lighting theory - very long post!

[cellodaisy]

This whole "watts per gallon" thing wasn't making sense to me. I mean, we all know that fluorescent bulbs are more efficient than regular incandescent bulbs, so how could there be a blanket "watts per gallon" rule when different kinds of bulbs would put out different amounts of light for the same wattage? So I went researching. (Big thanks to Nolapete and TwoTankAmin for pointing me in the right direction.)

DISCLAIMER: I'm a total newbie to all of this. I think I get the theory, but I have no experience to back it up. I am NOT trying to tell ANYONE what to do, I'm just hoping to get feedback on this so I'll know if I'm on the right track or if I've got it totally wrong. Now back to our regularly scheduled programming. Here goes nuthin'.

First some definitions as they pertain to aquarium lighting:

watts - the rate at which a bulb consumes energy
lumens - a measurement of the amount of light output
lux - a measurement of light over a given area (1 lux = 1 lumen per square meter); 1 lumen over 1 square meter is a lot different from 1 lumen over 100 square meters---it matters how "thin" the light is spread
lumens/watt - the amount of light that a bulb puts out per watt (the bulb's efficiency)

Different bulbs have different lumens/watt. That's why you see things like "60 watt equivalent" on a compact fluorescent bulb, even though it consumes far less than 60 watts. Because it is more efficient (has a higher lumens/watt output), you can get more light for the same wattage OR the same light for less wattage.

For example, let's say we have a typical incandescent (regular) light bulb that gets 10 lumens/watt and a much more efficient compact fluorescent that gets 40 lumens/watt. Let's say they're both 100 watt bulbs.

incandescent: 100 watts x 10 lumens/watt = 1000 lumens
fluorescent: 100 watts x 40 lumens/watt = 4000 lumens

But what if you only wanted 1000 lumens, but you wanted to switch to a fluorescent to save electricity?

(1000 lumens)/(40 lumens/watt) = 25 watts

That's why, in our scenario, a 25 watt fluorescent would give us the same light as a 100 watt incandescent. (Note: Lumens/watt depends on a lot of factors and each bulb is different. I just chose plausible numbers that were easy to work with.)

You can see that with the myriad different kinds of bulbs available now with widely varying efficiencies, a "watts per gallon" rule doesn't work. Your tank doesn't care how much electricity you use, it cares how much light it gets.

So if we assume that the old rule works for mid-sized tanks (and I think that's not a bad assumption since so many people still use it and their tanks do quite well), let's use a 55g as an example. By the old rule, "low light" is 2WPG, so a 55g would require 110 watts. Most people use fluorescents, so we're assuming this rule means 110 watts of fluorescent light, and we'll just go with an average efficiency for fluorescent tubes (different tubes will have different efficiencies).

Rex over at rexgrigg.com discusses this. He dismisses tank depth as irrelevant and I'm just going along with that. You should really go visit because he has some great things to say on other topics as well. (I just have to note, because I'm anal about things like this, that Rex uses the terms watts, lumens, and lux very loosely, so you won't find them used the same way in my write up. Who am I to question more experienced fishkeepers? I dunno. Nobody, I guess. Please feel free to ignore everything in this post! :))

On to our 55g/110w example:

55g surface area = 48in x 13in, or about 0.4 sq.meters

fluorescent lumens/watt = 50 (conservative estimate)
light output of 110 watt (fluorescent) = 5500 lumens
5500 lumens/0.4 sq.meters = 13750 lux

So if we use the old 2WPG rule and 55g/110w as a starting point, we get a new low-light rule of 13750 lux. (We did a lot of estimating to get this number, so it's a rough guide only.)

To calculate the your low-light wattage needs by this new rule:

1) Find the surface area of your tank and convert it to square meters
2) Multiply your surface area by 13750 to get the number of lumens you need.
3) Find the lumens/watt rating of the lighting you want to use. (Keep in mind that the housing/reflector will impact the ultimate lumens/watt efficiency.)
4) Divide your required lumens by the lumens/watt rating of your lighting type. Voila! You have your wattage requirement according to the new rule.


Example: I have a 10g that I want to set up for low light.

1) 10g surface area = 20in x 10in
20in x 10in = 200sq.in
200sq.in = 0.129sq.meters
2) (0.129sq.meters)x(13750 lumens/sq.meter) = 1774 lumens
3) We'll use our 50 lumens/watt estimate for now.
4) (1774 lumens)/(50 lumens/watt) = 35 watts

So you see we end up with 35 watts, where the old rule would say 20 watts.

So my question to all of YOU more experienced fishkeepers is this: does it work? I can't find any problems with the theory, but I have no experience to back it up.

Comments, criticisms, etc. all welcome. Thanks for reading!

[jpappy789]

One thing that bothers me is that lux is a measurement based on the human eye, therefore lumens are as well...can someone explain how that corresponds to the amount of lighting needed for plants? It seems like you could easily just insert foot candles in instead, although it would be obvious that any measurement in foot candles would be utterly useless...

[cellodaisy]

One thing that bothers me is that lux is a measurement based on the human eye, therefore lumens are as well...can someone explain how that corresponds to the amount of lighting needed for plants? It seems like you could easily just insert foot candles in instead, although it would be obvious that any measurement in foot candles would be utterly useless...
Yes, I thought about that, especially since human eyes are more sensitive to green, which is almost useless to plants. I'm not quite sure how to do it, but I know I need to work color temperature (degrees Kelvin) into my calculations somehow. I'd love your suggestions for doing it!

[jpappy789]

Haha I wish I could help but unfortunately you'd need to turn to the heavy duty plant experts (Rex Grigg, Tom Barr etc.) for that answer...unless another AC member has a suggestion?

[jmhart]

So,

All of your concerns about the watts per gallon "rule" are accurate. There are many flaws with calling it a "rule", that's why I like to refer to it as a guideline. There are many exceptions to the rule, for example:

1)"Rule" was developed for NO T12 bulbs, so all other bulbs fall outside the rule. That's where this comes in handy:http://www.plantedtank.net/articles/Light-Bulb-Comparison/29/

2)"Rule" doesn't apply to tanks smaller than 20g or larger than about 80g. Read this: http://www.rexgrigg.com/mlt.html

3)Lumens is indeed a slightly more appropriate view of light, but PAR is an even more appropriate measurement. Unfortunately, most manufacturers do not yet provide PAR values for bulbs, so you'll have to rely on fellow hobbyist to supply this information.


So, to wrap up, your thinking is correct. You put a lot of thought into, perhaps more than required, but you arrived at the same conclusion that many people before you have arrived at.


One more thing to add: This website broke down light over dozens of Amano tanks, and performed a mathematical analysis, resulting in a nice formula that would indicate, perhaps, what Amano would, or has, used over tanks of particular size: http://www.fitchfamily.com/lighting.html

[jpappy789]

I feel dumb...what does PAR stand for again?

[jmhart]

PAR=Photosynthetically Active Radiation

[jpappy789]

Thanks! :thumbsup:

[cellodaisy]

Maybe if I figure out more specifically how lumens are measured, there could be some kind of conversion from lumens to total energy output?

[jpappy789]

But I still think there is a gray area that encompasses what our lights give out and what our plants actually need to take in...

[cellodaisy]

Sorry jmhart---posting at the same time and didn't see your comment about PAR. Thanks for the links---I'll check them out!

[jmhart]

Jpappy is right, lumens are not an accurate measurement. Lumens does not reflect how much energy is available for the plants, because as lumens are measured, they apply to how the human eye senses and uses light.

PAR is what you are looking for, not lumens.

[cellodaisy]

But I still think there is a gray area that encompasses what our lights give out and what our plants actually need to take in...

... and I'm sure different plants have different needs. Any "rule" would be approximate, I just can't help thinking that there has to be something more accurate than WPG.

[jmhart]

:wall:

[cellodaisy]

:wall:

My sentiments exactly! :crazy:

[jmhart]

What is PAR? (http://www.google.com/search?hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&hs=h2h&q=PAR+aquarium&btnG=Search)

[AshK]

So,

2)"Rule" doesn't apply to tanks smaller than 20g or larger than about 80g. Read this: http://www.rexgrigg.com/mlt.html


Rex Grigg's LIS theory is complete garbage. If you check his math or try to follow his logic/calculation methods you will get results no where close what he says. I think us hobbyists need to band together and re-educate him. He seems to be confusing Lux and Lumens.

While most of can agree watts aren't that great for creating rules with, even creating a rule with lumens has some problems too. And with any rule, reflectors are rarely taken into consideration. A compact fluorescent bulb of 23 watts may put out 1600 lumens, but with the considerable restrike and lack of suitable reflectors, way less is getting into the tank/to the plants.

To refine your theory I would channel it in the direction of Rex Grigg, but do it correctly. Your lumens/watt idea is kind of the same as the old rule, just a little refined. Check out this page for a different approach(shown to me by MG):

http://woo.gotdns.com/Aquarium/Lighting.htm

It talks about lumens per square inch of surface area. I consider it to be slightly better than the WPG rule, but definitly not the end-all-best-rule-of-awesome.

[jmhart]

While most of can agree watts aren't that great for creating rules with, even creating a rule with lumens has some problems too. And with any rule, reflectors are rarely taken into consideration. A compact fluorescent bulb of 23 watts may put out 1600 lumens, but with the considerable restrike and lack of suitable reflectors, way less is getting into the tank/to the plants.



Any rule developed for bulb/power output should be independent of reflectors. Reflectors are different across the board, and require their own separate review. Using a guideline, like wpg, should be used in conjunction with the best reflectors possible.

[cellodaisy]

Rex Grigg's LIS theory is complete garbage. If you check his math or try to follow his logic/calculation methods you will get results no where close what he says. I think us hobbyists need to band together and re-educate him. He seems to be confusing Lux and Lumens.

Yes, I did try (and, of course, fail) to follow Rex's mathematics and his use of the terms lux and lumen, but it got me started it this direction so I needed to give credit where it's due.

While most of can agree watts aren't that great for creating rules with, even creating a rule with lumens has some problems too. And with any rule, reflectors are rarely taken into consideration. A compact fluorescent bulb of 23 watts may put out 1600 lumens, but with the considerable restrike and lack of suitable reflectors, way less is getting into the tank/to the plants.

I also mentioned that reflectors will affect lumens/watt. Perhaps I should have been more clear, but I meant to communicated that the manufacturer's stated lumens/watt will be higher than your actual real-life lumens/watt, especially since we are only counting the light that stays in the tank.

To refine your theory I would channel it in the direction of Rex Grigg, but do it correctly. Your lumens/watt idea is kind of the same as the old rule, just a little refined.

I believe there are two significant differences between what I outlined and the old rule. (1) It takes into account the different efficiencies of different bulbs and (2) it uses surface area instead of volume, though I'm not sure of the value of that and am just taking Rex's word for it.

Check out this page for a different approach(shown to me by MG):

http://woo.gotdns.com/Aquarium/Lighting.htm

This appears to be exactly the same method I outlined. Am I missing something?

Thanks for your feedback!

[AshK]

LOL i read over your theory too quickly. As soon as I saw "Rex Grigg" I got thrown into a rage. I really absolutely despise that web page. So many people consider it the coolest thing since sliced bread.....and it doesnt even work. Sorry for my behavior.

But yes, now that I actually read your entire post I give you 2 thumbs up:thm::thm:. Now to work on something involving PAR LOL.

[cellodaisy]

LOL i read over your theory too quickly. As soon as I saw "Rex Grigg" I got thrown into a rage. I really absolutely despise that web page. So many people consider it the coolest thing since sliced bread.....and it doesnt even work. Sorry for my behavior.

No problem. Fuzzy math makes me mad, too.

But yes, now that I actually read your entire post I give you 2 thumbs up:thm::thm:. Now to work on something involving PAR LOL.

Thanks! PAR is indeed the next goal. My gut says there has to be some way to take a bulb's stated lumens/watt and *K and come up with something useful... not PAR per se, but a translation of lumens/watt into something that isn't centered on what the human eye perceives. Haven't worked it out yet...

...and seeing as I have to be bright-eyed and bushy-tailed at work in the morning, I should really put this aside for now and go to bed. But you haven't seen the last of me. I'm like a dog with a bone when it comes to stuff like this!

[Cory Keeper]

Yeah, I myself have issues with Rex, He may be a cool guy to be around, but sometimes he does come off a bit "fruity as a fruitcake". What irritates me most about Rex is that he seems to think that his way is the only way, and his followers follow blindly without question. His lighting theory is also off, by several factors. His rant about deep tanks and lighting is one. Don't care how well you slice it, deep tanks will have PAR issues unless you throw a ton of light over it. A difference of 12" in depth IS going to lower your PAR levels at the bottom. Even MH and LED will struggle past 24" depth.

And You really can't translate Lumens to PAR, Because while lumen is heavily weighted in the green, PAR is weighted in the blues and reds (where the human eye has a hard time seeing). No matter how well you try, it just doesn't translate.

But I am glad that someone here sees the big flaw with the WPG "guideline", whereas some on this forum (and others) think there is no alternative, or have failed to grasp basic electricity principles (I.E. Watts is not light). Though I have come up with an LED guideline for a planted tank, it is again, far from perfect and really depends on how tall your tank is. And I have added a disclaimer hoping people will not take it and run with it too much when better LEDs come about.

[jpappy789]

Just read over Rex Grigg's articles...never noticed the errors until now. :wall:

[Ace25]

Accidently stumbed in here by mistake from the SW area, but just had to chime in and agree what others have said..

PAR is the ONLY measurement you should look for when dealing with photosynthetic species, whether it be plants or corals. PAR is the only meaningful measurement for them, all other measurements like Lumens and Lux only pertain to how the human eye interprets the light they are visually seeing. To me, the WPG rule went out the window last century. ;)

To get a PAR reading you need a PAR/PPFD meter and you check multiple locations underwater to get the different PAR values. PAR varies greatly at different locations underwater. It will be the highest reading at the surface of the water directly under the bulb, and taper off as you move away.

[phanmc]

Thanks! PAR is indeed the next goal. My gut says there has to be some way to take a bulb's stated lumens/watt and *K and come up with something useful... not PAR per se, but a translation of lumens/watt into something that isn't centered on what the human eye perceives. Haven't worked it out yet...

I don't think that will be possible. Take a look at the following light bulb comparisons:

http://www.aquabotanic.com/lightcompare.htm

Note two bulbs: ADV850 (Philips Advantage fluorescent, 5000K F32T8/ADV850) & TL950 (Philips TL950 5000K fluorescent very high CRI (98) F32T8/TL950)

The two bulbs have almost identical specs (32w, 5000k, T8s, same manufacturer) yet the first one is one of the most efficient in terms of PAR while the other (with the higher lumens and CRI) is one of the worst. So that rules out using lumens and k ratings as an effective proxy for PAR.

[KarlTh]

Once misconception about deep tanks does need addressing - the idea that certain types of light can "punch down" through the water column better than others. OK, some light frequencies are scattered more than others through the water, but there seems to be an idea that there's some kind of "punching power" quite independent of intensity. The way some people talk you'd imagine that some light hits the water and gives up, whilst other kinds of light go flying past much faster and straight through. Einstein's corpse must spin in its grave.

[cellodaisy]

You really can't translate Lumens to PAR, Because while lumen is heavily weighted in the green, PAR is weighted in the blues and reds (where the human eye has a hard time seeing).

PAR is the ONLY measurement you should look for when dealing with photosynthetic species, whether it be plants or corals. PAR is the only meaningful measurement for them, all other measurements like Lumens and Lux only pertain to how the human eye interprets the light they are visually seeing.

I don't think that will be possible. Take a look at the following light bulb comparisons: http://www.aquabotanic.com/lightcompare.htm

You are all right. As I was lying awake in bed thinking about this stuff, I realized that the stated color temperature (K) of a fluorescent is a weighted average of the K emitted by each of its phosphors. That's why bulbs with the same K and lumens/watt could have different PAR---they have different mixes of phosphors. :wall:

OK, some light frequencies are scattered more than others through the water, but there seems to be an idea that there's some kind of "punching power" quite independent of intensity.

Hmmm... if certain wavelengths are more scattered, wouldn't they "punch down" less? And wouldn't it then stand to reason that light emitted at a wavelength that doesn't scatter as much in water would "punch down" more? I know that blue gets more scattered, but some resources seem to indicate that red passes through and others indicate that it is absorbed by the water (and turned into heat). :help:

I really have to get some work done now. Waaaay too much loafing off at AC during the work day recently. :o

[KarlTh]

Yeah, there would be some difference, but I doubt it's significant over the wavelengths available to us in aquarium lighting.

[PuppyFluffer]

Very interesting conversation!

This is totally off topic but chime in if you have any thoughts please:
http://www.aquariacentral.com/forums/showthread.php?p=1806400#post1806400

[Star_Rider]

I believe the longer wave length is scattered,absorbed more(red,yellow,orange,)
while shorter wave lengths can penetrate deeper(violet,blue,green)
much of the visible light is absorbed/scattered in the first 33' the surface turbulence also comes into play as light is also reflected off the surface.

(random scattered thoughts);)

[jmhart]

You are all right. As I was lying awake in bed thinking about this stuff, I realized that the stated color temperature (K) of a fluorescent is a weighted average of the K emitted by each of its phosphors. That's why bulbs with the same K and lumens/watt could have different PAR---they have different mixes of phosphors. :wall:



Hmmm... if certain wavelengths are more scattered, wouldn't they "punch down" less? And wouldn't it then stand to reason that light emitted at a wavelength that doesn't scatter as much in water would "punch down" more? I know that blue gets more scattered, but some resources seem to indicate that red passes through and others indicate that it is absorbed by the water (and turned into heat). :help:

I really have to get some work done now. Waaaay too much loafing off at AC during the work day recently. :o

Yeah, there would be some difference, but I doubt it's significant over the wavelengths available to us in aquarium lighting.

Karl, if you were responding to cellodaisy's post above, then I want to note that the difference is extremely significant. If you were responding to something else, then ignore this.

Cellodaisy, kelvin ratings of bulbs are more-or-less an average of their spectrum. There's also a differences in how manufacturers rate bulbs. Some manufacturers are fairly reliable in indicating a percieved kelvin value for the light produced by their bulb.

To better understand, it's important to understand what a kelvin rating actually is. When carbon is heated to a certain temperature(say 6700 K) the light eminating(the wavelength) from that carbon is said to be 6700 K. Make sense?

So, how this applies to some manufacturers is that they say a bulb produces 6700k. Is that the entire wavelength produced by the bulb? No, but it's an approximatation of the color....meaning the color produced would be similar to if you heated carbon up to 6700K.

So, that system makes since.

Some other manufacturers, seemingly, just pick arbitrary values that really don't seem to mean anything.

Anyway, how this all relates to what Karl said, is that it does seem to be an average of the spectrum produced. I wish I could find a decent example(maybe somebody can help), but....There are dozens(if not hundreds) of 10,000k bulbs on the market. Next time you are around a good selection, pick up a couple of "10,000K" bulbs and compare the spectrum provided on the package. The spectrum is really quite different, despite all being 10,000K.

[jmhart]

I believe the longer wave length is scattered,absorbed more(red,yellow,orange,)
while shorter wave lengths can penetrate deeper(violet,blue,green)
much of the visible light is absorbed/scattered in the first 33' the surface turbulence also comes into play as light is also reflected off the surface.

(random scattered thoughts);)


That's right. That's why a lot of dive lights appear very red when used on the surface, because down underwater there is still a lot of blue to be used.

Also relevant to a discussion about why SW need actinic lighting

[jmhart]

For an interesting read on PAR, check out:

http://www.efn.org/~k_mccree/Professional/PAR.html

[cellodaisy]

Kelvin ratings of bulbs are more-or-less an average of their spectrum. There's also a differences in how manufacturers rate bulbs. Some manufacturers are fairly reliable in indicating a percieved kelvin value for the light produced by their bulb.

To better understand, it's important to understand what a kelvin rating actually is.

I do understand Kelvin ratings---what I had failed to take into account initially is that fluorescents use different combinations of phosphors and that each one will emit its own little piece of the spectrum and have its own average Kelving rating, and that the reported Kelvin rating of a bulb is an average of the averages. To totally oversimplify, the average of 1 and 5 is the same as the average of 2 and 4, but if plants are only sensitive to 1 and 5 then then the bulb producing 2 and 4 is useless, even though it has the same average.

A lumen is a measurement of light adjusted for human perception. If you took a bulb's stated lumen output and unadjusted it, you would be left with something closer to its total light energy output. If you could then figure out how much of that light was coming from each type of phosphor, and therefore how much light was emitted at each K rating, you might have some useful information. Sounds awfully complicated, though. Much easier to just get PAR ratings from a meter or fellow hobbiests!

For an interesting read on PAR, check out:

http://www.efn.org/~k_mccree/Professional/PAR.html (http://www.efn.org/%7Ek_mccree/Professional/PAR.html)

Great link! Looking forward to reading it after work.

I'm still confused about the whole wavelength scattering thing. I found this site that explains (in very simple terms and cartoons) why the sky is blue---because the blue light gets scattered everywhere and the red light gets through: http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html. Wouldn't water be the same?

[SuBXeRo]

my head hurts :( too much speculation for me. here is what i dont get. everything below is me just using common sense and my basic knowledge of the subject.

plants need radiation (light) to photosynthesize to grow. Radiation outside of light would be harmful and useless to plants as those would include microwaves, radiowaves, gamma rays, etc. SO we are talking about the light spectrum specifically.

If we have two bulbs that are flurescents with exact same specs but different gas mixtures, you are essentially emitting the same color (kelvins) with the same efficiency. so that means that the gas mixtures differences would have to emit radiation in different wavelengths for their PAR's to be higher because plants need higher PAR values to propagate better. In emitting wavelengths in different quantities you would change the color of the bulb because of a greater intensity in that spectrum.

now i can see this being true if our eyes are not sensitive enough to notice the change. i assume that kelvins are based on what the average human can see but that would have to be based on mathematical equations for the reproduction of these tempewrature ratings on bulbs. with a mathematical background, differences in color would be detected by the math and not our eyes and bulbs should be labeled as such. The important waves used by plants can be seen by the human eye so we should not be worrying about the outlying wavelengths.

does this make any sense? there has to be a relation between color temp (k) and pars because once u change color you change the dominant wavelength which would affect PAR.

[jameshilljr]

:crazy: I guess I'm just one of the followers-I'm just glad my plants are growing fine with the lighting I have... Ya'll have put alot of research and thought into this one...very interesting read

[Nolapete]

Ashk, just because you don't understand Rex's theory doesn't make it garbage. It actually makes a lot of sense if you read it in the context outside of the WPG "rule" which so many people are duped by.

WPG is total idiocy just like inch per gallon for stocking is. There are far too many variables involved to have one set way of gauging how many watts of what temperature light you need for every aquarium.

The best practice is to either go with 1.5 wpg for low-mid light and 2.5 wpg for mid-high light plants and watch how they grow. Let the plants be the guide for the amount of light. All things equal, if they aren't growing the way you expect them to then you need to increase the amount of light that actually gets to the plants.

If you've read any of what Rex has written, that statement is the core of what he says about lighting. You could have 5 wpg and have horrible growth if the light is out in the room and not getting to your plants. 2.5 wpg with quality reflectors that direct the light into the tank is going to be more effective than more light without them.

[Nolapete]

I'm still confused about the whole wavelength scattering thing. I found this site that explains (in very simple terms and cartoons) why the sky is blue---because the blue light gets scattered everywhere and the red light gets through: http://math.ucr.edu/home/baez/physic.../blue_sky.html (http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html). Wouldn't water be the same?

Water acts as a prism, so not really the same. You can see it working the same way the sky does in the ocean though. The deeper you go the less the spectrum is able to penetrate. The blue scattered light is all that can make it through.

[AshK]

Ashk, just because you don't understand Rex's theory doesn't make it garbage. It actually makes a lot of sense if you read it in the context outside of the WPG "rule" which so many people are duped by.


Wow, please don't bring your perceptions of my intellegence in to this conversation. It is clear that I--and almost all the people in this thread excluding you--find his logic, math, and general theory to be fuzzy and in need of serious reformation. If all the people on this forum did 3 seconds of wikipedia research and then read Rex's LIS theory, they would surely consider it garbage as well. I challenge you to follow his exact method and post your results here. Try to apply his rules to your tanks.

[cellodaisy]

If we have two bulbs that are flurescents with exact same specs but different gas mixtures, you are essentially emitting the same color (kelvins) with the same efficiency. so that means that the gas mixtures differences would have to emit radiation in different wavelengths for their PAR's to be higher because plants need higher PAR values to propagate better. In emitting wavelengths in different quantities you would change the color of the bulb because of a greater intensity in that spectrum.

Fluorescents don't get their colors from gases; they get them from phosphors. Phosphors are materials that coat the inside of the tube. Without phosphors, fluorescent bulbs would emit UV radiation. Phosphors absorb that UV and emit light in the visible spectrum.

Two bulbs could have the same average K rating, but have different phosphors. One analogy would be colored sand. If you mixed red sand and blue sand, it would look purple, but you don't actually have purple colored sand. So I could take one bucket and mix 50% red sand and 50% blue sand, and in another bucket mix 70% reddish-purple sand and 30% blue sand, and both could look straight purple, but they actually have different colors of sand.

i assume that kelvins are based on what the average human can see

I don't think Kelvin ratings are based on human perception, but I could be wrong.

The important waves used by plants can be seen by the human eye so we should not be worrying about the outlying wavelengths.

Yes, the light plants need is in the visible spectrum, but plants are more sensitive to red and blue light, while human eyes are more sensitive to green. This is why lumens are a problematic measurement of light output, because lumens are weighted according to human eye sensitivity (i.e. a green light would have a higher lumen rating than a red light putting out exactly the same amount of energy).

there has to be a relation between color temp (k) and pars because once u change color you change the dominant wavelength which would affect PAR.

There is a relationship, but in the case of fluorescents we only have the average K rating and we don't know what components when into that average. In our sand bucket analogy, both buckets would have a "K rating" of "purple," but neither bucket actually has any purple sand in it and if we didn't know what colors of sand went into it we would have no way of finding out just from the K rating.


Water acts as a prism, so not really the same. You can see it working the same way the sky does in the ocean though. The deeper you go the less the spectrum is able to penetrate. The blue scattered light is all that can make it through.

I found a fantastic explanation at http://www.serc.si.edu/labs/phytoplankton/primer/hydrops.jsp. About halfway down the page, under "Absorbtion," it says:

The intensity with which a substance absorbs light depends on the wavelength of the light. It is the wavelengths that penetrate deepest that determine the color of the water. For example, water molecules selectively absorb energy from lower energy wavebands in the reds, yellows and greens, leaving only blue light. Therefore very pure and deep waters appear blue.So some wavelengths (specifically blue) do "punch down" more than others, but it is more because of absorbtion than scattering.

I can't seem to let go of this Kelvin/PAR thing... If we knew what phosphors a fluorescent used, and what peak frequencies they emitted, could we at least estimate PAR? In theory?

[jmhart]

I can't seem to let go of this Kelvin/PAR thing... If we knew what phosphors a fluorescent used, and what peak frequencies they emitted, could we at least estimate PAR? In theory?


Yes, but in practice putting together than information into a useful "rule" would be an extremely difficult task, because in order to use it, you would have to know those specifics of every bulb you considered. It would almost have to be a spec that manufacturers provided.

Rather than urge them to provide that, I rather ask them to provide PAR values for say, 12" away from the bulb. This would be a useful number for comparing bulbs.

[cellodaisy]

I rather ask them to provide PAR values for say, 12" away from the bulb. This would be a useful number for comparing bulbs.

I'll second that!

[Phyroath]

As a novice, I am waiting for the final result - found this site: Why water is blue http://www.dartmouth.edu/~etrnsfer/water.htm and http://www.americanaquariumproducts.com/Aquarium_Lighting.html
(http://www.americanaquariumproducts.com/Aquarium_Lighting.html)

[plantbrain]

Yes, but in practice putting together than information into a useful "rule" would be an extremely difficult task, because in order to use it, you would have to know those specifics of every bulb you considered. It would almost have to be a spec that manufacturers provided.

Rather than urge them to provide that, I rather ask them to provide PAR values for say, 12" away from the bulb. This would be a useful number for comparing bulbs.

Yea, x2, the other thing, is that new bulbs are made every year and flood the market or new bulb technologies, such LED's, T5's reflector.
Most of the research on light uses PAR, there are trade offs for each method etc, cost, effectiveness, etc.......but the PAR meter is reasonable cost wise for a club to loan out.

No meter is really worth it to have for a single person.
Measure, do your test, then loan or rent it out, you will not likely use it much thereafter.

then you can compare folks's light for their plants at that time and in space. After all, the light changes as you get closer, and as we saw with the ADA lighting, it was much lower PAR than anyone had suspected.
So that type of info in much useful and predictive than watts/m^2 etc.
You would have never caught that using such rules and it does explain a lot when you look at dosing and CO2 demand etc. With less light, you can get away with a lot less. But if the light is not comparable, you add 2-3x as much light and wonder why it does not work/has lots of issues:silly:

All the folks that cried, whined, hooted and hollered over the last what? 20 some odd years about "light rules" and how to fix things never bothered to test it. Playing with silly conversion factors instead. Many of them harassed me about not testing NO3 via EI etc and suggesting people add non limiting nutrients ironically.

I know when and what to test for however.
This is classic case.

Reef folks got it, they spend lots of $ and time testing and measuring and doubting themselves. Not much with the plant folks' crowd.

When testing using a water proof probe like the Apogee, you can measure how light intensity changes through a week at the very tip of a stem.
This is interesting because you soon realize the plant is exposed to exponetially higher and higher light as it grows, then you trim it, and the prcoess starts again.

How does this light intensity change affect the system?
What does this do to CO2 demand?
NO3? PO4? demand?

Think it changes through time and space?

Now you have a tool that can get data and answer such things for light.
How does pruning affect light getting to the plants and how much should/do I do?

Now you can measure those things, measure all points in the aquarium, measure and compoare any bulb.

It would be nice to have a PUR meter that would give the units in terms of bioavailable light and what is used. They have such things but they measure light use indirectly for terrestrial plants.

They can measure bulbs etc with them and all, but they are not pactical or cost effective for us.

There are trade offs with every unit etc, but PAR weighs them all pretty well and is a good standard for aquarist and biologist both.




Regards,
Tom Barr

[cellodaisy]

As a novice, I am waiting for the final result - found this site: Why water is blue http://www.dartmouth.edu/~etrnsfer/water.htm (http://www.dartmouth.edu/%7Eetrnsfer/water.htm) and http://www.americanaquariumproducts.com/Aquarium_Lighting.html
(http://www.americanaquariumproducts.com/Aquarium_Lighting.html)
Ha! I don't think there will ever be a "final result." Too many variables and almost as many opinions as there are aquarium-keepers. Nothing will ever beat experience and testing (as plantbrain pointed out) and we'll never get it perfectly right... but that doesn't stop us from trying! :)

[jpappy789]

Very thought provoking post Tom!

[leeser28]

Great and thought provoking discussion. I decided to see if I could find PAR for my bulbs just out of curiosity and found this site -- it's not about aquatic plants and it's focuses on CFL bulbs, but I thought some of you might find this interesting.
https://growguide.opengrow.com/CFL_Lighting_101

[THE V]

Allow me to muddle the waters a little.

Lighting in aquaria is based upon research in the greenhouse and open field. Very little has been done in aquaria. The information has been extrapolated from the terrestrial sources and much of it may not apply because of the effect of water on light.

There are actually only two main wavelengths of light that are needed for plant growth - 430 & 662nm. This is because there are two different types of chlorophyll molecules. Different species of plants produce the chlorophyll molecules in different ratios.

The photosynthetic radiation needs for different species are not the same. Some are adapted towards using more in the 430nm while others use more 662nm. Just measuring PAR does not effectively correlate to total photosynthetic activity in all species.

If you have some spendy equipment, it is possible to measure the photosynthetic activity of the leaves. This is done by testing for total nitrogen content per gram in the leaf tissue. It has been shown that there is a very strong correlation between nitrogen content and photosynthetic activity (given nitrogen is plentiful). This is the only way I know if to quantatively test the effectiveness of the lighting on the plants.

I just wanted to point this out because biology likes to make and break rules. The correct answer to how much and what type of lighting for a tank is always .. "It depends...."

[cellodaisy]

I just found this interesting comparison of specific bulbs: http://www.aquabotanic.com/lightcompare.htm. If you scroll to about halfway down the page, you can read this person's conclusions. This is what caught my eye:

The most important conclusion in my opinion is that the efficiency of converting electrical energy into PAR light energy is not that different for the several bulbs and technologies included in the sample. The majority of bulbs in the sample deliver approximately (within a 20% range) the same amount of uE/s/Watt in the 400-700 nm range, about 1 uE/s/Watt. High intensity discharge lamps and high-end fluorescents tend to be more efficient, but not by a large factor.

On the other hand, the efficiency of converting electrical energy into visible light energy can be very different among the several types. In other words, the lumen/Watt efficiency can encompass a very wide range, about 200% in this sample. This effect can be quantified by the correlation coefficient between these two quantities, which is 0.56 in this sample. This tells us that no correlation exists between the lumen and PAR output, or, in other words, the lumen efficiency is a very poor criterion for selecting bulbs. We should strive instead for raw power (Watts), since PAR/Watt is on a first approximation the same for most bulbs. The reason for that lack of correlation is of course the broad band response of plants to light, as opposed to the narrow band response of the human eye. Some bulbs are somewhat better than others in converting Watts into photons though, so when efficiency is a major design factor, one should stick with the highest PAReff bulbs. Remember however that in real life, one should be concerned with the overall system effciency, and not just bulb efficiency. This includes the differences between, for instance, magnetic and electronic ballasts. This topic is outside the scope of this article though.
As many have said, there will never be a good "rule" because every situation is different, but as a starting point maybe we need to use watts after all. Round and round we go. :hypnotized:

[thrak76]

Hmmmmm.... that's it?
Great read; disappointing in the end. Not that i expected any kind of real conclusion to be made, but i was greatly enjoying the different perspectives, theories, and analyses.

I've been involved in the stage lighting world in the past, and we used a lot of PAR cans (mostly PAR 64's). Is that reference to the same stats as the PAR in all these posts above? Just curious, as those could be really bright lights, depending on the gel filters used.

[plantbrain]

Allow me to muddle the waters a little.

Lighting in aquaria is based upon research in the greenhouse and open field. Very little has been done in aquaria. The information has been extrapolated from the terrestrial sources and much of it may not apply because of the effect of water on light.


I agree, not much has been done specifically in planted aquariums.
We have done growth studies at various depths and micromols on a few aquatic weeds.

They have entire text on aquatic photosynthesis(I'm looking at a couple right now). It's well studied, but................this is an aquarium, not a terrestrial or natural aquatic system. It's it's own unique system.
Same with each of the 400 or so species commonly kept in aquariums, very few have ever been studied horticulturally and in any real depth, of those, mostly noxious weeds which few aquarist want to keep or are allow too.

However, many folks(myself and quite a few these days) have tested and compared various brands of lighting, asked several questions that make more applied sense to the horticultural question/s. We get the light curves and then compare those to the goals aquarist have.

These are what matters to aquarists.
How does light affect growth through time and space, or on this sized shape of aquarium? What is the best evenness of light spread and what types of light do that? How do I change the intensity easily to control growth rates and algae, and thus=> CO2 demand which influences=> nutrient demand? What light should I buy for my tank?

Some folks want to make a model/calculator to plug a various brand/bulb types and then it would give them a PAR curve for their tank based on the data from a PAR meter, distance plots, in water, ballast type, bulb type, reflector type etc.

Takes measuring a lot of brands etc, but can be done, bit by bit, slowly.
Then new folks can predict the light they need for a given goal.

We know what a micmol range is required for nice slow decent growth for most species already based on nice scapes that have been measured usign a wide range of species(maybe 200 or so thus far)


There are actually only two main wavelengths of light that are needed for plant growth - 430 & 662nm. This is because there are two different types of chlorophyll molecules. Different species of plants produce the chlorophyll molecules in different ratios. The photosynthetic radiation needs for different species are not the same. Some are adapted towards using more in the 430nm while others use more 662nm. Just measuring PAR does not effectively correlate to total photosynthetic activity in all species.


Aquatic plants live in a varied environment, more so than other terrestrial systems typically. This is due to the water and turbidity, tannins etc, depths and water level changes throughout the year/seasons.

They can and do adapt fairly rapidly to changes to the light using Chl a/b ratios, accessory pigments that catch other wave lengths and funnel the energy into the reaction centers for use, most are low light "shade" plants.
Chambers and Lambert's text is good in how plants adapt to various light intensity and quality.

While we can make arguments against using PAR, it is what most use for comparative purposes when growing similar plants and we want to see the effect of light intensity from the same source. Plants adapt and do it well, there's not much difference in aquariums here. Some have suggested using PUR, but again, there's a practical end to this issue, PAR is better than say Watt/gal, and PAR meters are lots cheaper than say a PUR system ........particularluy if it can go underwater.

An oft cited study in this hobby done comparing Cool whites to fancy plant bulbs showed no significance difference. Many aquarist also report the same, however, the aesthetics of cool white are hideous.

"Critical experiments show that maximum growth of most plants under cool white fluorescent lights will be equivalent to or better than that obtained under the blue-red phosphors. Work by V. A. Helson, Canada Department of Agriculture, Ottawa; and J. W. Bartok and R. A. Ashley, University of Connecticut, indicate that there is no advantage to the use of blue-red fluorescent tubes except for aesthetic purposes. Some of the names of these special tubes are Grolux, Plant-Gro, Plant Light, Vita Light and Optima. The higher cost of these fluorescent tubes may be justified on experimental or aesthetic grounds but is hardly warranted on the basis of plant growth."

I read the orignal paper a decade or so ago, basic stuff, but cannot not find the reference since. If there's no difference really between the growth rates(RGR's), then this really does not matter much as long as the PAR is 400-700nm really. Most FL's and MH's fall into that grouping.

Aquarist are not really that interested in every last photon or doing large scale monoculture, they have a wide range of goals. Some only care about color and not anything to do with RGR's.


If you have some spendy equipment, it is possible to measure the photosynthetic activity of the leaves. This is done by testing for total nitrogen content per gram in the leaf tissue. It has been shown that there is a very strong correlation between nitrogen content and photosynthetic activity (given nitrogen is plentiful). This is the only way I know if to quantatively test the effectiveness of the lighting on the plants.


N is not always plentiful(some limit it and forget to dose KNO3 etc and not all plants have the same N demands) and no aquarist I've met will do this for each plant and for each species. A Li COR 6400 will do this as well without destructive sampling but not for submersed plant growth.
RGR's also can do this if you are interested in light per unit of biomass yield.

Aquarist tend to want to know what amount of light do I need to have a certain aesthetic goal.

Ther Apogee PAR meter is a useful meter for this comparative purpose and at 200-300$, and tested side by side to the LiCOR 193 intengrating sensor was only off by less than 5% down to 80cm depth. Not bad.


I just wanted to point this out because biology likes to make and break rules. The correct answer to how much and what type of lighting for a tank is always .. "It depends...."

Horticulture adds an aesthetics factor and is dependent of that person's goal/s.

A good question is what is in the min amoutn of light in Micromols (LCP) and what is the max light where no more growth is produced for a set of aquatic plants??

Here's a good paper that also includes CO2 compensation points as well:
http://www.plantphysiol.org/cgi/reprint/58/6/761

Read that and the conversions for mM of CO2 to ppm is 44
So at 20-30ppm or so(0.5mM to .8mM), we have non limiting CO2 for any light intensity. At least for these 3 very agressive aquatic weeds.

Aquarist typically use 20-30ppm of CO2.

Hydrilla has a LCP of about 12 micromols, not much.
Plants also can take the resources from a higher light region and extend into even more shaded regions in hopes of gaining nutrients and CO2 less than the LCP, Crypts, and anything with rhizomes, tubers, buds, stolons can do this.

Still, a PAR meter is pretty useful and a practical tool to compare light between aquariums, lighting types and brands, space and time changes, for aquarist.

It'd be nice to do all sorts of test, but unless you have the time, and $, some trade offs have to be made.

At 200-300$, a PAR meter shared amongst aquarist clubs works very nicely.
ADA's lights put out much less intensity than I and anyone had thought.
This explained a great deal as far as why they had little issues, when we thought the light was almost 2x as much using the watt/gal rule.

Less light= less CO2 demand= less nutrient demand= easier horticulture, but slower more managed growth rates.

Most aquarist seem to like that goal when they use CO2, but many think more light is better, it's not, it's just more work.

Check out that paper.
If you want more, I can suggest a ton of references.

If you find that one from the Canandians on cool whites, I'd be interested.

Regards,
Tom Barr

[plantbrain]

Very thought provoking post Tom!

So take a look at the paper I cited above also then.
See how CO2 and light are related?

Light is very stable in aquariums in general(more so than anything else for the most part), nutrients would be second but CO2 is really all over the place.

How does CO2 affect light and it's use?

Take a long look at Ole's comments on Tropica's web site.

Click on:
Aquaristic (http://www.tropica.com/article.asp?type=aquaristic)

then click on the Biology of Water plants.

There's a good series of articles on Riccia and the response of light and CO2.

My point is to get folks to focus more on good use of the balance of light with good CO2.

Lower light= less CO2 demand, so it's easier to manage and add CO2 with less risk to fish and for algae. This means less work(less pruning/less dosing issues, more flexibility), and less algae etc.

Too many folks have HLD(High light disease)!

This leads to many new folks having multiple issues that are difficult for them to see and tease apart. add plenty of web misinformation, now you really have a large problem.

They get pissed off, frustrated and leave the hobby.

Cannot blame them.

Plants can survive at even lower levels of light if the system is enriched with CO2 because now they do not need to have lots of Rubsico around to scavenge for any small amount of CO2, they can spend the energy and resources like N trying to get all the light instead.

Low light = less work
As the growth rates are less, so are the algae growth rates(which unlike plants, are never CO2 limited).

This is often counter to the typical advice on line, you do not need CO2 if you have less than say 2w/gal. so most assume that if they want better results, they need more light and add CO2.

Actually, they should just add CO2.
If that rate of growth is not enough, then they can consider adding a pulse of midday light for 2-4 hours, if that's still not enough.........then they can go whole hog adding 3-4w/gal or T5's etc.

That's just more CO2/nutrients, dosing etc, and pruning. It's harder to aquascape with that type of set up over time. If you are motivated, experienced and like to prune, then that's a good thing, but many are not.

Give the article a read, it's been out for a long time, but many have not read it that have gotten into the hobby the last few years.

There are other good articles there.

Regards,
Tom Barr

[Star_Rider]

great info tom


and my tanks seem to confirm this as I have 29's with 65/55 watt 6700-10k bulbs no CO2.

slower growth that is manageable. I may add DIY CO2 to see what happens.
algae in these tanks with the exception of GSA is minimal and manageable .

[plantbrain]

great info tom


and my tanks seem to confirm this as I have 29's with 65/55 watt 6700-10k bulbs no CO2.

slower growth that is manageable. I may add DIY CO2 to see what happens.
algae in these tanks with the exception of GSA is minimal and manageable .

Since the tank is small relatively, and there's a little algae, Excel might be a better solution for you. It's about like 1/3 the rate you'd get with CO2 gas.

I'd add about 15mls every other day.

You'd get more from that light.
How you scape and what plants you chose and where you put them also play a huge role in lighting.

Example:

E. tennellus down front, then a nice rock, followed by some Crypts, then some Java fern, and finally in the rear forming an canopy that hangs over and shades the other plants to the rock ....say Ludwigia acruata

The light will be say 200micromol at the L acruata, below it only say 30-50 micrmols and then the tennellus might have say 60-70micrmomols.

Plants shade eachother and form canopies and move as they grow.
The light changes dramatically as a result.

A single stem of L. pantanal will grow from 40 micrmols at the bottom of my tank, and 3 days later be at 100, then 4 days later, 180, 3 days from, 270 and at the surface.............but..........only for the top of the plant, and there is light hitting it from 3 different angles due to different bulb sources in this tank, as well as reflectance from the glass and other plants, wood etc.

Using a Apogee PAR meter works pretty good at integrating the various reflective valves vs a sphere integrating LiCOR probe, so this is fairly reasonable.

I'm interested in how plants adapt and function at the gross level, the stem, the canopy etc through time as they grow. What their CO2 demands are at different points along the stem and various ways to measure that.

Planted tanks are not static, however, many hobbyist assume that they are. A light meter quickly details that is not true in a quantifiable way.

So it leads to more interesting questions

I do find it rather odd how many have long claimed the need for testing NO3, PO4, etc, yet do not measure light, which is where plant growth starts in the first place. Then they do not calibrate their test kits either. Light can be calibrated by using a new light bulb, measure the itnesity at a known distance, then store than light bulb and test the meter against it every so often, do not use the bulb for anything else..... this works pretty well.

CO2 is much worse as far as measurements.
I've gone to partial pressure and use an optical probe, then am still trying to gerry rig a Neptune AC3 pro to accept a mA signal and use a 50ohm resistor to convert the signal to mV and use the redox port.

This way I can monitor CO2 much better to within 1ppm without any pH/KH carbonate or other buffer interference.

Nutrients, CO2 and light are all related and play large roles with respect to the others. You cannot fairly gauge one without providing some reference(eg non limiting) for the others. Aquarist often make this mistake and have extreme trouble trying to isolate their problem. This is mostly due to too much light and poor CO2/assumptions about either/both.

Ironically, nutrients are farther down the scale in importance, but the test kit crowd still rattles on:o

I'd focus on larger fish like light and CO2.
Lots more stuff to play with and far more complicated than many initially assume, few would argue that point!

Still, you have to cut your losses and make some assumptions, an Apogee PAR meter makes a good choice. We have 2 for each club here. I have one of my own and a LiCOR. But I do aquatic weed management professional, so I have a bit reason and passion to address this stuff.

Still, I started out as hobbyist kid.


Regards,
Tom Barr

[Star_Rider]

thank you , I'll give excel a shot