstrous aquarium. hahah.

Thanks to all for your replies.
-matthew


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## czado (May 26, 2005)

double post


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## czado (May 26, 2005)

It is important to remember that the realistic goal of these new lighting standards is a better guess. 


PeteInEssex said:


> Re-working the math that Rex uses for a high-light tank (30 lux per sq.")
> 71Wats delivers 60,000 lux
> therefore
> 1W delivers 84.5 lux
> ...


 But, say, 71watt CF has more lux than 71watt T12. Lux is derived from lumens, and lux/square inches is really lumens/square meter/square inch. Just something to think about.

Here's Wizzard~Of~Ozz's lighting page and ideas for your consideration, well written and understandable. It differs from the idea above by also attempting to account for bulb efficiency and sample real tanks. I have lots of links and calcs and stuff if you want them or to contribute your ideas.

For our purposes (a better guess), especially with Moo's 18" tall tank, I don't think accounting loss from light penetration into water is so important. When people shared how much light would be needed for specific carpeting plants, most of them were trying on tall tanks anyway.

Moo,

Assuming the 96w is CF, the linked article/standard would say you'll have a little more medium light, and would call it more like 2.3wpg than 1.9wpg. In the end your original 96w will be fine, but you maybe increasing light by more than you think. CFs are great.


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## Moo (Apr 27, 2006)

You said 18" tall. I guess I left out what that last dimension is....or if it really even matter's. It's and oceanic 58 gal. so it's 36.5x18.5x21
It's only three inches difference But I figured everyone might as well know. lol
sorry.

Thanks for all the info czado, godd stuff on that page. Now I know more of what Rex was getting at. :: shrugs :: I'll proabably tank into account that 96 watts may be a little higher than what I wanted to begin with, but I'm not bending over backwards to find lighting that fits exactly in a range. anywhere between 96 and about 70 is fine with me. lol

thanks again guys.
-moo


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## Moo (Apr 27, 2006)

Since I'm looking around, I found this 
2 x 36 watt Bright Kit Item # 30362 
at
ahsupply
http://www.ahsupply.com/36-55w.htm
it says it's only 34.5 inches long...will that create dark spots on the ends of the tank?
The reason I'm doing this one and not the 96 watt kit is for the lower wattage, but I still may end up doing the 96. I'm just getting ideas right now.


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## Moo (Apr 27, 2006)

:bump:
would that ^^^ be alright? or do you think I should just stick with 96 watts.


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## hoppycalif (Apr 7, 2005)

For a 58 gallon tank I wouldn't use less than 96 watts. It is just a little shorter than the tank length, so it shouldn't leave any noticeable dark areas at the ends. This would leave you with a low to moderate light intensity, and if you later want more light you can get a second kit or the 2 x 36 watt unit.


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## ruki (Jul 4, 2006)

*quick summary on lighting choices*
I tend to think along these lines when I'm too lazy to think about PAR when comparing fixtures:
* What kind of technology (T12, T8, T8 overdriven, T5, T5 HO, PC, metal halide, ... )
* How great a reflector
* What sort of tube (5000K, 6500K, Grow Lux, specific aquarium bulb)
Then coupling the above with how this has worked for others. This place is a gold mine for such information.

The above post gave experience on needing at least 96 watts for 58 gallons in the earlier context of using aquarium PC plant tubes with those decent AHS refectors.

*watts per gallon is not a rule*
WPG is just a very rough estimate, people shouldn't be using it as a rule. With all the different lighting choices and reflectors, the error/estimate may be as large as +/- 80 percent, especially when you consider PAR (Photosynthetic Active Radiation -- light that plants actually use to grow) and reflector efficiency. Other measures Lux and especially lumens are human focused which doesn't relate very well to our submerged green friends.

One of my pet peaves is that we tend not to use error bounds. That makes people think it's a rule and not an estimate. Without error bounds, one has no clue as to how useful it is. Some aquarium writers either have poor science backgrounds or are intentionally dumbing it down because their audience prefers absolutes over useful models of reality. Too many times, I've seen newbie DIY people get innappropriate tubes for their plants since any concept of PAR was omitted from an article on aquarium plant lighting. "Well, I have 80 watts of light, but". As you can probably guess, this irritates me to no end!   

In case there are doubters on +/- 80 percent... You get an immediate 20 percent on Normal Output (NO) fluorescent tubes if you use T8's instead of T12's. Same light for 20 percent less watts. Reflectors can double the light actually sent down into the tank. PAR values for tubes differ much more than one would suspect http://www.aquabotanic.com/lightcompare.htm has some tube comparisons. At least another +/- 40 percent here.


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## Moo (Apr 27, 2006)

as said above I will probably be using the AH supply fixtures which are supposed to have excellent reflectors.
thanks for your replies guys!
-moo


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