Wpg

[codeajohnson]

Hello Everyone,

This is a pretty simple question, but I wanted to make sure I was doing this right. To figure watts per gallon, I just divide my total wattage by my total volume? So I have two 15 watt lights that came with my tank. So I would divide 30 by 55, which is about .54 wpg? Is that correct? Thanks for any help.

 

[Ian H]

if you have 30 watts of light in a 55gal tank you have 1.8wpg

to work it out you just divide the gallons by the watts, so 55/30. Hope that helps

 

[Fishlove]

Yeah, you got your calculation the wrong way round; it's volume / watts. So yeah, 1.8.

 

[Dave Spencer]

You have 0.54WPG, which isn`t a lot of light. Not that the WPG rule is particularly accurate.

Dave.

 

[Ian H]

god! of course its .54 not 1.8!!!

seeing as 30 is almsot half of 55!!

Can't believe i got that wrong! ha ha I used to go by the wpg rule (although looks like i was doing it wrong any way ) but soon learnt it doesnt mean a great deal, same as with the inch of fish per gallon.

What size tank you got? im assuming your worried about plant growth and thats why your asking?

 

[iankent]

to work it out you just divide the gallons by the watts, so 55/30. Hope that helps

dividing gallons by watts would be gpw not wpg surely - I'd think it's 0.54 too!

e.g. mpg = miles per gallon, e.g. 350 miles / 13 gallons = 26.92mpg

 

[Fishlove]

Well. I was complete absolutely stupidly wrong MY bad!

 

[Ian H]

to work it out you just divide the gallons by the watts, so 55/30. Hope that helps

dividing gallons by watts would be gpw not wpg surely - I'd think it's 0.54 too!

e.g. mpg = miles per gallon, e.g. 350 miles / 13 gallons = 26.92mpg

Yeah, no idea why i was thinking like that! i blame grolsh

To the OP .54 wpg is rather rubbish (just over half a watt per gallon) but that doesnt mean you can't grow plants!!

Java fern will hapily grow in that kind of light so will java moss, fairly slowly but better than plastic plants! Theres quite a few low light plants, your best bet would to have a look/ask in the planted forum. Plus you could always get reflectors to add that little bit more light into the tank

 

[orange shark]

what lighting are you reccomended to have?

 

[OldMan47]

That depends a lot on what plants you have orange. For very low light plants like java moss which will almost grow in the dark, you are fine. For typical low light or even medium light plants you will want about 1 1/2 to 2 wpg. Although the wpg rule "doesn't work" it is actually a very good measure for a 55 gallong tank. I think whoever invented it must have been using a 55 as a reference.

 

[iankent]

how does energy saving lighting impact on wpg? for example, if your using a 20W energy saver thats equivalent to 100W, in a 10G tank is that 2wpg or 10wpg?

 

[pastabake]

Are you sure that you have a 55 gallon tank and not a 55 litre? Because the 15w tubes are normally ~2ft which unless you have a deep cube shaped tank they wouldn't even begin to cover a 55g tank.

The WPG is in my opinion pretty worthless anyway ... but as it goes it works only when comparing like for like ...

Treat it with caution because it is based on assumptions -

1.) That fluorescents give out a constant lumen per wattage ... obviously while this might have been partially true back in the days of T8's. Today with the choice of HO & VHO tubes, T5's, etc., it isn't. (not even mentioning metal halides)

2.) A standard tank depth, because for every ft the amount of light halves ... i.e. 15W on a 1ft tank is going to be twice as good as 15W on a 2ft deep tank.

3.) That your tubes give adequate coverage. i.e. a single high power tube at the back of your tank may provide high lighting directly under it but towards the front of the tank it wont .... obviously this becomes more important once you have plants because shading will play an increasingly important role in limiting light penetration.

and that isn't even considering the spectrum of the bulb and its true PAR rating ...

 

[codeajohnson]

Thanks for the help everyone. Yes, I am using a 55 gallon tank. It came with two 15 watt tubes, that are about 2 feet long. They are end to end, making up close to the 48 inches in length. I am planning on trying to put riccia in my tank, as well as some swords. I was wondering if I should up grade to more wattage? I would be willing to put money into the tank if I have a better chance of growing plants. I also have 2 nutrafin CO2 kits ordered as well. Thanks for any advice!

 

[Ace Of Spades]

Thanks for the help everyone. Yes, I am using a 55 gallon tank. It came with two 15 watt tubes, that are about 2 feet long. They are end to end, making up close to the 48 inches in length. I am planning on trying to put riccia in my tank, as well as some swords. I was wondering if I should up grade to more wattage? I would be willing to put money into the tank if I have a better chance of growing plants. I also have 2 nutrafin CO2 kits ordered as well. Thanks for any advice!

Id alteast try and get 2WPG if you can, as that is a nice starting point IMO. And I think Riccia needs higher light which is pointed out [topic="101806"]HERE[/topic].

Many Thanks
Ace Of Spades

 

[OldMan47]

To answer iankent's question, the wpg numbers that are used relate to only normal output fluorescent lights. The so called energy savers are fluorescents that are being compared to the very inefficient incandescents. The 13W that is called a 60W equivalent counts as 13 watts, not 60. As pastabake said, other types of lights can produce the same light with less power or can be overdriven to produce more light from the same bulb. The WPG "rule" only applies to normal output T-8 or T-12 bulbs. The real comparison needs to be made based on light output that is falling on the tank. That means it is affected by reflectors as much as by HO, ODNO or other configurations. Furthermore, the light ratings in terms of light (lux)relate to light as it appears to a person so the spectrum at the top stops at violet, even if the lamp has a lot of UV, and stops at the bottom at red, even if the lamp has a lot of infrared. The lux rating ignores the added light that a plant might use but people don't. When you look at some of the lamps specifically designed for plants, many of them seem rather dim and pinkish in color for the amount of power they consume but what you can't see (because you are a people) is what the plant is using to grow.
Back to basics, watts mean almost nothing unless they are considered in context. In context they can be related to the amount of light output and thus the light available to a plant.