# Advancing the theory of MLT....



## Rex Grigg (Dec 10, 2002)

Ok gang. Here's your chance to beat up on me all the time. To make things easy I'm going to direct you to a thread on another board http://www.aquariumadvice.com/viewtopic.php?t=33308&start=10

Go down to my massive post.

Now hammer away at my theory of Minimum Light Threshold.


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## Rolo (Dec 10, 2003)

I completely agree. I just doesn't make sense to call your 5 gallon tank with a mere 15w (3 wpg) high light. It is only a mere 15 watts! Compare that to the 100, 200, 300+ watts people have on their larger tanks. 

I thought that was something very obvious that most in this hobby already understood. I'm surprised it isn't.


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## Ibn (Nov 19, 2003)

Interesting discussion going on there...

While I do agree with what's being said, I think that it's just a matter of definition - what's consider high to some and not to others. After years of being into the marine hobby (mini and microreefs), I don't really believe that you can go overboard in the lighting department. I've carried that same philosophy into planted tanks.

There's also so many variables other than lighting that effect the health and growth of plants (even though lighting is one of the largest bottleneck that there is).


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## putty (Nov 19, 2003)

Similar to my reactor crusade, but I gave up.

Good luck Rex, what you are saying makes total sense, but common sense is neither.


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## mpb (Jun 6, 2004)

I do agree. I think that what is really important is light intensity and light coverage. On smaller tanks even if you have 4 WPG you do not have a lot of light intensity. 
The WPG rule is just a rough measure. Things to consider are the tank area and tank height. Although they define the tank volume and they counterbalance each other area is more crucial than height. For example, consider the 20L and 20H tanks. Both tanks have the same volume but the 20L has more surface area. The 20L tank is taller but you do not need to make up for that as it is not over 18’’. The conclusion is that you need more light watts on the 20L.

So you can not always say that 3 WPG is moderate or high light On my 50 G tank I have now 3.4 WPG. Even when it had 3.1 WPG, the glosso was spreading like crazy. A plant that is known to be very light demanding.


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## Rex Grigg (Dec 10, 2002)

I have noticed that a lot of the tanks that are winning or placing high in various contests are running quite a bit of light. In the range of 5-8 wpg over 55-90 gallon tanks. Now that's a lot of light. But people are obtaining some excellent results with it. Of course there is not a lot of room for error there either. Here is one thing that more or less demonstrates what I mean. I have some purple Cabomba. Now when the LFS gets this plant in from the nursery it's very purple and the internode length is almost 0.  I can place this plant in my 4 wpg 55 gallon tank and within days the purple color fades and the internode length increases. Just for giggles this summer I took a couple of pieces and grew them in full sun outside. While the stock tank they were in developed a very nice GW bloom the Cabomba was nice and purple and the internode length was quite short. Now I was growing this plant outdoors above the 45th parallel. Not with the intense direct sun one would get in Florida where my LFS gets it. So to wind this up, the purple Cabomba will live and even grow at around 3-4 wpg, but to look it's best it needs a lot more light than that.

Ibn,

I think we all know that reef tanks can and do use HUGE amounts of light. Again I think the reason for this is you are keeping corals and such that have very high MLT. If you want that $100 rare coral frag to survive and grow you have to give it what it needs to survive. Lux over a coral reef close to the Equator can reach 140,000 or so at noon. That's a 140,000 lumens per square meter. A 55 watt PC bulb puts out 4600 lumens. So you would have to have 30 of those bulbs over a square meter of water to get to the 140,000 lumens that are naturally occurring. Now just as an example if one had a tank that was a meter cubed and wanted to duplicate the conditions found over that reef you would have to have around 1650 watts of light. And that would give you right around 6.33 wpg!!!! What a shock! This is actually the range that many people are running over reef tanks and what some people are having great luck with on plant tanks.

This same thing applies to FW plants. If one studies the Kasselmann book you will find that many of the plants we grow are found in very high light areas, light levels that we can't even begin to duplicate in the aquarium. So we are basically growing these plants in conditions that starve them of a vital nutrient. This is one reason I think that we do so much better with CO2 injection and having water column nutrient levels rarely seen in the wild. By making it extremely easy for the plant to obtain the other nutrients we are making up for the relative lack of light.

Light intensity might be a better way of measuring light over our tanks. Not watts per gallon but lumens per square foot or something like that.


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## Rex Grigg (Dec 10, 2002)

putty,

What reactor crusade? I'm always willing to join a crusade.


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## Ibn (Nov 19, 2003)

Rex,

I agree with you that WPG shouldn't be used in determining the amount of light since the intensity is more important. I've kept corals in the past (converted tanks over until I have the space and funds) and the planted tank is a segway within that sphere. I have found that there is a great amount of similarities in both ecosystems (e.g. your example for one), but with differing elements (calcium vs. nutrients). The one thing that has remained similar so far has been lighting. I'm running the same amount of lighting in my freshwater tanks as I was in saltwater, but this could be due to the fact that I'm just involved with small tanks (<40 gallon). 

Putty's reactor crusade has to do with the diagram that colin has up and the debate on whether the CO2 should be injected on the top or bottom of the reactor chamber...


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## putty (Nov 19, 2003)

Rex Grigg said:


> putty,
> 
> What reactor crusade? I'm always willing to join a crusade.


ahhh, well I plumbed my reactor with the CO2 coming in from the bottom, with the premise that the bubbles try to rise up and fight the current, and disolve, but everyone seems to be going the other way (CO2) coming in from the top. To me this makes no sense.

I am getting excellent CO2 levels in my tank using this method, and can clearly see bubbles rising in the reactor against the current. I have seen bubbles get caught up on the bio balls, until the completely dissolve. 

Apparently, this is not the way to do it though.

I think I am splitting hairs, but I do enjoy a good debate.


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## Ibn (Nov 19, 2003)

I stayed out of that debate, since mine is somewhere in the middleground and doesn't adhere fully to either of them.

To me, it really doesn't matter as long as I'm getting good results, which I am. To do so would just be pointless.


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## putty (Nov 19, 2003)

Me too. My way makes sense to me, and I am getting about 25 to 30 ppm of CO2 and some really happy plants.


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## Rex Grigg (Dec 10, 2002)

Well I bring the CO2 in at the top of the reactor but it is actually released about midway down the reactor. I think that you need to have the bubble fighting the current for best diffusion into the water column. 

I had a problem with a gravel vac reactor on my 29 gallon tank because I could not keep the bubbles in contact with the moving water long enough. I would soon end up with a huge bubble of CO2 at the top of the reactor. This was with DIY and pressurized. Once I built my external reactor my CO2 levels tripled with the same bubble rate.


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## putty (Nov 19, 2003)

Rex Grigg said:


> Well I bring the CO2 in at the top of the reactor but it is actually released about midway down the reactor. I think that you need to have the bubble fighting the current for best diffusion into the water column.
> 
> I had a problem with a gravel vac reactor on my 29 gallon tank because I could not keep the bubbles in contact with the moving water long enough. I would soon end up with a huge bubble of CO2 at the top of the reactor. This was with DIY and pressurized. Once I built my external reactor my CO2 levels tripled with the same bubble rate.


Thank you. I think people would be surprised about how much flow or force it actually takes to keep a good bubble down :tongue: 

Also because the reactor is much wider than the outflow pipe, the flow in it is much slower than in the tube. I thought that injecting at the top would cause a big bubble in the top of the reactor as you describe


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## Urkevitz (Jan 12, 2004)

I would love to put another 260 watt PC light on my 75 gallon. But I am afraid of what the electric bill would be. To me the tank looks extremely dim compared to the live coral tank at my LFS. Something to consider is in nature some plants grow in 20 feet plus feet deep water, maybe the intensity in deeper water is more on par with our tank lighting.


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## Ibn (Nov 19, 2003)

Perhaps. I'm tempted to slap the 4x96W (384W total) over the 40G when I'm redoing my parent's tank...


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## Rex Grigg (Dec 10, 2002)

Actually I don't think many of the plants we grow are found at depths of 20 feet. I know a few of them are but not many. This actually might be more a function of water clarity than anything else.


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## Urkevitz (Jan 12, 2004)

Yeah most places I find really deep plant growth is clear lakes. But when you think about it, our tanks are probably clearer than bodies of water the plants we grow are native to.


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## Rex Grigg (Dec 10, 2002)

I hope so. But when one looks at the pictures in the Kasselmann book you will see a LOT of shallow water.


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## bharada (Mar 5, 2004)

Rats! I though this thread was going to be about mutton, lettuce and tomato sandwiches...when the mutton is nice and lean, and the tomato is ripe...they're so perky. I love that. :tongue:

Sorry for the intrusion. Carry on, gentlemen. :icon_lol:


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## Rex Grigg (Dec 10, 2002)

Ok, I have added a page to my FAQ that may or may not help. If anyone wants to check it out (and if you do please check my math) go to www.rexgrigg.com/mlt.htm 

Please feel free to hack me to shreds if I'm wrong here. To summarize what is there I think that we should possibly go with Lux per Square Inch instead of Watts Per Gallon. I make my case on the new(?) page of my FAQ. Now I'm the first to admit that LSI still has it's flaws. Maybe we should go with LCI, Lux per Cubic Inch, but that's getting way out there on a limb. But if someone wants to do some math on it feel free to do so and share it with us. If you do so them please follow some of the examples I use on my page.

I now await the knives!


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## ninoboy (Jan 26, 2004)

This is my first time reading this thread. I totally agree with this method. Although wpg seem to be easier for people to use (you don't need to do the math and don't have to look for the small print on lux's number on the box). 

At least someone doesn't think I go overboard by using 72watts on my 10gl. I don't see that tank to be too bright and pretty much equal with my 4wpg 30gl tank which verify that your LSI seem to make more sense than wpg.

Good job man roud:


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## Laith (Jul 7, 2004)

The LSI method does seem to make more sense.

However, one of the issues with this method would be finding out what the lux of a specific lamp is : it's not always indicated!


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## Rex Grigg (Dec 10, 2002)

ninoboy,

If you were here and I was wired different I would kiss you. I have a 10 gallon tank with 43 watts over it. Nominally that gives 4.3 wpg. But I can tell you that higher light plants don't do well in that tank. If fact most stem plants lose the bottom leaves, elongate the internodal length and stretch for the surface as soon as they can. Then while growing right under the light they will almost grow like they should but still show signs of light deprivation.


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## Rolo (Dec 10, 2003)

This thread is making me reconsider my 40 gallon breeder's lighting. Probably now going to go with 2x96w for 4.8wpg.  



Rex Grigg said:


> I have noticed that a lot of the tanks that are winning or placing high in various contests are running quite a bit of light. In the range of 5-8 wpg over 55-90 gallon tanks. Now that's a lot of light. But people are obtaining some excellent results with it.


Ah, I'm so glad someone else has realized this! I've been going through a lot of aquarium journals, especially aquascapes and I'm killed by the amount of light they use. Only a few use under 3wpg on tanks that are 50, 100+ gallons. There was one I recall that was around 2, but he was using VHO which produces more light/watt then CF. 

That article in your page Rex is perfect. Gets straight to the point. All seems well to use Lux instead of watts, I'm for it, but finding the lux on every bulb presents a problem. But in line of the mega-watt tanks that use 5-8 wpg and still do excellently, seems we should just jack up the wpg rule?


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## Ibn (Nov 19, 2003)

ninoboy said:


> This is my first time reading this thread. I totally agree with this method. Although wpg seem to be easier for people to use (you don't need to do the math and don't have to look for the small print on lux's number on the box).
> 
> At least someone doesn't think I go overboard by using 72watts on my 10gl. I don't see that tank to be too bright and pretty much equal with my 4wpg 30gl tank which verify that your LSI seem to make more sense than wpg.
> 
> Good job man roud:



LOL, nice there nino. Running a similar setup on my 10G (actually around 7G with the beefed up substrate depth) right now with a similar amount of wattage.

Nice read and great job on that page (website for that matter) of yours! roud:


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## Rex Grigg (Dec 10, 2002)

I would be a bit hesitant about running 4.8 wpg over a 40 breeder. I will admit they are a pain to light due the the width and with how little height they have. You really have to have two fixtures on them if you run them length wise. I would really like to have the space and money to play with a 40 breeder. My idea of lighting it would be AH Supply 36 watt kits mounted front to back. I would use the single kits and maybe the double for the part of the tank I really wanted to blast the light into. But it would be an interesting lighting idea.


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## bharada (Mar 5, 2004)

I'm running 2x96w over my 40g breeder, but I'm using two, single bulb Aqualights. A 2x96 fixture has the bulbs too close together to get good front-to-back light spread.

Except for the hair algae growing on my driftwood (which actually looks kind of nice), I've never had any light related issues on this tank. The worst I've had were plants not liking my hard water.


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## jayc (Jul 8, 2004)

Rex, 

I think it would be a good idea to define the term "lux". Is that an abbreviation for lumens or is it something entirely different?

Jay


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## zapus (May 26, 2004)

Noun 1. lux - a unit of illumination equal to 1 lumen per square meter; 0.0929 foot candle


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## Rex Grigg (Dec 10, 2002)

Thanks zapus.


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## IUnknown (Feb 5, 2003)

Ok, just trying to understand things.


> Well find the surface area of your tank in square inches. Then take the LSI number you want to reach. Multiply the surface area by the LSI. Take the result and divide it by the LUX rating of your chosen light.


20 gallon high (24"x13"x16")
surface area=312 sqinches
want high light tank, so LSI of 30.
312x30=9360
lux rating of lights
2x55watt so 4600 lumesx2=9200
9360/9200=1.017
whats that number tell you?
Also, I'm actually running Metal Halide. The lumens on the bulb description is the following,


> aqualine 5000 is a metal halide lamp with a colour temperature of 5000° Kelvin - daylight
> This lamp was specially developed for the illumination of freshwater aquaria having a high percentage of red light and a high intensity - 11000 lumens per watt. It gives planted aquaria a natural appearance and enhances plant growth.


so the 70 watt MH is more intense than the two 55w AH bulbs? 11000 compared to 9200? Why does it say 11000 lumens per watt? Does that mean 70 x 11000 lumens?


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## Rex Grigg (Dec 10, 2002)

You missed one thing. You should take the LUX rating of a single bulb. Then the number will tell you how many bulbs you need. In your case it's telling you that you would want 2 bulbs. But with the AH Supply reflectors you can get by with the 2x36 watt kit.


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## BSS (Sep 24, 2004)

Oh, so now you're going to add in the quality of the reflector variable  . That's just gonna add confusion.

Sounds like a very good approach. I like it! Should there be some parameters added in regards to the depth of the tank? Say, something like, this approach works for tanks < NN" deep? Or will it cover most 'standard' tank sizes. Just a thought...

Brian.


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## Rex Grigg (Dec 10, 2002)

Well reflectors make a huge difference. The WPG rule was formed when NO tubes with basically no reflectors. So when you put a good reflector over the bulb you are actually getting a lot more usable light into the tank.

I figure that when the WPG rule was laid down most lighting setups were at most 40-50 efficient. Now with reflectors such as the AH Supply ones I would say those are at around 85% efficient. That makes a HUGE difference.


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## GulfCoastAquarian (Jul 30, 2002)

I commend your efforts, Rex. While the wpg rule works well enough for most popular tank sizes, it obviously diverges as tank size gets increasingly small or large. I agree we need something new, for advanced hobbyists to help diagnose light intensities versus plant growth.
Firstly, I'd like to address the maximum light intensity found in the tropics. 140k lux at noon is indeed common, but that value drops off rapidly as the sun's angle decreases. So you're only seeing intensities >100k lux for a few hours a day. Luckily for us, plants are able to adapt to less intense lighting, for longer periods. Would plants be more healthy with only short periods of fantastically intense light, surrounded by a longer period of more moderate lighting levels? You'd certainly think so. One of the best ways to care for any plant or animal is to mimick nature. That's why a lot of us with high light levels don't bring on all the lights at once. Aside from shocking the fish, the plants are unable to utilize that light for some time so it makes sense to bring the tank up to 1-2wpg, and then full 3-4wpg for midday intensities.

But let's go ahead and get away from watts per gallon. Lighting technology is changing and the relative lumens/watt output of bulbs is so diverse that I believe the wpg rule will become completely unuseable in the near future.
I'm not sure why you chose Lux per Sq In (LSI), though. Lux is already a measure of illumination density (lumens per sq meter). If you wanted to provide a method to calculate illumination density, users could use the rated mean lumens output of a bulb and divide it by the floor surface of their aquarium.
For example, the infamous 55g aquarium (approx 48" x 12" x 21") and the ever popular four F40T12 normal output fluorescent bulb configuration.
You've got 578 sq in of floor surface area (48" x 12")
You've generally got approx 2000 lumens (mean) per 40w bulb for a total of 8000 lumens.
So 8000/578=13.9 lumens/sq in
Multiply by 1550 to convert from _lumens/in^2_ to _lumens/m^2_ and you get:
~21,500 _lumens/m^2_ (or lux). That's about 15% of the intensity of noonday tropic sunlight. We also know that this 55g tank, with 2.9wpg, is a pretty popular setup and can grow a large variety of plants needing moderate lighting levels. So we can call this a tank with _medium_ lighting levels.

All that sounds good, and I wish we could just leave it at that, but there are a few more items to consider that make this MLT calculation a bit more confusing...


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## GulfCoastAquarian (Jul 30, 2002)

*Reflectors*
Most shop lights have plain white sheet metal reflectors that direct 55%-65% of the bulb's output to the aquarium surface, at best. A decent polished aluminum reflector might bump that to the 65%-75% range. A specular aluminum reflector, such as the MIRO-4 reflector included in the AHsupply kits, will push those efficiencies up to 85%, as it has been mentioned. 
To make up for this, we could come up with a few different classes of reflectors. 
Category 1 would be white reflectors (painted wood, sheet metal, etc.)
Category 2 would be polished reflectors (but non-specular aluminum)
Category 3 would be Specular Al Polished reflectors. Just to refresh your memory, specular aluminum is cast differently that regular sheet aluminum with far less porosity and is designed for maximum reflectivity. 
As for the efficiency ratings for each category, it varies, but the aforementioned 55%-65% for Cat1, 65%-75% for Cat2 and 85% for Cat3 are probably close enough.

*Tank Depth*
There have been several discussions on tank depth and absorption of light. We've even discussed the various wavelengths of light and how they are absorbed at different rates due to the density of the water, etc.
Bottom Line - for most popular tanks less than 2-3 feet tall, tank depth does not affect illumination density enough to bother considering it in something that is meant to be just a guideline. Obviously, you'll need to go to the top end of the light intensity range in order to grow foreground plants that require intense light. And conversely, you might be able to grow tall stem plants that require intense light in a medium-lit tank since they will be closer to the source.

*Lumens*
Here's the problem. Lumens does not measure the energy from _all_ wavelengths being emitted from a light bulb. Only the ones capable of being seen with the human eye. Why does that matter? Because you could have two bulbs with exactly the same lumens output, and one bulb's output could be focused on the wavelengths _humans_ see, while the other bulb's output could be focused on the wavelengths _plants_ see. 
So if you're using a general purpose daylight bulb that's putting out 2000 lumens, but it is all centered around the wavelengths that humans see (photopic curve), the plant could still theoretically "starve for light". Now, this is rarely the case since most daylight bulbs provide a good balance of light in all visible wavelengths, but it still makes it pretty hard to tell just how many of the lumens the bulb is putting out are being used by the plants.
There's an extensive thread talking about this topic on this site. Grab a pot of coffee and read through it...
Lumens and PAR

Bottom line - I still think the lumens/in^2 guide is better than the wpg rule. Regardless of the spectral output of the bulb. If we could pioneer a guideline and prove that it works, we could accomplish something. Many have tried, but that doesn't mean it is not possible.


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## Rex Grigg (Dec 10, 2002)

Good points Sam. I posted this to get more heads thinking about it. But I do really question if a shop light reflector gets anywhere close to 55-65% of the light into a tank. I wish I had a light meter to check that with. I would think that you would actually get no more than 40% at best.

I picked LUX instead of Lumen because LUX is a measurement of total light. And in the Kasselmann book she gives light readings in LUX.


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## GulfCoastAquarian (Jul 30, 2002)

Rex Grigg said:


> Good points Sam. I posted this to get more heads thinking about it. But I do really question if a shop light reflector gets anywhere close to 55-65% of the light into a tank. I wish I had a light meter to check that with. I would think that you would actually get no more than 40% at best.
> 
> I picked LUX instead of Lumen because LUX is a measurement of total light. And in the Kasselmann book she gives light readings in LUX.


You might be right about the shop light (or any painted white) reflector. And I sure do wish someone had a luminosity meter to validate that!

Lux is a good measure, but it is already a measure of illumination density (energy per unit area) so we could just use it, instead of lux per sq in. (which would result in units of energy per area squared). Most bulbs are rated in lumens, anyway.

Did a quick calculation on my 55g tank. Four 55w PC bulbs (5000 lumens each).

5000 lumen x 4 bulbs = 20k total lumens
20k lumens / 578 sq in floor area = 34.6 lumens/in^2
Multiply by 1550 to convert to 'per m^2' -> 53,633 lumens/m^2
Ends up around 53k lux, or 38% noonday tropics.
But then take reflectors into consideration...
I've got specular aluminum reflectors over only half the bulbs. Regular polished aluminum over the other half. So 85% for one half and 75% for the other half reduces that number to about 42,900 lux, or 30% noonday tropics.


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## aquaverde (Apr 15, 2003)

On tank depth-
I think it’s not an issue per se, unless you have severe turbidity, which is an unrelated issue that needs correcting, not one that would be constant. I started with a tank that is deeper than it is long (24” depth), and the real issue IME is shading. Another difference in a deep tank would be light coverage, since there’s more reflected back into the tank from the glass.

Lumens
I think an exercise to replace the wpg rule will have to assume the use of daylight or wide spectrum light sources. One reason wpg hasn’t been trashed up to now is that plants are capable of adapting to a pretty wide range, so we squeak by with that kind of latitude. Studies of individual bulbs and their PAR would make useful supplements to the new rule- but only supplements. The advantage of using lumens is that it is THE available light output measure.

Direct measurement of the light output with the 3 categories of reflectors mentioned would require more equipment than most of us can*not* get access to. It would be great if someone who could, would do this sort of thing. That person would have to do it all to maintain comparative consistency in the measurements. I’m still going to do some ODNO measurements on NO 36” bulbs. I got a (relatively!) cheap meter to try to do it with. $75 for the bargain basement model, and I’m not sure how it will work due to its limited range.

Glad Rex started this. I'm posting as much to keep the discussion going as to state my thoughts. Hope it continues.


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## Rex Grigg (Dec 10, 2002)

The more I think about it the more I feel that if you can get to that 30-40% of the tropical noon sunlight you should be able to grow just about anything you want. I will have to play around with the figures and see what kind of lighting levels that gives for some of the smaller tank sizes.


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