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 jakinthebox 05-02-2013 06:10 AM

WPG calculation & low, medium & high light?

Hi, I'm trying to get new lighting and pick plants for my tank and I need a couple of things clarified. Firstly how many watts per gallon is low, medium and high light? Is 2 wpg low or medium light? Secondly do I choose my lighting on the maximum capacity of my tank or by the actual amount of water in there. For example my tank is an 84 gallon tank but taking into consideration substrate, rocks, wood etc I estimate the actual volume of water would be more like 65 g which do I use for wpg ratio?
Thanks!

 Quantum 05-02-2013 08:14 AM

your questions illustrate why this method of determining lighting requirements is inexact at best and almost completely useless at worst, and this is without even getting into the different types of lighting - some produce more light per watt than others

it might be easier just to list the tank dimensions and intended plants and let others comment on their experience with various lighting options

 JDM 05-02-2013 09:28 AM

Yah. Distance to the bottom is more of a factor than water volume. A tall tank will need more watts for substrate plants to receive adequate light. Then there are tubes, CFLs, LEDs which cannot be readily compared based on wattage anyway.

If you have fixtures that give a lux measure (some do and for one or two different depths) then 1,500 to 2,000 will be a good low through medium light plants (I have about 1,700 is what I have, 8 Watt LED array, and it works for almost everything that I have tried so far, 3 failures out of about 30). Surface plants will impact this as well. I am finding that I need more light because of this so in hindsight I would consider going higher than needed and adding more surface coverage to compensate, plants, physical shading etc.

Some are using the PAR measure now which makes more sense but I don't know if the fixtures will be rated with this as often in order to compare.

Jeff.

 jakinthebox 05-02-2013 11:45 AM

Good point, tank size is 60 x 18 x 18in I don't want to go too high tech and freak the fish out with too much light but still want to grow plants with 'low to moderate' lighting requirements. Was thinking of a combination of daylight 65000k and something with a blue/red spectrum? I have not seen a lux measure on any of the lights/bulbs I've looked at (or listings I've seen). At risk of sounding like a fool here :oops: but what is lux anyway? Any help would be appreciated as the whole lighting issue has me a bit :shock:

 JDM 05-02-2013 12:22 PM

Quote:
 Originally Posted by jakinthebox (Post 1943850) Good point, tank size is 60 x 18 x 18in I don't want to go too high tech and freak the fish out with too much light but still want to grow plants with 'low to moderate' lighting requirements. Was thinking of a combination of daylight 65000k and something with a blue/red spectrum? I have not seen a lux measure on any of the lights/bulbs I've looked at (or listings I've seen). At risk of sounding like a fool here :oops: but what is lux anyway? Any help would be appreciated as the whole lighting issue has me a bit :shock:
The lumen is the measure of the total light energy output of a bulb.

The lux is the measure of how much of that light energy arrives over a given surface area, this is the intensity... 1 lux = 1 lumen/meter squared.

For example, a light with an overall output of 1,000 lumens that is focused on an area 1 meter by 1 meter results in 1,000 lumens per square meter or 1,000 lux. Raise the fixture and the lux drops as the focus of the light covers a larger area.

This avoids the whole watt comparison. I think the downside is that this has more to do with the light as seen by human eyes and it falls short unless tied in with the light spectrum components, which is where the 6,000k comes in. Using the lux and the spectrum get us in the ballpark for plant light needs.

Jeff.

 Byron 05-02-2013 12:31 PM

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I can certainly help with T8 lighting for the tank you mention, but bear in mind there is also LED and this I have not tried. LED is making great strides these days, it is still a very new concept, and if one knows what they are getting, it can provide good light. But it can also be a failure...and it is very expensive compared to T8.

I use T8 over my tanks that have fluorescent tubes. The "T" refers to the diameter of the tube in 8ths of an inch, so a T8 is 8/8 or 1 inch diameter; a T5 would be 5/8, etc. But these are not interchangeable, so the fixture has to be made for T8 or T5. The older T12, which was the original fluorescent tube, is being phased out as the T8 and T5 are more energy efficient, less damaging to the environment, etc.

I have a 5-foot 115g tank which is close to yours, only 6 inches deeper. I use two T8 tubes and you can see the plant growth in the attached photo. This is what I would go with, two 48-inch T8 tubes. There are several manufacturers of these, check fish stores or online suppliers (probably will be less expensive online). If you're gifted carpentry-wise, you can make a hood with a "shop tube" fixture.

As for the tubes themselves, you want at least one to be from 6000K to 7000K. "K" refers to Kelvin, the colour temperature of light. Scientific studies have shown that aquarium plants respond best to this light. The second tube can be the same, or it can be warmer or cooler. These terms refer to the white tone, warmer having more red and cooler having more blue. I won't comment further on this now, but we can pursue it later. I use tubes with a 6500K or 6700K rating, these are shown in the photo. In your case, for low and moderate light plants (which is what you see in the photo), you can use the less expensive tubes made by GE, Sylvania or Phillips; all three make a "Daylight" with 6500K, and I use them.

Byron.

 JDM 05-02-2013 12:39 PM

I don't know about florescents so I like reading these posts. I use LED but the lux allows to compare any bulb with another.

Jeff.

 Byron 05-02-2013 01:18 PM

Quote:
 Originally Posted by JDM (Post 1944234) I don't know about florescents so I like reading these posts. I use LED but the lux allows to compare any bulb with another. Jeff.
Following Karen Randall's advice (she is a long-standing member of the Aquatic Gardners Association) I also use Lumens or Lux as a guide, as one or both of these is sometimes given for fluorescent tubes. I appreciate that others think this is a false measurement, but it works for her and has for me in the experiments I did on my 29g.

 JDM 05-02-2013 02:48 PM

Quote:
 Originally Posted by Byron (Post 1944474) Following Karen Randall's advice (she is a long-standing member of the Aquatic Gardners Association) I also use Lumens or Lux as a guide, as one or both of these is sometimes given for fluorescent tubes. I appreciate that others think this is a false measurement, but it works for her and has for me in the experiments I did on my 29g.
I didn't really mention lumens as that is the total output of the bulb. The issue with that is the reflector or lens will affect this. A straight fluorescent bulb might put out 3,000 lumens but with no reflector you might get 300 lux at 20", a good reflector might bring that up to 2,000 lux (example only). The reflector can make or break the light level... which is one of the reasons I like LEDs, they are not so much reflected as they are focused... which is part of their efficiency as well as less heat... more of the light produced goes where you want it so you don't have to put out so many lumens to get equivalent lux.

Jeff.

 Geomancer 05-03-2013 09:33 AM

The LEDs I used in my custom fixture produce about 685 lumens each. That's close to a typical 18" T8 flourescent that does 750 lumens.

However, like mentioned, an LED has all that energy focused (in my case, a 120 degree cone) while a flourescent is omni-directional.

Those suckers are so bright they literally blind if you look right at them. I probably should've gone for lower power, and more numerous than just two individual high power LEDs ;) They work though.

The only commercial LED fixtures I've seen that people have had success with and you can easily find in stores is the Marineland Double Bright.

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