# How Rigid is the 1-2W per Gallon Rule?



## schaadrak (Aug 18, 2006)

I have a 12gal Eclipse that will be a NPT here shortly. It comes with 13W CF already in the hood and I was thinking of adding another 13W to it which would bring the WPG to about 2.17. Is that too much, or is there some flexibilty with the WPG rule?


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## onemyndseye (May 12, 2006)

Well... this is a loaded question ...

On the rigidity of the WPG rule:
the WPG rule tends to start breaking down the closer you get to 10G and below because there is a minimum amount of light needed to activate photosynthesis. For an extreme instance, if you took a 1G tank and put 5Watts of light over it effectively giving you 5WPG you would probably be very discouraged to find that nothing will grow in your 5WPG "high light" tank because a 5Watt light just doesnt pack the intensity needed to kick off photosynthesis.

WPG is a "Rule of Thumb" so to speak 

Now all that being said - 26Watts of CF's should be plenty for a NPT this size. 

Those Eclipse systems look so nice too 

Good Luck! 
-Justin
One Mynds Eye


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## schaadrak (Aug 18, 2006)

I figured there was more to it than just that.

Let the modifications begin!


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## iris600 (Feb 12, 2004)

*Ahh but in the case of tall tanks....*

I'm currently facing a lighting conundrum as well. I have a 35 gallon hex that is quite tall. I know that the taller the tank, the more light loss is experienced. I can either put 1 or 2 55watt 5500K bulbs over the tank.
Which decision is better for el natural knowing that my natural lighting, even near the best window in my apt, is minimal?


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## Peter66 (Aug 18, 2006)

To revive this one. Is there a specific reason why plants that do well in a normal tank with less than 1w/Gallon would not make it in a NPT?


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## Spidergrrrl (Oct 11, 2006)

I have somewhat of a vested interest in this thread too, as I just bought the same system (set it up this weekend!). 

I was researching how to retrofit the hood with additional lighting, but since I'm not very good at DIY projects, I got easily overwhelmed and intimidated. In the end, I decided just to see how things go with the default setup.

So, please keep us updated.


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## Zapins (Jul 28, 2004)

onemyndseye: very good explanation, I hadn't heard all of that in one place before. Seems like all one sees is glimpses of info that makes sense around the web, but nobody sums it up nicely like that.

Peter66: what onemyndseye was getting at was the fact that wattage (used in the watt per gallon rule) does not have much to do with how intense the light is. wattage is just a measure of how much electricity (in joules/second) is passing through a particular device (be it a stove, a fan, or a light) each second. Since wattage is just a measure of the power going through the device, it does not tell you how efficient the light is at turning that electricity into usable light. Thus, if you had a 60w incandescent light bulb and compared it with a t5 or power compact light of equal wattage, you would find that the 60w incandescent would not be able to grow plants very well, simply because most of the watts passing through the bulb are used to make heat - not light. The T5 and PC lighting are much more efficient at turning electricity into light and will therefore be brighter and throw off more light per watt than the incandescent bulb will.

For this reason, Peter66, it is possible that plants can do very well in a tank that has 1 wpg or even less. In fact, if you had a light bulb that somehow turned 90% of the wattage into light, and had equally good light spread, then you could adequately have a high light 125g with a very low wattage bulb (maybe ~30-45w). 

Because it will take many more low-intensity bulbs and much more $ via electrical costs to light a tank, people usually invest in quality lighting and reflectors and do not usually use lower efficiency bulbs like incandescent lights.

Also, in case you were wondering why people still refer to (and why it is still usable information to know) how much light they have in wpg terms, its because most people out there have higher efficiency lighting that have about the same light/watt output. For example T5’s and MH are pretty close together, even PCs are pretty close. So it makes less of a difference when talking about how much light we have, if all our light fixtures are all about the same intensity.


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## JeffLL (Oct 20, 2006)

*Florescent Rule*

Give or take, for each class (not size, configuration or pins) of _florescent_ lamp, such as standard, high output (HO) or *V*eryHO, the light per watt is comparable. It's also about output per size. The VHOs simply _use_ more electricity to make _more_ light, which may or may not be converted more efficiently. Age probably reduces output by much more than the difference between the the best and worst performers across ALL florescent offerings.

To sum it up, the rule of thumb is broad enough to say 1.5 - 2 Wpg of florescent lighting is the starting point. I am sure that there are plenty of people streaming in over 10Wpg.

Note that I will be using a GU10 or MR16 (low voltage) incandescent halogen track lighting mini spot lamp :flame: to warm a 'sunning' rock for my turtle(s) in my paludarium.

_______________________________________________
If you don't vote, you can't complain. Take your head out of your tank for half an hour and make a difference. The act and privelege of voting is what makes any democracy strong.


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## Peter66 (Aug 18, 2006)

Thanks for the reply, I use philips aquarelle with reflectors so I got suffiecient lighting for my plants in my current setup. Can I assume that my crypts and swordplant will not need more light simply because I change to soil under gravel?


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## ruki (Jul 4, 2006)

JeffLL said:


> Give or take, for each class (not size, configuration or pins) of _florescent_ lamp, such as standard, high output (HO) or *V*eryHO, the light per watt is comparable. It's also about output per size. The VHOs simply _use_ more electricity to make _more_ light, which may or may not be converted more efficiently.


Think your VHO information is dated. That was a true statement a while back, but from today's perspective VHO is an old, inefficient technology that requires significantly _more watts to get less light_ than the new choices that came out in the past decade. It's so 1980's 

You can get up to twice as many lumens per watt from the most efficient T5 bulb compared against the old T12 tubes. Between these are T5 HO, Power Compact, and 2x overdriven T8s.

Then you have reflector issues. PC tubes are folded, so they interfere with the reflector, so they aren't even close in light output sent down into the aquarium per watt when compared with a good T5 HO fixture.

It's one of those +/- 50% things. The watts per gallon rule is a convienient simplification when one doesn't want to think about all the above. It's also used by PC fixture vendors to gloss over the fact that using bent tubes for linear aquariums really doesn't make much sense now that T5 HO is here 

There are some incomplete charts demonstrating this: http://woo.gotdns.com/Aquarium/CalcLight.php?Width=18&Length=48
Luminous efficacy - Wikipedia, the free encyclopedia

Fortunately for us, most plants are highly adaptable. It doesn't really matter too much unless you have racks of tanks and want to reduce a quite large electricity bill.

You will do fine with many choices.

With global warming concerns and electricity prices likely rising in the future one can make an argument to use T5s or T8s in new fixtures.

This is my standard "watts per gallon" rant from the lighting forum


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## epicfish (Sep 11, 2006)

Minimum Light Threshold...or am I nuts? for why the WPG rule breaks down a small (<10 gallon) and large (~>100 gallon) tanks.


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## JeffLL (Oct 20, 2006)

*I Stand Corrected*

Ruki, thank you for disabusing me of the idea that VHO bulbs are as efficient as any other florescent ionizing light emitter.

Personally, I use El Cheapo T-8 technology. If I want more light I will add another 2x, 64W shop light for $42 including the bulbs and time them to 1-2-1 overlap sequence. In addition, this time there will be an incandescent spot light as a basking lamp/heat source.

As for the W/g, how do you think it applies in a paludarium? I run a 75g tank, where the total fill is 50g land and water, of which roughly 30g is actually water. 
_________________________________________________________________
A Jamaican who braids his spaghetti is a Pastafarian


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## ruki (Jul 4, 2006)

re: paladarium lighting

I beginning think the watts/lumens/PAR per gallon rule for aquariums breaks down for paladariums. I think the refraction property of the water/glass boundary keeps light inside the tank, so aquairum fixtures can be pretty sloppy as long as they get the light to hit the surface of the tank.

For example, I had a 15 tall with a 98 watt coralife fixture and the plants behaved as if they were light starved. I switched the tank over to an immersed sword tank and the plants were pearling without adding any CO2. This fixture works much better when water is in the tank.

Another example, on a whim, I picked up an outdoor fluorescent area light for $40.00. It's a mini version of the high bay fixture with a 65 watt PC bulb instead of a metal halide bulb. Regent: Product Detail for DL65FPC Series
I got some metalic spray paint too and painted the plastic reflector (only need to paint the exterior) and it worked better than expected in an 8 gallon hex paladarium. The bell shaped reflector sends much of the light straight down into the tank. The bulb claims to be 6500K. Replacement bulbs are around $10.00. For the money, it does a pretty good job considering that a good hydroponic reflector box costs around $100.00 and PC full spectrum bulbs run $50 - $150. You can find this at hardware stores such as Menards and Home Depot.

I'm still trying to figure out how to get this to work better. A taller reflector gets the light going straight down into the tank. Also, putting a sheet of mylar film on the back and sides of the tank helps much more than for a water filled tank.


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## schaadrak (Aug 18, 2006)

If I remember correctly the intensity of the bulb decreases exponentially as you get further away from it, meaning if there were 900 lumens/m² at 6in away from the bulb, then there would only be 30 lum/m² at 1 foot. Does that sound right?

So for a paludarium, you might need to calculate how much light is actually hitting the surface of the water based on how far away your bulb is. But also take into consideration that your water area is probably shallower than most other tanks, so the light won't have as much water to push through to get to the plants. So I'm going to guess maybe 3-4 WPG if your going to try and keep it El Natural?


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## dwalstad (Apr 14, 2006)

schaadrak said:


> I have a 12gal Eclipse that will be a NPT here shortly. It comes with 13W CF already in the hood and I was thinking of adding another 13W to it which would bring the WPG to about 2.17. Is that too much, or is there some flexibilty with the WPG rule?


There's lots of flexibility- plant species, window light, tank depth, reflector, etc. You didn't mention window light, which will dwarf most artificial lighting.

A regular 15 watt fluorescent bulb and reflector over a 10 gal tank works great, even without window light.

Therefore, I suspect that a 13W CF (provided it has a decent reflector) for a 12 gal would work fine.


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## schaadrak (Aug 18, 2006)

dwalstad said:


> There's lots of flexibility- plant species, window light, tank depth, reflector, etc. You didn't mention window light, which will dwarf most artificial lighting.
> 
> A regular 15 watt fluorescent bulb and reflector over a 10 gal tank works great, even without window light.
> 
> Therefore, I suspect that a 13W CF (provided it has a decent reflector) for a 12 gal would work fine.


Unfortunately, the tank is not near a window, is about six inches taller than a standard ten gallon and there is no reflector for the bulb. I might try it with only the stock light first, then upgrade if necessary.


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## ruki (Jul 4, 2006)

schaadrak said:


> If I remember correctly the intensity of the bulb decreases exponentially as you get further away from it, meaning if there were 900 lumens/m² at 6in away from the bulb, then there would only be 30 lum/m² at 1 foot. Does that sound right?


That's for a bulb radiating light in all directions without a reflector. I noticed that the "high bay" bell reflector worked much better than other ones to send light, through the air, to the bottom of the tank.

The goal is to have a really good reflector that creates a "light pipe" that gets light moving towards one parallel direction. Then the reduction is linear, based upon crud in the air. I haven't come really close to this for a paladrium yet


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## VirginiaIsoetes (Oct 27, 2006)

*Re: in the case of tall tanks*



iris600 said:


> I'm currently facing a lighting conundrum as well. I have a 35 gallon hex that is quite tall. I know that the taller the tank, the more light loss is experienced. I can either put 1 or 2 55watt 5500K bulbs over the tank.
> Which decision is better for el natural knowing that my natural lighting, even near the best window in my apt, is minimal?


Iris-

I have the same issue with my tall tank.

I started out my 35 gallon hex with one 55w 5500K bulb. That turned out to be insufficient. I ended up adding one 13w and then another 13w a month later. So far so good at about 2.3 w/gal.

I wish I had just installed two 55w initially and saved the trouble.

Cheers


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