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Discussion Starter · #1 ·
I'm setting up a new 58-gallon planted tank. I have a good deal of experience with planted tanks but I need some current lighting expertise. The tank is 36-inches long and 24-inches deep and I'm not sure that power compacts, which I've always, used is really good enough. Would it be for a tank that deep for a variety of plants including some higher-lighting plants? If it is, how many 96-watt bulbs over it? If not, what is a good alternative. Thanks
 

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I dont think that depth would be a problem, check out this company Compact Fluorescent Lighting Kits

Good price and the reflectors will get the light down where you are worried about it getting. I would go with 2 96 watts over your tank. Go to the site and click on the 96 watt kit. If you arent handy with DIY stuff dont worry they make it very simple to setup the lights and you can even buy and enclouser through them
 

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Discussion Starter · #4 ·
I have a 75-gallon planted tank now with over 5-watts per gallon and I never really got good growth in the lower part of the tank out of the power compacts that are on there, and that has the same depth as the 58-gallon that I'm setting up. That's why I'm wary of going with the PCs again. I see that the t5's are getting more popular all the time for reefs so I'll look into that. The two free 6,500K bulbs make that unit at ReefGeek attractive.
 

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I also have a 90 gallon that is 24" deep. I had a bunch of pc's over it and had similar issues with the lower parts being leggy. I switched to a T-5 HO Tek fixture and it helped a bunch. They seem to penetrate much better. I think maybe a metal Halide may be better but the T-5 HO is a good cheaper alternative. Runs alot cooler too. I also have some friends that use the 96w PC over there 24" and deeper tanks with good success. Maybe they penetrate better than the 65w ones. I dont know. I also have heard that the AH supply kits work better too because the reflectors are better.
 

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Metal Halide baby! It's expensive and hot, but you get a great source of light. I have a new setup with 150W HQI's and T-5's over a 24" deep tank. The MH's really penetrate to the bottom nicely.
 

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guaiac_boy said:
Metal Halide baby! It's expensive and hot, but you get a great source of light. I have a new setup with 150W HQI's and T-5's over a 24" deep tank. The MH's really penetrate to the bottom nicely.
I have two (and sometimes three) AHSupply 96W PC lamp/reflectors over my 90 gallon and it just doesn't quite do it. I'm considering adding these:

Catalina Aquarium



So the 150W HQI have some 'punch'?
 

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MH are amazing, but they are not a super solution for your tank. You can certainly put two over it (one will not be enough light spread), but that is a lot of light to manage....and expensive. I would go with the t5 solution. If you are that worried about penitration, get the 6 bulb version and stagger the lighting.

jB
 

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Jason has a good point. I think MH's are fabulous, but they are probably best used for only a few hours a day (4-6 hrs). This means you need an additional light source if you like to actually see the inside of your aquarium.

When it's all said and done, light is light. There isn't anything magical about the light coming off of MH's that makes it penetrate deeper into the water. Wavelenghts are slightly different from bulb to bulb, but this is also true with fluorescents.

Just for the record, CF's are nothing more than T-5s that have been bent in half. There really isn't much difference, except that T-5's are probably a little more efficient with good quality reflectors since there is less re-strike.

If you do decide to go with MH's alone, I'd reccomend using hanging pendants so that you can get them up off of the water a little.
 

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guaiac_boy said:
Jason has a good point. I think MH's are fabulous, but they are probably best used for only a few hours a day (4-6 hrs). This means you need an additional light source if you like to actually see the inside of your aquarium.

When it's all said and done, light is light. There isn't anything magical about the light coming off of MH's that makes it penetrate deeper into the water. Wavelenghts are slightly different from bulb to bulb, but this is also true with fluorescents.

Just for the record, CF's are nothing more than T-5s that have been bent in half. There really isn't much difference, except that T-5's are probably a little more efficient with good quality reflectors since there is less re-strike.

If you do decide to go with MH's alone, I'd reccomend using hanging pendants so that you can get them up off of the water a little.
i have used nothing but halides for my reefs and, most recently, my fw planted tanks.

metal halide does a better job at depth penetration due to its unique method of illumination via a point source of light rather than the emmission of light throughout an entire length of flourescent tubing. the point source allows deeper penetration of light to the deeper parts of the aquarium.

par of metal halide is also higher than flourescents with cri very close to that of natural sunlight (though a lot of cf and t5's have great cri nowadays also).

metal halide is a little different to use that flourescents. i absolutely agree that the best method for ANY metal halide use in an aquarium situation is via pendants. the amount of heat they generate is much more easily dispersed into the surrounding air than having them enclosed in a hood (even with fans blowing in to circulate the air).

finding the right bulb for fw plants is also tricky esp for double ended bulbs (de and some refer them to them as hqi).

here is the de bulb that i use. it took a while to locate but does as absolutely phenom job at plant growth.

customaquatic.com

LT-US150-52
Price $49.99
Ushio 150 watt 5,200K metal halide lamp with double ended HQI type RX7 base...

i use it in a hamilton reefstar reflector pendant with an electronic ballast (very quiet) with low heat emmission.

hth's a little! :)
 

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In my opinion the loss of light due to water depth is a highly overrated "problem". You just can't lose much light going through only 24 inches, no matter what the type of light. One possible problem you can have is to have a spectrum that is too loaded with wave lengths that water absorbs more strongly - meaning red light. But, for the 5500 to 10,000K lights we use, that shouldn't be a problem. Once the light strikes the water surface at a steep enough angle not to be mostly reflected, all of it will reach the bottom of the tank with only 20-30% loss at the worst. And, that just means using a good reflector for whatever light you use. White paint doesn't work that well, because it diffuses the light, making it hit the water at all angles, including angels too shallow for much light to cross the water/air boundary. So, a polished aluminum reflector, that lets you see a good reflection of all surfaces of the bulb when you look up into it is the ideal.

The above, as I said, is my opinion, but it is based on considerable knowledge.
 

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A bigger problem than the ability of light to "penetrate" through a given distance of water is the natural reduction in intensity as the distance from the light source increases.

Physics tells us that if you double the distance from a point source of light the intensity will fall by 4 times.

The intensity of light 6 inches from the source will be sixteen times greater than at 24 inches. Ever wonder why your stem plants color up nicely near the surface? Poor little HC has to live on whatever it gets.

The intensity of light at 18 inches is 1.8 times greater than at 24 inches.

As always, simple math & physics principles come into play. The problem isn't due to some mysterious property of light and water.
 

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guaiac_boy said:
A bigger problem than the ability of light to "penetrate" through a given distance of water is the natural reduction in intensity as the distance from the light source increases.

Physics tells us that if you double the distance from a point source of light the intensity will fall by 4 times.

The intensity of light 6 inches from the source will be sixteen times greater than at 24 inches. Ever wonder why your stem plants color up nicely near the surface? Poor little HC has to live on whatever it gets.

The intensity of light at 18 inches is 1.8 times greater than at 24 inches.

As always, simple math & physics principles come into play. The problem isn't due to some mysterious property of light and water.
Hey! I love a good physic argument!!
If you have a point source of light the intensity does drop by the square of the distance from it, because the surface of a sphere is proportional to the square of the radius, but if you use a reflector to direct all of the light into a perfect parallel beam, there is no drop off with distance unless the light is absorbed or reflected in some way. Of course there are no perfect reflectors and no parallel beams, but a good polished aluminum reflector comes close enough for a 24 inch distance. Ding! End of round one!
 

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round 2....

I agree that a good reflector helps. I disagree that it results in anything close to a parallel beam of light. What it is supposed to do is make use of the light emitted upward and to the sides, redirecting it in the general direction of the aquarium.

In my current setup, my MH fixtures measure about 10" x 5" and they sit about 8" above the water of my 24" deep tank. If they did, in fact, produce a nice, tight, parallel beam of light then there would be a bright spot on the substrate exactly 10" x 5" in size. The remainder of the substrate would be unlit. In actuality the light spreads out VERY quickly - so quickly that the entire surface of the tank is brightly lit. In only 8" the light has spread out to cover an area 24"x24".

Think of a high-quality flashlight. You get a reasonably tight beam of light. Still, it spreads out with distance. The average aquarium reflector, even the "good" ones, don't come close to this level of precision, nor would we want them to.

The truth is that nothing in the hobby that we use (except maybe LED's) acts like a point source. MH's are close. Fluorescents are definately NOT point sources. Reflectors do help, but I think a light meter would easily show that intensity drops off quickly with distance. Anyone have a meter that could check this out for us?
 

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Yes, in air, the intensity drops offf fairly rapidly with distance, but not as the square of the distance. But, once the light enters the water, the water, with glass walls, acts as a light pipe, and the drop off isn't nearly as much. So, if the light sits right on the water (impossible, of course) there isn't much drop off at all - sitting on the top of the tank isn't quite that good, but still good. One way to do a crude test is to check how much light is "spilling" out through the glass walls, by looking at the light on the floor, the stand edges, etc. to see how big the light "footprint" is. Again, if the light sits on the tank, that footprint will be not much bigger than the tank. Ding! End of round two.
 

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Discussion Starter · #16 ·
This has been great information. I know something about MHs as I have them over my reef. There's no question about their ability to penetrate deeper than PCs (at least, a lot of 65-watters) which is what I had used before I got the MHs. But they do generate a lot of heat. And this room, with all of the tanks that I have, get's really warm and I resorted to a hefty chiller for my reef. That's not an option for the new planted tank so there'd be a whole lot more heat in the room than there already even is with two MHs which is what I'd need for this tank, so I'm now teetering between the 96-watt PCs and the t5's. Seems to me that the t5's generate less heat though, wouldn't they?
 

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The T-5's will run cooler than the metal Halide.


Ok I have one issue here, your trying to tell me than the lighting wont drop off as much as in the air? WHAT? are you joking? So the lighting goes through water easier than the air? I think not. Maybe a better description of your meaning will help me understand better.
 

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chiahead said:
The T-5's will run cooler than the metal Halide.

Ok I have one issue here, your trying to tell me than the lighting wont drop off as much as in the air? WHAT? are you joking? So the lighting goes through water easier than the air? I think not. Maybe a better description of your meaning will help me understand better.
The reflectors we use are far from optically perfect, especially with light sources that are far from point or line sources. So, there is a dispersion of the light when it leaves the reflector, that reduces the intensity of the light as a function of the distance it travels from the reflector. That reduction is not proportional to the square of the distance, but it is a reduction.

Once the light enters the light pipe (think fiber optics), which a rectangular tank filled with water is, it has a different way of losing intensity. Virtually all of the entering light will be at angles that are very highly reflected back into the water by the glass-water interface. So, no more loss just due to dispersion. Instead, the water absorbs light at some wave lengths - at all wave lengths, but over a two foot length only the red end wave lengths get absorbed significantly. And, the lights we use typically are 5500 - 10,000K lights, without a lot of red wave length energy, so without a lot of absorption by the water.

That's how I see it, and that's what I meant. Incidentally, an aquarium is far from a perfect light pipe, just as our reflectors are far from perfect. So, this is not meant to say that no light reflects out of the tank, only that it is a small amount. So, I think my position that up to a two foot depth, all lights we might use are equally able to penetrate to the bottom, is correct.

MH lights are typically high wattage lights, compared to T5 or PC, so that fact alone says they get more light to the bottom of the tank, just as higher wattage PC or T5 lights would.
 

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well I dont know about the science or mathamatical end of this subject. I only have my personal experiences. When dealing with my 90 gallon, I originally had a 4x65w PC fixture over it. I had serious issues growing any low foreground plant that was considered med to high light. Stem plants were also very leggy at the bottom. I then added another 2x65w PC fixture for a total of 6x65w of PC's. Results were a bit better but not very much. I grew tired of trying different stem plants that wouldnt get as leggy as others and with the lack of foreground choices. I then moved to a 8x54w T-5 HO Tek setup. What an extreme difference that made. I could finally get some better choices in there and the foreground stayed low and actually lived. Now with some math.

6x65w=390w of PC

8x54w=432w of T-5 HO

not a huge difference in total wattage. I know the reflectors on the Tek light are much more efficient than the PC setup, so maybe that was the huge difference. Either way with the differences in the growth is more than enough evidence for me that all lighting penetrates the water about the same.
 

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Hoppy, one thing to factor into the "light-pipe" idea is that the sides of the aquarium don't make very good reflectors. Some light passes through to the room and is "lost" (actually if it wasn't, we couldn't see the stuff inside ;)), some light is reflected back into the tank, and a lot of it is absorbed instead of reflected.

I still think it would be easy enough for someone to get a waterproof light meter that could demonstrate the effects of light intensity in air vs in water at various distances from the source. That would answer the question pretty easily IMO.
 
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