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04082013, 10:13 AM  #1 
Algae Grower

HOW TO Calculate your tank lighting (in LSI)HOW TO CALCULATE YOUR TANK LIGHTING (in LSI) (LSI, LUX, & WPG included in MS Excel Calculator) I will show you the way to calculate your Lumens per square inch (LSI). This method does NOT account for reflection, refraction, absorption, type of light source, reflectors of fixture, age of lights (intensity loss or spectrum shift), spectrum quality, depth of tank, nor any other factor that will reduce or increase lighting in your tank. This How To is ONLY to give you an idea of how much light you possibly have. The best way to know how much light you have is not by calculating your light but measuring your light with a PAR meter. If you dont need this kind of accuracy, then this How To can be helpful. AND NO there is NO true factor (constant factor) to get from LSI or LUX to PAR (fudge factor is manufacturer, reflector quality, etc dependent). And no this does not guarantee your plants to thrive. **EDIT ** Remember that the reflectors on your fixture GREATLY affect your calculations. There are some grossly generalized factors that I have posted in the manual calculation below. After understanding how to manually calculate your LSI, you can download my edited version of Brokefoot’s excel calculator to automatically calculate your LSI, and even LUX at the substrate or any height; AQUARIUM LIGHTING CALCULATOR 1.1 (LED fftv edit). Or if you wish, skip all the discussion and go straight to the automatic calculator at the end of this post in the attached file. For a more indepth article to read about lighting for both FW and SW tanks click here GLOSSARY (partial lay person version)
Now lets do some calculations My tank is 36”L x 15”W x 20”H. Because the back of my tank has a built in sump, and taking useful internal measurements, that leaves me with 35.5”L x 10”W x 19.5”H to illuminate.The area to illuminate is the LENGTH X WIDTH 35.5in x 10in = 355in^2 (read as 355 inches squared; which is in units of AREA) Now lets look at the light source My lights are four 36” 39 watt T5HO tubes. These types of lights give 88Lumens/watt (it may be less or more, this depends on the manufacturer). This is generic ratio that some agree on. To get total lumens we multiply 4 x 39watts x 88Lumens/watt = 13,728 Lumens **EDIT** These total lumens assumes you have the absolute PERFECT reflectors. If you have crappy reflectors you may have a reduction in lumens by 1/4 to 1/6 (assuming low reflectivity properties to better reflective properties in that order). If you have very good reflectors you may have a drop in lumens by a 400 with a variance of +/ 200 Lumens depending on your reflectors and position of tubes in the reflector. NOW WE CALCULATE LSI LSI is in the units Lumens per square inches, therefore we divide our total lumens by the area we calculated before 13,728 Lumens = 38.7 L /355 in^2 = 38.7 LSI /in^2 (the excel doc has my tank as an example) **EDIT**  PLEASE understand that this calculation gives you total lumens over the area in question, provided that ALL THE LIGHT provided by the fixture is TOTALLY contained within the tank. We all know that this is NEVER true, so you're realistic LSI will be LESS than calculated. Once all the affecting factors (reflection from reflectors, reflection off surfaces, refraction through and out of the tank, etc) are at least recognized, then we can try to take them into account and arrive to an LSI that is less riddled with error. But to make this slightly more approachable I am not including these factors currently (but maybe in the future with more collaboration). To understand what range my light falls under I will be using something similar to REXGUIDE website (found by clicking here) which has the high range for lighting which has far higher ranges than what Tom Barr and some other old timers for planted tanks agree on. The newer generation agrees to the higher range. I personally use the higher range because when using the older timers range I noticed significantly less growth and less color (other than green) of the plants. Here is a version of the newer generations range. Compare your LSI to these ranges or the range on the excel calculator (which is another range that some agree on) Due to keeping this simple, I will NOT talk about the factors that can increase or decrease your LSI, nor how it affects LUX. There is more math involved which scares many. If you wish to discuss these topics, go ahead, but you can find many arguments against LSI and LUX as a way to determine your lighting. To reiterate, this is not the best way to know your lighting, but it is an attempt to give our community a way to calculate our lighting (not measure like PAR). ************************************************** ************************************************** **** AQUARIUM LIGHTING CALCULATOR CLICK ON THE ATTACHMENT TO DOWNLOAD THE EXCEL CALCULATOR Download the attached excel document at the end of this post. In order to view this document directly from your computer you must have a program to open the document type. Another way to view the document is by using Google Drive (previously known as Google Docs). You can upload the attachment to your Google Drive and play with it there if you do not have Microsoft Excel, OpenOffice, or some excel viewing AND editing program (you must be able to edit the excel to use the calculator) TIPS AND ADDITIONAL INFO
The original calculator was provided by Brokefoot on www.aquaticplantcentral.com The link to his page with the original post and original excel calculator can be found by clicking here If anyone wishes to make their own PAR meter you can diy it by following Hoppys post here Q & A Question by Justin on FFTV"What is the best light for plants? What do i need to look for when getting a light? par or wpg?"
The old timer range for PAR is this
the young generation uses a range like this
Plants can adapt to many light ranges, which is why I believe we have such a huge argument about agreeable ranges between old and new tankers. BTW while we can talk about WPG, but I think we shouldn't Because we can have different intensity of light as we go deeper in to the tank, how does that then make sense when putting plants higher in the tank (eg on DW high in the tank) as opposed to the very bottom (eg carpeting plants which get the lowest lighting) This is why using PAR is so great. With a PAR meter we can measure the lighting on the DW high in the tank, or the carpet at the base of the tank. DISCLAIMER Some of the information in the links are old. If you can find new information that people can agree on that modifies this information or links, please let me know. I will include the changes as an edit and mention your name near the edit. I wish for this thread to be a collaboration for those of us who do NOT have access to a par meter. If you do have a par meter but wish to participate in helping this becoming a valued tool, then by all means I welcome your input.
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TankFlip
Last edited by ucrdave; 04092013 at 08:23 PM.. Reason: Some generalized factors put in manual calculation. 
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04092013, 06:03 AM  #2 
Planted Tank Guru

Isn't it self evident that if you put 108 watts of T5HO bulbs over a 55 gallon tank the amount of light you get depends on how good the reflectors are. All of the lumens produced by the bulbs do not reach the tank unless you have good reflectors, so more than half of the lumens are wasted if those are just bare bulbs. Any calculator of this type just has to include a reflector factor to be of any use at all.
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Hoppy

04092013, 06:08 AM  #3 
Planted Tank Enthusiast

Great article. I need to read this several times to master it.
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Patience once drove a man insane
Thanks for your time Danny Tejeda 
04092013, 12:32 PM  #4  
Algae Grower

Quote:
**EDIT** General fudge factors have been put in place for the manual calculation, however they are not included in the auto calculator untill confirmation of my factors seem reasonable. These changes should make your example go boom into the wind (╯°□°)╯︵ ┻━┻ If one understands that with different reflectors one can increase or decrease the intensity of light over a surface, then one could subtract or add more lumens from ones' total to achieve a calculation with more confidence. Unfortunately, many people do not understand which factors affect the final outcome. PAR meters take the guess work and laborious calculation off the table. With PAR meters we can see great work in compilation of measurements such as yours and others on this site. Hoppy (or anyone), can you direct me to a link that gives some basic factors for the most common reflectors for t5HO fixtures that are trusted by many? I would like to include it in the calculator and main body of this thread. I hope that the manual calculation in this post helps to make this calculation approachable...
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TankFlip
Last edited by ucrdave; 04092013 at 08:36 PM.. Reason: inclusion of fudge factors 

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calculator, lighting, lsi, lux, par 
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