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WPG rule= Bull

4K views 30 replies 18 participants last post by  plantbrain 
#1 ·
I'm wondering why everyone still uses watts per gallon. Reef keepers have proven it to mean nothing. Shouldn't we use PAR readings instead.
 
#2 ·
If you read around, most folks here don't use the wpg rule anymore, much like reefers.

As for PAR measurements though, I've yet to see another member aside from Tom Barr that measure PAR readings. I guess it's not that critical as plants can deal with low and high PAR readings, much unlike corals.
 
#5 ·
I use and setup my tank using PAR readings (photosynthetically active radiation; the wavelengths of light used by plants and phytoplankton in photosynthesis) , I'm also a reefkeeper.
I haven't read anything in a long time using WPG, some people talk about lumens but I believer PAR is the most important measurement for any photosynthetic organism.
 
#7 ·
I'd agree in most cases, but this is the first I'm actually hearing about PAR. Did a little research on wiki and other searches, but couldn't find much useful for keeping plants. Is this the difference in light emitted from the bulbs for different types of tanks (fresh vs. salt)?

what's the complicated math and science? i'll take a stab at it if someone has more info.
 
#8 ·
It's really only complicated as far as you need a meter to make the PAR readings and they are not cheap or easy to come by.

If you frequent the reef forums you may be able to piece together various PAR readings for various bulbs in various fixtures at various distances.

Fact is, the info is more useful when setting up a tank. Once you have your fixture you might be able to adjust the plant choice, but you can not do a whole lot to greatly increase PAR output other than buy a new fixture.
 
#9 ·
PAR are the wavelengths of light that can be absorbed by chlorophyll. You can actually adjust PAR by moving your lights up and down, also by having the right combination of bulb/ballast. The only issue for me so far is that finding information of PAR needs for specific plants is hard, on the other hand there is a lot of info for corals so its easier to place them in the aquarium. For plants you only find info like light requirements: high, medium, low but they don't tell you what is high light, medium light, etc.
Lux and lumens are a measurement of light for the human vision and not the way plants see light, that's why I believe its wrong to base you light selection on lumens or lux. There are some types of light out there that have a high rating on lumens but the PAR is lower that other types.
 
#16 ·
Hummm...someone that uses PAR?

Well, what are the ranges for say HC?
Hydrilla?
Other common weeds?

From LCP to the maximum usage?
LCP= where Photosynthesis = respiration and maintenance
Max uyse: where adding more light does not increase growth rates under non limiting CO2, O2, nutrients etc.

For HC is about 25 for LCP to about 600 Max.
That ain't much and considering everyone carrying on about how HC is a high light plant, seems a bit fishy to suggest that it is.

So there is one example I bothered to test, there's a lot of data out there for about 30-50 plants. But few aquarist bother to keep.

I use WPG in general.
I've yet to see it fail on tanks from 10 gal to 1600 gallon.
You can extend the range from 2-4 to 1.5 - 6 if you wish, but you can grow most plants at 1.5 w/gal.
But 2 W/gal is a pretty good target for most folks' goals.
If you like to garden, consider higher wattages, if you are lazier, do not even think about it. If you are smart and have some dough, try using low light(T5's or PC's) + HQI for the option to use either or both to control, rates of growth(say when your folks come to town and you know you are not going to keep up on the tank). Or run it faster with more HQI's and garden more and trim more to get ready for a pic or a show or an open house etc.
There are options and trade offs with each amount and set up.
I'm into the hobby, so I like option 3.
You might not be, so lower light might be best for most new folks.


Regards,
Tom Barr
 
#10 ·
Its just an old thumb rule more or less, its not that big a deal these days. Knowing what fixture you're getting shows what you can grow IMO not WPG since lights keep getting more efficient. I think if par meters where more common you would hear more talk about it over here.

Plants are easy to grow on the majority though, so besides those select few its not really necessary for most of us. (Especially me with moss:icon_roll )

So yup you're right:thumbsup:
-Andrew
 
#12 ·
i recall seeing talk about using a lux meter combined with filter film to cut out almost all the green, makes it a lot cheaper, the problem though is there are no set values to compare the results with.
 
#13 ·
Problem is most people don't own tools for measuring PAR, lumens, etc. They are expensive and not commonly used unless you are more serious/technical about plants.

Sometimes local fish clubs pool together money to buy one of these readers to share.

On the other hand, plants are very adaptable in large and thus can adjust to less than ideal lighting.

So wpg is just a rough measure that happens to work most of the time.
 
#27 ·
Problem is most people don't own tools for measuring PAR, lumens, etc. They are expensive and not commonly used unless you are more serious/technical about plants.

Sometimes local fish clubs pool together money to buy one of these readers to share.

On the other hand, plants are very adaptable in large and thus can adjust to less than ideal lighting.

So wpg is just a rough measure that happens to work most of the time.
This is exactly what I was going to say, perfectly put destr! :thumbsup:
 
#23 ·
No, you folks need to measure in the planted tanks and measure the specific plant species.

We can use data from research and from nature as well to some degree.
Van et al, 1976 did some work, a lot of this type of work is no longer done it seems.

some from Barko:

http://www.jstor.org/view/00129615/di960461/96p00385/0

Bowes:

http://www.sciencedirect.com/scienc...rid=4421&md5=82a3bed9bf208e2554b63494e47f5810

Some of them you cannot not access through the web.
Sorry, old school research background look ups:hihi:
You folks have it easy these days.

But if you do not know what to look for and how to apply it, it's of no use to you.:icon_idea

Regards,
Tom Barr
 
#29 ·
Well PAR isn't the end-all either. Unless I am mistaken, it is unweighted energy between 400-700nm... this doesn't take into consideration the plants sensitivity to specific wavelengths... isn't that called PUR (photosynthetic useful radiation)...

WPG is just a rule of thumb, not law, and assuming your talking about bulbs with similar spectra in the normal ranges, a rough correlation with PAR/PUR can be assumed. So, lights very in there efficiency, like T5 blowing away CF which blows away T12... that has also been accounted for. Folks have even made charts with effeciency factors for T12 vs T8 vs CF, etc, etc. Most factor in size of tank also, knowing it takes more for little tanks and less for big tanks. No its not an exact science, and as soon as better data is available from manufacturers, or cheaper light meters, or more info on the net, I am sure folks would be using it.
 
#31 ·
I do not think you will ever get that exact with light and CO2 and nutrients.
So a rough gauge works, plants have variation, so do all biological systems, they can adapt to a give range of conditions.

You can test light with PAR meters, which is what most researchers do.
Even there, there's debate about it.

But that's the best we can really do.
You can measure the plants also, their output of O2 relative to a light source or intensity. Now you have a biological measurement for light.

Making a light curve for photosynthesis of a species is a good study.
So I vs O2.
You get a nice curve that levels off.

Most aquatic plants that have had light curves done, leveled off at 600 micromol. Minimum ranges are about 12-40 micromol.

So even if you had a PUR meter, you'd still need to see that for every plant species, that "PUR" would also be different. Rarely are the exactly the same, which is why PAR is accepted, it's fairly even.

Then there's our own weird color perception and desires with light.

Regards,
Tom Barr
 
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