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Lighting Science of Aquatic Lighting - Aquarium lighting is essential for healthy aquatic plants. Discuss proper aquatic lighting for your plants and fish here.

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Old 10-16-2007, 02:03 PM   #21 (permalink)
 
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Default Re: Proper Wattage for Aquariums

mine 50L (55x30x30cm),2x40w, and 2x15w..... total 110w.
plants doing well with ferts and perssurised co2.
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Old 10-17-2007, 02:46 AM   #22 (permalink)
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Default Re: Proper Wattage for Aquariums

lol mine is the 20gal.long and i have 102w over it lol!
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Old 10-24-2007, 08:21 AM   #23 (permalink)
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Default Re: Proper Wattage for Aquariums

I have a standard 125 Gallon tank, and 220 watts is not enough to get glosso to stay down. I currently have power compacts. My CO2 is good enough, just lacking on the lighting. The glosso does product the bubbles, but it is not staying down.
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Old 03-06-2008, 01:29 PM   #24 (permalink)
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Default Re: Proper Wattage for Aquariums

While acknowledging the fact that lumens output varies with color temperature and spectrum of specific bulbs, etc., nevertheless, here are some rules of thumb for comparing light output. Because of the aforementioned caveats, they're rough, but that's usually expected of rules of thumb.

I based my comparisons on a survey (very non-scientific) of manufacturer's specifications for bulb output in lumens. I used the numbers for bulbs rated between 3000K and 4000K. That way I'm not comparing a bulb from one manufacturer at 3500K (high lumens) to a bulb from another manufacturer at 6500K (lower lumens). I used the nominal 4' length of bulbs for the fluorescent lights.

So what I found is that a T12 40 watt bulb is expected to output about 2900 -3200 lumens, or from 72 to 80 lumens per watt.

A T8 32 watt bulb is expected to output about 2900 lumens or about 90 lumens per watt.

A T5 (non HO) 28 watt bulb is expected to output 2700 - 2900 lumens or from 96 to 103 lumens per watt.

A T5 HO 54 watt bulb is expected to output 5000 lumens or about 92 lumens per watt.

Compact Fluorescents should be approximately comparable to T5 HO but a bit less efficient because they're the same technology but with some disadvantages.

Whether you actually get that many lumens, only a man with a light meter knows. But these should be useful numbers for comparison purposes. In other words, the numbers may not be right, but if they're wrong, with a little luck, they're all wrong in about the same way.

Similarly, these numbers will be too high for higher color temperatures which are further from the green/yellow light where lumens are measured, but presumably, a 6500K T5 bulb will be proportionately more efficient than a 6500K T12 bulb.

Additionally, the current crop of High Intensity LEDs put out about 80 lumens per 1.1 watt LED at .350A or about 72 lumens per watt. When run in high output mode at .7A they output 140 lumens at 2.38 watts or about 59 lumens per watt. LEDs are improving really fast right now, so these numbers may be out of date tomorrow, but remember, that you need to use LEDs for comparison which are actually shipping in usable/affordable quantity. Just because they can do something in the lab doesn't mean that you can put one over your aquarium.

For metal halide a 70 watt bulb produces about 6000 lumens initially falling to 4800 lumens fairly quickly. I'm not sure whether to use the initial or the mean, given the very short life of these bulbs, but it's between 70 and 85 lumens per watt. Maybe a lumen or two higher per watt for the higher wattage (150 - 300 watt) bulbs.

So in terms of energy efficiency, we have a rough rating of LEDs at the low end of the scale (surprise!) then T12 fluorescent and MH in about the same neighborhood, then T8 and T5 HO neck and neck, and finally T5 (non-HO) as the most efficient lighting. Notice that these numbers are close enough together and so approximate, that different fixture and bulb choices could cause the efficiencies to overlap. Again, this is a rule of thumb for comparison purposes.

HI LED: 59 - 72 L/W
T12: 72 - 80 L/W
MH: 70 - 85 L/W
T8: 90 L/W
T5 HO 92 L/W
T5: 96 - 103 L/W

But there are other ways to measure efficiency. We could measure areametric light efficiency. In other words, how much light intensity can we get in a unit area. Considering this parameter brings up several issues that should be at least mentioned, if not discussed.

First, the efficiency of the light's reflector has a substantial impact on how efficient your light really is. Fluorescent and MH lights emit in a tubular pattern and so need reflectors behind them to try to recover 50% or more of the light. LEDs may be more directional and therefore more efficient without a reflector. Also, the further from 90 degrees (perpendicular) the angle of incidence (angle between water surface and direction of travel of light) gets, the more light is reflected at the water's surface.

So for best light intensity, the ideal is a column of light striking the water surface perfectly perpendicular to the surface. For this comparison, we'll just assume that all the light is reaching the aquarium, or that the reflectors for each type of light are equally efficient. Keep in mind that this may do LED a disservice, because the light from LEDs is emitted pointed more or less towards the water and requires much less reflection to actually get there.

So assuming that a pair of T12s need a reflector 7.5" wide, a pair of T8s need a reflector 5" wide, a pair of T5s need a reflector 3" wide, a 70 watt MH needs a 6" X 8" reflector area and three HI LEDs occupy 1 square inch, we get the following:

T12: 16 - 18 L/in^2
T8: 24 L/in^2
T5: 37 - 40 L/in^2
T5HO: 69 L/in^2
MH: 100 - 125 L/in^2
HI LED .35A: 240 L/in^2
HI LED .7A: 420 L/in^2

Note that while it is theoretically possible to fit LEDs as densly as assumed above, there's a good chance that they would overheat that way. The commercial LED aquarium lights put them in at about 1/6 the density and use even less efficient LEDs (lower light output) to boot. So you could build an LED based aquarium light with the intensity listed above, but if you buy one, it's actual intensity will be close to a T5 HO or plain T5.

Also note that a square foot of LEDs at the density listed above would cost $2300 at today's prices, just for the LEDs. That's not even including the cost of current regulators and power supplies. LEDs last longer than fluorescents, but they don't last forever. They're expected to have lost a substantial fraction of their output at 50,000 hours.

In the aquarium hobby, we're usually limited more by how much area is over our tank, than by how much electricity we can deliver to it. So, if you could afford them, LEDs would be the best lighting choice for getting high intensity light in a small area. The next best choice (purely from a light intensity vs. area POV) is MH, and after that comes T5 HO.

The numbers above give a rough quantization of how the intensities compare.

Other factors we consider is the cost to buy the fixture and the cost of replacing light bulbs, but those types of numbers are readily available, so I won't bother with them here.

Those rough light output and light efficiency numbers above should help folks compare different lighting choices.

Specifically, when we discuss watts per gallon, it gives a little better basis for talking about watts per gallon of T12 vs. T5 vs. MH lighting.
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Old 03-06-2008, 11:32 PM   #25 (permalink)
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Default Re: Proper Wattage for Aquariums

Trag,

Great post. I'm curious about your LED info. I'd heard previously that their effeciency/watt was much, much better than the other light sources. Apparently you're saying that this might be possible someday, but that it is not true with currently available systems? There seems to be a discrepency between your info and what has been posted here previously.

Doing a little poking around on the web it seems that your info is fairly accurate. Hmmmm.

All of this still leaves us with a very limitted ability to recommend a certain "watt/gallon" ratio for a successful planted tank. Lumens aren't a great measure since they measure visible light, but not necessarily photosynthetically important wavelenghts. As far as a plant is concerned, what really matters is how much effective light energy a certain area of leaf is receiving at a given time.

Maybe watts per square foot (or per square meter) of tank footprint is a better measure.

Tank geometry and reflector design is enormously important too. Deep aquariums, elevated (pendant) lighting, and imprecise reflectors make a bad combination.

Last edited by BryceM; 03-06-2008 at 11:47 PM..
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Old 03-07-2008, 07:54 AM   #26 (permalink)
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Default Re: Proper Wattage for Aquariums

Quote:
Originally Posted by guaiac_boy View Post
Great post. I'm curious about your LED info. I'd heard previously that their effeciency/watt was much, much better than the other light sources. Apparently you're saying that this might be possible someday, but that it is not true with currently available systems? There seems to be a discrepency between your info and what has been posted here previously.

Doing a little poking around on the web it seems that your info is fairly accurate. Hmmmm.
I was surprised as well. A year or two ago I got enthusiastic about LED lighting, but being of an engineering mind, I started looking into what is actually available. When one goes to manufacturers such as Luxeon (Lumileds) and actually reads the specs on the datasheets for their high output LEDs, you find that they are not any more energy efficient than fluorescent lighting. The marketing claims about incredible efficiency, must be in comparison to old incandescents or something. However, as I mentioned in passing, LEDs may get a bump in actual energy efficiency because they are somewhat more directional in their light emission than fluorescent or MH. In other words, they may emit about the same light per unit energy, but more of that light may actually reach the target.

LEDs are also not a cool lighting source. They produce a lot of waste heat. An LED fixture with a high concentration of LEDs would need to have a metal back acting as a heat sink and some fans to provide active cooling.

Quote:
Originally Posted by guaiac_boy View Post
All of this still leaves us with a very limitted ability to recommend a certain "watt/gallon" ratio for a successful planted tank. Lumens aren't a great measure since they measure visible light, but not necessarily photosynthetically important wavelenghts. As far as a plant is concerned, what really matters is how much effective light energy a certain area of leaf is receiving at a given time.

Maybe watts per square foot (or per square meter) of tank footprint is a better measure.

Tank geometry and reflector design is enormously important too. Deep aquariums, elevated (pendant) lighting, and imprecise reflectors make a bad combination.
It is a complicated topic. However, I think that if we used the numbers I gave above as rough conversion factors we can sort of recommend lighting amounts in terms of lumens--only they aren't really lumens....

Sheesh, this is hard to explain, but not really that complicated. What we care about, I think, is light intensity. Each person lighting a tank may choose a different spectrum of lighting (different intensities at different frequencies) depending on what their needs are. So we're never going to be able to do a perfectly equivalent job of specifying light spectrum and intensity--at least not in any way that is useful to most folks.

But, we can get in the ball park by using the conversion factors in my previous post. According to those numbers, 1 watt of LED lighting is equal to from 6/7 to 1 watt of T12 lighting. 1 watt of MH lighting is about the same as 1 watt of T12 lighting. 1 watt of T8 lighting is about 9/8 - 9/7 of 1 watt of T12 lighting. 1 watt of T5 HO lighting is about the same as 1 watt of T8 lighting or, again, 9/8 - 9/7 of T12 lighting. And 1 watt of non-HO T5 lighting is about 4/3 of 1 watt of T12 lighting.

Once you know how many watts are needed from one type of light, you can convert it to a roughly equivalent amount of energy input (watts electricity) in another form of lighting using the numbers above. Of course, with the caveat that the spectrum needs to be similar for the results to be similar.

So, for example, if 100 watts of MH works well on a 30 gallon tank, then 100 watts of T12 lighting would probably work about as well, if you can fit it on the tank top. But 75 watts of T5 or about 80 - 85 watts of T5HO or T8 would probably do about the same job.

Or a very practicle example...

I have a 30 gallon long (36" X 12" X 16"H) with an old light I built 20 years ago. The light consists of two 30 watt T12 bulbs. How much more light would I get if I switched to a pair of T5 HO 39 watt light bulbs? Well I'd have 78 watts vs. 60 watts, which is 1.3 times the wattage. But, using the conversion factors above, 78 watts of T5 HO is about equivalent to 90 - 100 watts of T12 light.

So a switch from 60 watts of T12 to 78 watts of T5HO would be about like increasing the light by a factor of 1.5 - 1.66, not the 1.3 that the simple wattages imply.

Last edited by trag; 03-07-2008 at 08:25 AM..
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Old 03-07-2008, 09:53 AM   #27 (permalink)
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Default Re: Proper Wattage for Aquariums

My understanding is that white leds are not efficient at higher wattages and are better at lower ligh levels (this may only be due to not getting fluorescents to run really low wattage effieciently - the whole high voltage thing).
White leds operate by producing UV light and then it is flouresed into visible light (sound familar here). This is why LEDs tend to have a bluish hue to them.
The one advantage is the lifetime and ability to switch on-off alot. I don't know if the fluorescence would wear out on white leds.

The area where leds are efficient are colored such as red, and green. The reason being that normal bulbs create white (yellow) light and then are filtered to the desired color. Very inefficient. LEDs instead produce the color you want with no loss. Also again good at switching (long lasting), and the general lifetime. I.e. good for traffic lights.

I keep hearing about white led being more efficient in the technology publications and CNET etc, but no math. Those might be experimental or again low light level applications.

A church on the east coast (one during the American revolution with the lantern) is using white leds for highlighting the trim/ceiling. Again not too high of a light level, and better lifetime than other systems (hard to reach to change it).
http://www.cnn.com/2008/TECH/03/03/n....ap/index.html

For aquariums, I don't know what the spectrum would look like.
I know in the past before white led were avaliable people would combine red/blue/green/yellow etc to create a combined light that looks white. Again that would be for human eyes, wether the spectrum would be good for plants/fish etc would need further investigation.

Wikipedia quote "To produce a white SSL device, a blue LED was needed. In 1993, Shuji Nakamura of Nichia Corporation came up with a blue LED using gallium nitride (GaN). With this invention, it was now possible to create white light by combining the light of separate LEDs (red, green, and blue), or by placing a blue LED in a package with an internal light converting phosphor. With the phosphor type, some of the blue output becomes either yellow or red and green with the result that the LED light emission appears white to the human eye."
from the article http://en.wikipedia.org/wiki/LED_lamp

One led system is selling (expensive) and the idea is that one can have gradual light levels for the whole dawn, dusk, moonlight simulations.
Here's an example:
http://www.drsfostersmith.com/produc...=0033919000000
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Old 08-28-2008, 01:53 AM   #28 (permalink)
 
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Default Re: Proper Wattage for Aquariums

In the not-so-long time I've been keeping aquaria, I have determined a few things with relative certainty. Cheif among them: any rules tried to apply to stocking and lighting will fail miserably. An aquarium is part art, part science, and when you try to take the part of art's domain into science, you run into trouble. The "inch of fish per gallon of water" rule gets thrown around a lot at lower levels, but quite clearly doesn't work (foot long fish in a 20 gallon tank should then be quite roomy), and neither does wpg, or any derivative of it. It might take 50 metal halide watts to grow a carpet of Glosso in a 30 gallon tank, but you could probably do the same with about 20 VHO T-5 watts. A watt is nothing more than an amount of energy used and in no way relates to the amount of energy emitted as light (case in point, incandescent bulbs), and cannot be converted into any rule, just as the length of a fish cannot be plugged into some formula (within reason) to determine how much space it needs, as there will always be a number of other factors (activity, agression, pH, temperature, maintenance, filtration, swimming level, decor, social habits) that alter it. To say a plant needs x wpg fails to account for how much water the light has to penetrate and over what span, the emission of the light, reflectors, the whole fertilization scheme, and basic parameters. I could put as many watts of VHO T-5 light over my 55 gallon tank as I want, but if I have don't have the CO2 and fertilizers to keep up, all I'll grow is algae.
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Old 08-28-2008, 02:54 PM   #29 (permalink)
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Default Re: Proper Wattage for Aquariums

If I were just starting a planted aquarium I would have no idea how much light I needed. I would assume the light the tank manufacturer supplied with their tank would adequate, if barely so. But, beyond that I would be in the dark.

All that the watts per gallon "rule" is ever going to do is help people like me get somewhere in the right ball park for a good light intensity. Without that "rule" I would have to come to a forum like this, or, much worse, ask the LFS clerk what light or lights to buy. The answers I would get would range over a very broad spectrum, leaving me still guessing.

Knowing what I now know, I would aim for around 2 watts per gallon, using AHS light kits, in an enclosure similar to what AHS recommends on their website, and with that resulting fixture sitting on the tank. I would also realize that MH lights generally are available starting at 150 watts, so I would have little control over the watts per gallon, but I could always use those lights suspended above the tank far enough to limit the light intensity as I wished.
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Old 08-30-2008, 08:55 AM   #30 (permalink)
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Default Re: Proper Wattage for Aquariums

Color spectrum and lumens does not equate for plants. The majority of plants do not utilize green light for photosynthesis. A higher lumen rating at the same wattage often means greener light. Lumen is a rating weighted entirely towards human perception. It has little to do with the value of a light for either growing or viewing plants.

Lux is lumens/square meter, so they are similar. They are both defined in terms that are meaningful to human perception of light – not plants. They stress the amount of energy in the green band to which humans are most sensitive – not plants.

Artificial light sources are usually evaluated based on their lumen output. Lumen is a measure of flux, or how much light energy a light source emits (per unit time). The lumen measure does not include all the energy the source emits, but just the energy with wavelengths capable of affecting the human eye. Thus the lumen measure is defined in such a way as to be weighted by the (bright-adapted) human eye spectral sensitivity.

The standard measure that quantifies the energy available for photosynthesis is "Photosynthetic Active Radiation" (aka "Photosynthetic Available Radiation") or PAR. This is blue and red light. This is why it is so important to get the spectral output of a bulb before deciding if is a 'good plant light'.

Watts is also another term you need to be careful with. You can have 400 watts of lighting but if its not putting out light that plants can utilize its worthless. The bulb could have a relatively flat spectral output with little or no light usable by plants with very little intensity in the blue and red and a large green spike. So where are the watts going?>>>>>HEAT and an ugly green hue to your tank.
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