# Aquarium Lighting Calculator (1st Draft)



## brokefoot

I have recently started my first planted aquarium (NPT), and built my own stand and hood. In the process I have been doing a ton of online research to figure out how much light I need and which bulbs to use. My DIY hood has screw-in sockets, limiting my options.

After learning of all of the uncertainties of Watts/Gallon estimates as well more than I cared to know about lumens, lux, par, pur and photosynthesis I came up with the attached Excel calculator. It uses Lumens/Watt figures that can be found for most bulbs along with tank dimensions to calculate LUX at a given depth. That can be compared to a table of LUX ranges ranging from "Very Low" to "Very High" light levels (this is the least certain part of it, and the one I'm most interested to get feedback on) I know that Lumens/Lux refer to the visible spectrum of light that doesn't correspond to the photosynthetic range...but I am not going to be purchasing a PAR meter anytime in the near future.

I have read many threads on this subject, and can find no other quick calculation that will put you in the ballpark of lighting requirements. I have also seen that the "standard" bulb people use for the watts per gallon estimates varies greatly. Some say the T-12 is the standard (~60 Lum/Watt), while the oft-referred to Rex Griggs LSI method appears to use T-5 as the standard (~90 Lum/Watt). 

This is meant to very quickly get someone in the ballpark of meeting their lighting requirements. I would be very much interested to hear from experienced people as to how this calculator's results compare to their experience. 

Thanks for any input, and I hope this ultimately helps someone.


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## Michael

Very interesting! In the bulb type--lumens/watt chart, it gives two values for T5: 88 and 98.4. I assume that this is the difference between NO and HO. Is this correct?

I'm glad you included this, because the lumens/watt value was not given anywhere on my recently purchased Coralife 6700K NO tubes. (Yet another reason I dislike Coralife!)

Using the 88 figure, I calculate a Lux @ depth value for my 40 gal. breeder to be 6,398, at the low end of the very low light category. Intuitively, this seems to be an underestimate of my light levels, since I am getting good compact growth from medium light genera such as _Bacopa_, _Nymphaea_, and _Saggitaria_.

This is not meant to discourage you--quite the opposite! With some tweaking and testing, this could be a very valuable tool. As you point out, it won't replace a PAR meter, but it could eliminate some of the guesswork in choosing a light fixture.

--Michael


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## dstrong

I don't mean to sound like a downer but its completly pointless to figure lux and lumens per watt because its only what your eyes see. It has nothing to do with growing plants so if you like what a certain light looks like on your tank then I would say your more than in the ballpark for those figures if you know what I mean.


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## brokefoot

Michael, as I'm sure you know all of those types of lights have a range of outputs. I tried to find the most typical values for those who couldn't find lumens/watt for their particular bulbs. On the T5 I just put that range because I couldn't decide what figure was more "typical". I don't know what would be appropriate for your bulbs, but I would guess 88 as well. 

Would you mind posting your tank dimensions and what you would consider your light levels to be (low, medium?)? This is exactly the feedback I want to try to tweak the calculator. 


dstrong, I realize that PAR & lumens/lux don't correlate really well. But they are related...for a particular bulb, when wattage goes up, lumens goes up, and PAR goes up. The relationships are indirect and vary significantly between bulbs, but most bulbs will grow plants, and the more light that comes out, the more they will grow. 

People have been getting by with watts per gallon for many years. It is extremely problematic, but not entirely useless. I am hoping this lux approach, while still being problematic, will be even more useful for those without a PAR meter who just want to hit a target light range without doing a master's thesis on lighting.

I'm hoping that I can get enough people to post tank dimensions, bulbs and their thoughts on their light levels that we can verify whether or not this thing actually produces usefull results.


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## dstrong

I see what your saying I just wanted everyone to keep in mind that there are bulbs on the market listed with outroarously high LUX that have very crappy PAR so everyone should really try and get a PAR rating or at least a spectral graph before they buy any lighting product. If the entire industry demanded it I think the information would be much more readily available and accurate. I do think this is incredably more useful than W/G though.


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## Michael

Happy to! This is a standard 40 gallon breeder, 18" x 36" x 17" tall. The light fixture is suspended about 4" above the rim of the tank. The fixture is actually 48", and extends about 6" on either side of the tank. It is the old Coralife two tube T5 NO slim profile fixture with their bad mylar reflector. I try to use 6700K tubes with good output in the red and blue wave lengths, but these are becoming very difficult to find. Coralife still sells them, but they are expensive and only last about 5 months! (Ask me why I dislike Coralife.)

Using Hoppy's light intensity chart, this should give me medium light. And my subjective impression is that this is correct.

Mick, what I hope this calculator will do is act as a guide to help new hobbyists and people who do not have access to a PAR meter. People should be cautioned that it is valid only for full-spectrum lighting that has good output in the red and blue wave lengths, as well as the yellow and green part of the spectrum that our eyes are most sensitive to. In a perfect world we would all have PAR meters, but as the ancient Greeks said, sometimes the perfect is the enemy of the good.

P.S. Mick, I was writing this as your last post went up. I think we are all on the same page.


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## brokefoot

Ideally all bulbs would have a full spectral profile and PAR data. It would be great if we could put together a database/table of bulbs with that info in the meantime. 

No doubt that there is a lot more to lighting. My frustration has been with smply figuring out how to get started with some certainty. I was shooting for a minimum lighting threshold that would grow many plants within the Walstad NPT approach. 

It shouldn't be that hard to find that kind of basic information. I've read a dozen threads that just result in a general impression that no one can possibly know anything about lighting without a $150 PAR meter. That is just silly and overly academic.

If you read this post, please contribute your tank dimension, bulb info & lighting level thoughts. 

Thanks a lot!


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## houseofcards

I appreciate your effort, but IMO these light charts and/or calculators simply don't work. There are too many different types of bulbs, manufacturers, setups, plants, goals, lifestyles, etc to calculate in for this too be very useful. 

Even within a certain bulb type. Let's say T5HO. There is a wide variance of light intensity that one light with the same size bulbs would give off. Sometimes the differences have been 2, even 3x par. Also many run an afternoon burst (doubling of their light) to satisfy certain plants. Is it high-light even if I run the burst for only 1 or 2 hours. See where I'm going. The beauty of the forum is you get to see so many different types of setups in the 'real world' and can make a better decision on that type of info IMO than you can from a chart/calculator.


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## Michael

House of Cards, those of us with sophisticated lighting set-ups using complex variable photoperiods are not the intended users of this calculator. And of course any results one gets from the calculator should be tested against actual experience.

Please offer suggestions to make it work better.

--Michael


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## houseofcards

Michael said:


> House of Cards, those of us with sophisticated lighting set-ups using complex variable photoperiods are not the intended users of this calculator. And of course any results one gets from the calculator should be tested against actual experience.
> 
> Please offer suggestions to make it work better.
> 
> --Michael


Michael, that's my honest opinion. I don't thing they work, period. I don't think having an afternoon burst is a sophisticated lighting system. Even if we put that aside, the intensity of lights within each type vary too much by manufacturer making input impossible. Am I not allowed to state an honest response. Again the beauty of the forum is you can view many different setups that might be closer to what you have.


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## Michael

Of course you are allowed to give an honest response, no one said otherwise.

The calculator allows you to enter a value for lumens per watt. This information should be available from the manufacturer (except Coralife). Therefore, there is some correction built in for variance among the same type of lamp from different manufacturers. This is one of the reasons I think this calculator has a chance of being more useful than other ways of estimating light intensity over aquaria.


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## wet

Hey brokefoot. I agree with the points that these models can only scale so far, but your use of Lumens/Sq. Inch (LSI) and stuff is very similar to the stuff Wizard~Of~Ozz and I came up with on AquariumAdvice.com in 2006 (these are still stickies there): 
http://www.aquariumadvice.com/forums/f24/updating-the-wpg-rule-theory-69964.html
http://www.aquariumadvice.com/forums/f24/survey-for-updating-the-wpg-rule-theory-70271.html

Kind of a bummer to see our metric here without credit to Ozz, despite our metric's faults. You may dig this though: Plantbrain's diss of the method, our response, and my correlating that data vs FitchFamily's great work comparing Amano's tanks: http://www.aquariumadvice.com/forums/f24/updating-the-wpg-rule-theory-69964-11.html










(We had the idea of standardizing back to "Equivalent T12 WPG" for various bulb types after regressing data from AquaBotanic's old collection of the data, different manufacturer ratings for lumens, and a survey of the AA community to build our lighting thresholds. This was shortsighted.)

You'll also find the thread has a few plain text versions of our informal survey to determine lighting thresholds.

All that said, much better to devote your effort to automating/building a calculator for Hoppy's stuff in my opinion. He has made strides with PAR and quantifying light, has a growing sample size, has already attempted to tackle emerging technology (LEDs for the aquarium), and probably explains it all better than anyone.

http://www.plantedtank.net/forums/lighting/105774-par-vs-distance-t5-t12-pc.html

I think that metric has much more potential than LUX. There is a reason LUX never caught on.


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## Michael

Great comments, Wet. Hoppy's charts are the only sensible guide to lighting that I have found. Thanks for the other links, I'll do some digging myself.


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## brokefoot

Wet,

Wow...I wish I had found that thread earlier. I have a lot of reading to do. Also, thanks for the link to Hoppy's thread.

I was not able to get the links to work to actually see Ozz's paper or calculator. Is it still available somewhere online? By the way, I would certainly have credited Ozz had I seen his thread. I got the math for the calculator from some other thread on another forum that I can't seem to find again.

I have not read all of that thread on Hoppy's charts, but will try to go through it tomorrow.

Maybe I'll need to change directions on my calculations. I went with Lux as opposed to PAR just because I found a way to estimate it. 

But I still would like to have a calculator that would help someone (including me) quickly figure out how to meet their lighting needs without having to read 50 pages of forum threads. Does such a thing exist that is readily available? Maybe I just haven't found it. Obviously people have spent a lot of time and effort looking into this topic. I don't want to re-invent the wheel.

Thanks again for all the feedback and links!


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## dstrong

Maybe I'm thinking to simply but why don't people request PAR info and spectral graphs from the manufacturer if its not on the packaging? I can't afford a PAR meter and that's how I figure my lighting needs, I just won't buy anything that's supposed to grow plants if the manufacturer can't even supply that information, and if I have that information I don't need to figure anything because I know what I have. I don't mean to downplay the work you guys put in, I think its great, but I'm just spitballin.


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## brokefoot

dstrong, good point. My thinking is just that it would make life easier if that PAR/spectral data were gathered together in one place for many common bulbs.

It would also save some of us lighting newbies lots of trial/error (read money/time) going through multiple bulb configurations.


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## dstrong

True I'll see if I can find the PAR info I used to have for my bulbs


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## houseofcards

brokefoot said:


> dstrong, good point. My thinking is just that it would make life easier if that PAR/spectral data were gathered together in one place for many common bulbs.
> 
> It would also save some of us lighting newbies lots of trial/error (read money/time) going through multiple bulb configurations.


This is why it's tough to categorize these things into nice, neat buckets. The PAR values change dramatically based on reflector design. The same bulbs can seemingly have different PARs, in fact the PAR values can be so different that one might have low light and another medium/high light with the same bulbs but a different reflector. This has been discussed in hoppy's chart. A lot of the data is based on one light manufacturer which was not even reflective (no pun) of the market in general. In addition, additives like co2, water clarity, etc. will also play a role in how well a bulb performs. I'm not trying to be negative, just realistic in what constitutes lighting levels in one's tank.


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## dstrong

Well you obviously can't know how much PAR is reaching the bottom of your tank without a meter but I think it would be awesome to have a growing database of PAR information so I don't have to contact the manufacturer every time I want to try a new bulb that has crappy specs on the packaging. Its a given that the PAR will be different with different reflectors and distances but if you know the bulb its easy for any sensable human being to maximize its usefullness without knowing the specific numbers hitting the substrate.


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## dstrong

Crap I didn't save the emails. =/ I had a bunch of PAR info for CFLs and some T5s that you could buy cheap at Home Depot ect.....


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## brokefoot

I have just finished reading all 34 pages of Hoppy's thread. Great info!

I think I am going to completely redesign the calculator in an attempt to estimate PAR using the info in Hoppy's thread. One thing about Hoppy's approach is that it is somewhat limited to fairly standard set-ups. I have a DIY hood with 2 screw-in sockets...so it does nothing for me. It also doesn't have LED's, MH or spiral CF's for example. And, of course, it makes some assumptions that certain bulbs will have certain reflectors.

I would like to try to use the PAR data and fill in the gaps (other bulb types) with the lumens/lux data (converting to PAR as well as possible). Ozz's thread and the accompanying poll are a great data source. I also want to include some options for selecting different reflector properties and a list of different bulb types/brands to give users as much specificity as possible.

It will take a while, but I think it will be a great resource! I welcome suggestions!

I am sure there will be continued posts asserting that the whole exercise is useless. But the dozens of posts I just read on Hoppy's thread confirming that his charts have helped people solve their lighting problems, and their gratuitous thanks to him, suggest otherwise. Many hobbiest are like me and don't have a PAR meter, a club to borrow one from, or $200. Plus, like Hoppy said, you have to pick some lights to buy before you can test them and begin your trial and error process.

Thanks for all of the input!


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## Michael

Brokefoot, DFW APC is in the process of buying a PAR meter. We hope to accumulate data on many different types of set-ups. Let me know what kind of information is useful to you, and we'll try to collect it.

Truly, I do not think this is a useless effort. As you point out, Hoppy's charts, imperfect as they may be, have been very helpful to many people. I used them to guide my selection of lighting, and they worked for me.

There is also a thread on spiral compact fluorescent lights at http://www.plantedtank.net/forums/lighting/85667-par-data-spiral-power-saver-bulbs-2.html That link takes you directly to the second page, where most of the information is. A very useful thing I learned there is that SCFs are more efficient when mounted vertically instead of horizontally, assuming similar reflectors.

--Michael


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## wet

hey brokefoot.



> I was not able to get the links to work to actually see Ozz's paper or calculator. Is it still available somewhere online?


Yeah, unfortunately the site went offline a few years ago. Last I heard Ozz had moved onto Salt Water but since the challenges are similar, maybe he's brought another site online (I don't know).

I have some stuff though, but nothing that isn't in those threads (I was czcz). Here's the old Excel calc: http://petalphile.com/stuff/lumens_sqin.txt -- sheet 1 just takes your different watt bulb combinations -- T8, T12, MH, whatever -- and then figures out total lumens, lumens/sq in, and the equivalent WPG. Sheet 2 is where the data you'll find interesting is: a average of lumens/watt for various bulbs, then a normalization of that back to "Equivalent T12 Watts Per Gallon" so we're all speaking the same language regardless of bulb technology or tank size.

Here's the survey data. The lighting level column is based on the user's experience. http://petalphile.com/stuff/aa_lighting_survey.txt Unfortunately, I stopped collecting that file once Ozz's old databases were online, and so we lose many datapoints.



> But I still would like to have a calculator that would help someone (including me) quickly figure out how to meet their lighting needs without having to read 50 pages of forum threads. Does such a thing exist that is readily available? Maybe I just haven't found it. Obviously people have spent a lot of time and effort looking into this topic. I don't want to re-invent the wheel.


I agree with these goals and, yes, as flawed as using Lumens (LUX, etc) is, they get us into the ballpark.

Put another way: if some tool and user experience gives us confidence in how some metric scales -- say, it works on 80% of tanks, but for 20% the metric doesn't capture whatever variables would better predict tank behavior/requiremnets -- that tool is valuable! But will it change the hobby? Will it actually get widespread adoption? That remaining 20% is important.

This is why its smarter to start with PAR. Build the models around that metric and not only are they more predictive, I suspect you'll find the traffic comes easily. And I'll bet you'll find help from collaborators if you want it. (I'm volunteering.)

dstrong,



> Maybe I'm thinking to simply but why don't people request PAR info and spectral graphs from the manufacturer if its not on the packaging?


Yes!

houseofcards,

These are great points of course. There's some fudge factor that can be built into the buckets, though. I'm of the opinion the calculator shouldn't account for such things as reflector quality or water clarity: these are things that are the responsibility of the user. The calculator is just a (ideally free) tool for those who haven't bought the (expensive) proper tool: a PAR meter.

I get why that's wrong to lots of people though. I just think focussing on the edge cases stops development of tools. (And once the tool is alive, we can go back to focussing on edge cases, or pondering them like we do today without tools.)

In terms of not enough samples for the bulbs: Yes! When we collected data, we dropped outliers to try to reduce noise, but it was quick and dirty. This is just a problem solved with clubs like Michael's or Hoppy's spreaing around PAR meters though, and volunteers searching Google.

Just my two pennies, of course!


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## brokefoot

Wet - Thanks for the data & links! 

Michael - I think that the more PAR measurements with setup details we have the better. At this point I'm thinking the most relevant details are:

* Tank dimensions
* PAR @ substrate (and depth if dif from tank height)
* Lux @ substrate (if your meter reads both; it might help build a lux/par relationship database for * particular bubs)
* Bulb details (including any manufacturer specified lumens or PAR values)
* Reflector type

With regard to Wet's thoughts on leaving reflector and water quality variables to the user...I agree about water quality. It seems easiest to just assume clean water instead of having people guess at how stained their water is. On reflectors, though, I'm not sure. I don't know just how many types are out there and how difficult it would be to have people select their's accurately. I was thinking just a pull-down menu where they select "Good", "Average", "Poor" or "None" for reflector. Their could be some information their to help people determine their reflector quality. I welcome thoughts on this and any other potential features.

By the way...PAR will definitely be the metric. I am just thinking that all of that lumens data represents good depth/light attenuation information that could be used. If there is enough lux and PAR infor for SPECIFIC bulbs I think a lux/PAR conversion is possible. You just can't generalize it.


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## wet

Rad.

One of the most interesting and practical things I'd like to know is how the tank's gardener finds their tank acts. High, moderate, low, etc light. I hope you also collect this so we can compare that to PAR.


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## houseofcards

Thanks Wet, I appreciate your comments. To be honest I was following hoppy's thread for a while, but there's just too much variance within the same bulb type for me to really put serious credence in it. I saw triple PAR readings for the same T5HO based on different fixture manufacturers. Yes there are people that buy lights based on it, there are also those that underestimate their lighting needs and can't get things to grow since they went by the PAR reading in the chart that wasn't representative of the most fixtures on the market. Don't get me wrong it's a good effort, but I just don't think it 'really' works. In theory it might, but in the 'real world' with the variables I mentioned I don't think so. Newbies are the ones that wouldn't really be thinking about co2 effect, water clarity, plant shading etc. and would simply buy the light based on a PAR reading from one manuf. 

According to the chart 150watt mh light on a 60cm tank hung around 30cm would be 'super bad ass high light'. No one would buy it based on the chart data, but according to ADA that is the standard light for a 60cm (2ft tank). So how do they produce such stunning results from what according to the chart would be an algae-ridden mess? Doesn't ADA know what they're doing? It's more about discipline and learning from the forum then about looking up a number in a box. These tanks don't exist in a laboratory and one's lifestyle, commitment, etc. will prove more worthy then trying to hit a bulls eye with a light recommendation IMHO.


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## brokefoot

wet said:


> Rad.
> 
> One of the most interesting and practical things I'd like to know is how the tank's gardener finds their tank acts. High, moderate, low, etc light. I hope you also collect this so we can compare that to PAR.


I had planned on pretty much accepting Hoppy's/Tom Barr's PAR/Light Level equivalents...but you are right. It would be nice to have people's subjective/experience-based perceptions of their light levels alongside their PAR readings.

Let's add that to the list.


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## wet

houseofcards: yes, yes, yes! So -- because its relevant -- how do you shop for lights?

(for reciprocity: I l-o-v-e metal halide and/or sunlight. I might love LED -- i don't know -- but the cost of entry is too high for me. I believe once you cross the threshold of "you need to be dedicated for this to work" -- high light -- I don't think levels matter much in terms of CO2/nutrients/trimming. The reason I am interested in light calculators is it's the most $$$ thing for us, and therefore the thing most likely to block new hobbyists.)

brokefoot,

The link above is broken and I can't edit, but the excel spreadsheet mentioned above is at http://petalphile.com/stuff/lumens_sqin.xls

I'll redirect that txt link later. Sorry.


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## dstrong

Houseofcards: I agree with what you are saying and that's why tuning the chart with more and more data will just make it that much more accurate. 150w mh on a 2ft tank might be super badass high light on the chart but it is much more relative than using watts/gallon. A standard 60cm tank I believe is roughly 14 gallons so if someone was going by w/g that's almost 11 w/g. The chart is not intended for anyone with as much knowledge and skill as ADA or anyone of simular caliber. Its is intended for the new hobbyist(as wet mentioned) and the relativly inexperienced who do not have an advanced base of experience and technical knowledge of lights or people looking for a quick reference to get them in the ballpark. So instead of people asking questions about if they have enough light in their tank or what light to buy and getting all kinds of unknowledgable bs and misinformation about their "watts per gallon" they can use the chart as a reference to get a general idea. I think this is a great idea, maybe if enough people start using it as a rough guideline we can eliminate all this w/g bs that floats around the web like some sort of mutated duckweed.


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## niko

Don't know if this is in line with this discussion. To me the watts per gallon number is pretty useless because with bulbs that have individual reflectors and have a good spectrum you can get away with much less light. Like 54 watts instead of 192 for example.

Whatever that means there is a very easy way to compare light intensity (if that is what we are after and not what the plants care for). I assume that each person in the US has a digital camera. It can be used as a very reliable light meter. 

Every modern digital camera, even the cheap ones have manual mode. You can point the camera at the aquarium and take a reading of the shutter speed and aperture. Without going into details the shutter speed/apperture are connected and we can come up with a single number that denotes a low, moderate, or a high light tank. Say to divide the shutter speed to the aperture:

Example:

Shutter speed - 1/15
Aperture - 3.5
----------------------------
LOW light = 4 
(15/3.5= 4.3)

Shutter speed - 1/60
Aperture - 3.5
----------------------------
MEDIUM light = 17 
(60/3.5= 17.1)



Shutter speed - 1/125
Aperture - 3.5
----------------------------
HIGH light = 35 
(125/3.5= 35.7)



--Nikolay


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## Zapins

Hmm interesting niko... I wonder how different each brand is though, and for that matter each individual digital camera within 1 production model.


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## brokefoot

Niko, my goal is to estimate light needs based on tank dimensions and desired light levels. I am curious about how well your approach works, though, for checking existing light levels. Do you hold the camera right up against the glass?


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## houseofcards

Zapins said:


> Hmm interesting niko... I wonder how different each brand is though, and for that matter each individual digital camera within 1 production model.


That and you would also need the same ISO. As you point out I think different brands and different sensitivity it would be tough to get a standard.


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## Zapins

Its a pretty good idea though. I really want someone to try this out and see what the answer is. 

The reading will also depend on how far away from the light the camera lens is.


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## houseofcards

Yes, it is a good idea if there can be consistency. More plausible for people to do that then to think they'll find a PAR meter under the tree this year.


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## Newt

Niko, the camera's light meter probably reads in lumens or lux (lumers per sq. meter). Lumens is weighted towards the green area of the visible light spectrum which is the light humans percieve as brightness. Most plants utilize red and blue light most effieciently for photosynthesis (PUR). I still think the power (microeinstiens) 'behind' the color is what's important.

http://higherintellect.info/texts/d...ery_grow/pubpages.unh.edu/~jwc/einsteins.html


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## dstrong

@newt


niko said:


> there is a very easy way to compare light intensity (if that is what we are after and not what the plants care for).


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## Zapins

I think this PAR business is the ideal situation, but I think basing our lighting needs on intensity rather then the kelvin output intensity is good enough for most practical purposes. Since most of us don't use LED lighting getting a bulb with 1 wavelength output is pretty much ruled out. Perhaps a given bulb is more heavily weighted to the less usable colors, but plants have accessory pigments that specifically collect light waves that are not in the ideal red/blue wavelengths. If the light is intense enough then the plant simply grows more accessory pigments to compensate. So effectively an intense light will grow plants with no special attention to the kelvin rating.

I think in lieu of PAR meters becoming cheap overnight you should design your calculator around intensity. Perhaps in the future the calculator can be added to if people can figure out how to incorporate PAR values in a meaningful way.


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## brokefoot

Zapins,

I have found a great piece of research that I think will be tremendously helpful. This guy Ivo Busko has used bulb efficiency, combined with spectral info to calculate PAR efficiency for many bulbs. I have to get my head around exactly how to use this to estimate PAR at a given depth on a particular setup, but I am confident that it is doable. And I can use actual PAR measurement data to "ground truth" the calculations.

http://www.discusnews.com/article/cat-04/lightcompare.shtml


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## brokefoot

I know it's been a while, but here is my second attempt at the calculator. I still want to do a lot of cleaning up to make it more user friendly, but it is doing the math now.

I really need some feedback testing the outputs against real world PAR readings. Any feedback or questions are welcome.

This whole calculator is based on a compilation of data and information posted on various forums, much of which is thin and/or incomplete. I am sure revisions will need to be made, but I think the approach is sound. The calculator seems to reproduce the data in Hoppy's graphs pretty well.

Again, please try it out and let me know what you think.

Thanks!


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## Michael

Brokefoot, our club just purchased a PAR meter, and we are starting a loan program for members. Anyone who uses the PAR meter is asked to post his/her results in this thread: http://www.aquaticplantcentral.com/...tic-plant-club/80982-par-data-collection.html

If I used the calculator correctly for the 10 gallon in my post, PAR should be around 90, and I measured 60 at the substrate. The fixture is about 4" above the top of the tank, so if it was directly on top, PAR might be 90.

I hope there will be a lot more data in that thread for you soon.


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## brokefoot

Michael,

That is awesome! Thank you. 

One thing I need to clarify on the next version, and that I would ask you clarify to your members... the depth should really be the distance from the lights to the substrate. 

The critical components are:

1) Area of the tank bottom (derived from length X width)
2) The distance from the bulbs to the substrate (depth)
3) Total watts (# bulbs X watts/bulb)
4) PAR Efficiency (chosen from chart to correspond with bulb type)
5) Reflector Coefficient (chosen from chart)

So filling in all of the dark yellow fields in that way should yield the intended result. In the next version I will add a field for height of bulb above tank rim and depth of substrate to calculate the distance from bulb to substrate. I'll also try to make it more intuitive and clear as to how to use it.

Any comments/suggestions/questions regarding making it most useful are welcome.

If I could make one request... reflectors make a massive difference in PAR from everything I've read and the calculator reflects that. I would like to compile as much info as possible as to what types of reflectors are being used (shape, width in relation to bulb, surface treatment). References to hoods or pics online would be great. Would you mind adding that to the list of data people post from your club? Ideally I could have a sheet in the spreadsheet showing various common reflector setups and approximating reflector coefficients specific to those setups.

Thanks again for your help!


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## Michael

Our report form asks for distance from lamp to substrate, so that is covered. I meant to request information about reflectors, but forgot. I will add that.

You are right about the reflector making a huge difference. I suspect that the flimsy mylar reflector is the reason I get such poor performance from my Coralife fixtures.


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