# has there been a change in the WPG rule?



## kyle3 (Mar 22, 2006)

I was told on another forum that my lighting which i had described as medium was actually high accoring to the "updated wpg rule"

i have 36 watts of t-5 over a 20 long

i haven't heard anything about this change to the rule and i'm wondering if any of you have. Do you know where i might read more about it?

thanks for your input!
cheers-Kyle


----------



## turbomkt (Mar 31, 2004)

They are probably trying to say the T-5 is more efficient so you have more light than the straight ratio.

I'd still treat it as a medium light tank at best.


----------



## AaronT (Apr 26, 2004)

Watts per gallon is a terrible rule in general. Lumens are a better measure of light intensity. T5 bulbs put out more lumens for less wattage. That is why someone told you your tank has more light than you might have thought. I would say you can probably grow most anything in that light, but you may have issues with light spread because the T5 bulb is so skinny.


----------



## kyle3 (Mar 22, 2006)

AronT: "you may have issues with light spread because the T5 bulb is so skinny."

yeah, the rotala in the back definately leans for the center and my microsword in the foreground needs some help- i've only had this light for 2 months and i've noticed that

as far as lumens go i've read they're not an ideal measure either b/c the measurement is oriented towards light spectrums the human eye can see and have little to do with what a plant can absorb

but i can definately tell their a heck of a lot brighter than my old t-8 florecents b/c the plants are showing more growth and the red ones are more red.

i also think it gives me a little more light absorbtion having such a short tank: it's about 10 inches from the surface to the gravel.

anyway she was certain she'd read somewhere that the rule/guideline had been changed

thanks for the responses!


----------



## Lauren (Mar 18, 2006)

I don't think it's been changed, I just think more people are realising that, like every rule, there are exceptions. "rule of thumbs" tend to be very lose generalizations that have loop holes. For example, you can get away with a lot less light on a small or shallow aquarium vs. a deep or large aquarium. That, on top of all of the different lights there are up there, ads a lot of complexity to a very general rule.


----------



## SnakeIce (May 9, 2005)

This is not my experience but what I have gathered. The wpg was based on t12 lighting and even when considering that the next popular size, t8, is roughly 1.5x more effective per watt the differences in the amount of light most usable by plants put out by various bulbs ment that the old wpg was still reasonable.

Now, t5HO comes along, especially with new materials used in parabolic reflectors and the old wpg isn't quite as applicable. HOt5s with reflectors can put out 4x as much light per watt than the t12s put out.

The other side of the coin is that fertilizeing techniques and better CO2 distribution methods have made very high light more managable.


----------



## DelawareJim (Nov 15, 2005)

Lauren's right about rule's of thumb.

I've got 4 WPG using 2 175W MH and 2 40W T-12's on a 30" deep tank. I've got poor light penetration because of the depth. When I've asked if anyone has had good results from brighter lights, I get flooded with replies saying I've got a high light tank and I don't need any more light. Meanwhile my red plants loose their color, and my foregrounds fade away from lack of light.

Cheers.
Jim


----------



## turbomkt (Mar 31, 2004)

Jim,
I know what you're talking about. I've got 182 watts over a 50g corner tank. At 24 inches deep, it can get pretty dark toward the bottom. But up toward the middle of the tank things go crazy.


----------



## Raul-7 (Feb 4, 2004)

I have the same Coralife fixture over my 20-long; with 1.8w/g I thought I would be limited to low light plants but I'm happily growing P. stellata 'BL', Blyxa japonica and Cyperus helferi without any problems - infact the stellata is a nice magenta color. But remember this tank is rather shallow compared to more common sizes.

I believe the w/g rule is directed more towards NO T-12's or T-8's, not mention you have to take depth into account. I think intensity is more accurate.


----------



## carpguy (Feb 3, 2006)

*Never did like that rule&#8230;*

The argument against lumens is that they're a measure of how we see the light and not of how the plants use the light. And that's sort of kind of true, but turning around and setting our thumbs on watts doesn't address that objection&#8230; watts are just a measure of the energy going in, not of the light coming out. And definitely not of where it goes next.

My impression is likewise that the original rule was for T12s. T12s give off something along the lines of 65 lumens per watt. T8s and T5s are closer to 95 lumens per watt. Metal Halide is similar, maybe a little bit higher. That gives me either 3.2 CF wpg shining down on my 30g or the equivalent of 4.7 wpg T12. And that's before bulb shape, ballast, reflector, depth of water, etc.

There are other elements to consider, but lumens to lumens is a comparison, watts to watts is too often apples to oranges.

I never did like that rule&#8230;


----------



## zoogan (Sep 15, 2005)

Hi All
I like plant speak rules 
1. plants moving towards light/ uneven light coverage
2. plants stretching towards the light/ not enough light
3. plants with poor colour/ poor or wrong colour temperature globes
strange as it may sound plants speak through there leaves and habit.
Rules are only good to a point and every rule has an exception. Don't follow rules blindly look at your plants and then decide if you need more or less light. Nutrient deficiencies are another thing (the signs are the same as land plants).
Bye zoogan


----------



## czado (May 26, 2005)

Here's my Excel/O spreadsheet that uses lumens/watt from Ivo Busko's samples in his article on aquabotanic (and manufacturer specs for T5 and T5HO) and some quick and dirty deviation to give "equiv T12 wpg" and more importantly the better metric "lumens/sq in." (linked article's author, Wizzard~Of~Ozz, also has all calcs and ommitted bulbs at the end.) Here's Wizzard`Of~Ozz's online database, which some folks use to collect samples of real-life tanks to come up with new lighting levels -- your experiences are surely appreciated. While lumens/sq in isn't perfect, it does appear to hold up much better than wpg, especially across tanks of different sizes.

Here are my calcs for equiv T12 watts. T5, T5HO, and MH have very small sample sizes. These are also in the bulbs book of the above .xls file. Apologies if the format only looks good on my screen 

```
bulb   Lumens/watt    Eq T12 watts
T12    58.9            1
T10    62.3            1.06
T8     91.1            1.55
T5    104              1.77
T5HO   92.6            1.57
MH     84.1            1.43
CF     79.4            1.35
```
 Happy to provide the sample data. There is good discussion about this off-site here.

Hope this helps.


----------



## hoppycalif (Apr 7, 2005)

Intuition says that a bulb in a reflector that redirects most of the light from the back and sides of the bulb so it enters the water is more effective per watt than one with just a flat reflective surface behind the bulb. Does anyone know what that ratio is?

When the 2 watts per gallon "rule" started, people were mostly using T12 bulbs with flat reflectors behind them. So, using that chart above, I would say using T8 bulbs instead would increase the lighting by 1.55, except that T8 bulbs are lower wattage for the same size. So, for 24" long bulbs, the reduction is from 20 watts to 17 watts, or .85, making the T8 increase only 1.55 * .85 = 1.31, still a big improvement. But, does that mean the 2 watts per gallon "rule" should be 2/1.31=1.52 watts per gallon?

Now, if I use an AH Supply reflector, how much better is the T8 bulb? And, is that the main reason for the effectiveness of AH Supply's reflector/bulb kit?


----------



## BryceM (Nov 6, 2005)

I really like this thread because it's making me laugh. The notion that there is a "rule" is ridiculous. I think most people are looking at creating a nice looking tank. To that end, some discussion of light intensity is important, but there isn't a WPG rule any more than there is an inch/gallon stocking rule.

What matters to the plants is the amount of light energy in appropriate wavelengths falling on their chloroplasts. For a particular leaf this is a function of the distance from the source, the percentage of generated light actually making it into the tank, and the amount that is absorbed by dirty tank lids, suspended solids in the water, algae covering the leaf, etc.

We use WPG because we have no better measure. There aren't many light intensity test kits on the market yet. You can get a submersible light meter, but they're a little pricey and a bit beyond most people's needs.

If you look at it, watts/square foot of tank size would be a better measure, since illumination of the tank's footprint is actually what we're after. The WPG measure tends to horribly underestimate the needs of very small tanks and overestimate the needs of large tanks. The old 3 wpg suggestion was probably most appropriate for tanks in the 40-75g range. Then again, as was stated earlier, watts aren't a measure of light at all. I'm sure that AH-supply's stuff is vastly superior to what was on the market when the 3 wpg thing was first suggested.

Bottom line - you need enough to meet the needs of the plants. In my tank I have 192 watts of spiral compact fluorescents in a DIY enclosure with no parabolic reflectors over a 46 gallon BF. This works out to about 4 wpg, but in reality probably compares with 1.5-2.0 wpg from an AH supply system. Spiral CFs have a ton of restrike and my non-existent reflector isn't helping any.

Even so, my HC is filling the foreground in nicely, P stellatus is growing well and is a nice magenta color, and blyxa is growing like crazy. Could I use more? The didiplis is pink/red only at the tops when it gets close to the lights and my Ludwigia arcuata, R rotundifolia, and L repens only have great coloration within a few inches of the tank's surface. I'd say a little more would help.

The biggest reason that I'd like to upgrade to AH Supply quality is to cut down on my wasteful power consumption. 100 watts x 11 hrs /day x 5 years = lots of pizza money.


----------



## random_alias (Nov 7, 2005)

Yes. Luckily there have been some changes to the WPG Rule. More and more, people have become aware that it is in fact _not_ a rule.


----------



## hoppycalif (Apr 7, 2005)

It is not a rule, but we all need a guide when we set up an aquarium as to how much light to provide. That is all the watts per gallon "rule" ever was. Without it people were assuming that the light that came with their tank was good to grow plants with. And, in order to tell them it isn't, we have to be able to provide some guidance as to what would be good to grow plants with. In addition, when we are trying to decide among various lighting options, we need something to use to evaluate the options. So, I don't think we should dismiss the watts per gallon "rule", just explain it better.


----------



## BryceM (Nov 6, 2005)

I agree with you Hoppy, but people really do need to educate themselves a little about the subject if they want to spend their $$ wisely. People who are new to the hobby tend to see things in black and white. They latch on to the concept of 3 wpg and won't let it go, not understanding the variables that come into play.

I'd be willing to go out on a limb and say that most people would be happier, on average, if they stuck with moderate lighting. 3 wpg of older equipment probably meets this perfectly. You can grow just about whatever you'd like with this kind of light. The colors might not be as intense and things might grow a little more slowly, but there aren't many plants out there that would fail with this kind of light, provided you were meeting their other needs. 4 wpg of AH-supply stuff is probably overkill for anything bigger than 20 gallons. Lots of people do it with great results, but it's probably not the best way to start out. People just need to understand that (like everything else) they're often comparing apples & oranges when looking at 2 lighting products. Just because it says 55 watts on the box doesn't mean it puts out anything that resembles the light from a different setup that also happens to use 55 watts.

Lighting tends to be one of, if not the most, expensive piece of equipment in a typical setup. Getting something that you'll be happy and succesful with is worth doing a little research.


----------



## Raul-7 (Feb 4, 2004)

What's surprising is how regular T5's are more "effective" than HO T5's and MH? Based on the chart.


----------



## czado (May 26, 2005)

Raul, the difference in efficiency is offset by wattage for a given bulb length. For example, at 48" T5 is 24w and T5HO is 54w.


----------

