# One Way to Design a Planted Tank LED Light



## Hoppy

Here is one way to design a LED light that will meet your planted tank requirements. Obviously, you first start with the tank you want the light to work with. Next, decide if you want the light to be suspended above the top of the tank, or sit on top of the tank. Suspending it is by far the best idea. Decide if you want to spend a little more money and be able to adjust the apparent color temperature of the light, which requires more LEDs and two LED controllers. 

A very good PAR to design for is 60 micromols per square meter per second. This is medium intensity light - if you miss the target, you should still have either low-medium light or high medium light, both of which are very usable.

Pick the LEDs you want to use: Cree XP-G, which are high output, high power, and a bit cheaper than Cree XM-L, which are higher power, and higher output.

If you will suspend the light above the tank, you will want to use optics on the LEDs to focus the light to reduce the spillover light, and make better use of the full output of the LEDs. For lights which will be less than 2 feet from the substrate, 60 degree optics work well. For lights up to at least 36 inches from the substrate 40 degree optics work well. Decide which you will use.

It is best to run LEDs at less than maximum power to ensure that they will last for many years before “wearing out”. Also, the more power you run them at, the more likely you will need active cooling and a quality heatsink, which add to the cost, the complexity, and the noise. Pick a LED driver or drivers which can deliver the current you want to use.

Look up the lumen output the LEDs produce at that current from the pdf data sheets for the particular model LED you will use.

Write down these parameters:
LED model _______________
LED current_______________
lumen output per LED_______ (L)
Height of light from substrate________inches (H)
Optic cone angle__________(probably 60 or 40 degrees) (ø)

Now make this calculation:









where “a” equals the spacing between LEDs in inches, and “n” equals the number of rows of LEDs to be used.

Assume one row of LEDs will be used, and calculate the spacing between LEDs ( the square root of the result above)

Alternatively, assume 2 rows of LEDs will be used, and again calculate the spacing between the LEDs.

Assume 3 rows of LEDs will be used, and again calculate the spacing between the LEDs

To decide how many rows of LEDs will be best, calculate the spread of the high intensity portion of the cone of light. That will be equal to 2 x H x tan ø/4. That spread should be about 2/3 to 3/4 of the front to back depth of the tank. If it is less than that, 2 or 3 rows of LEDs should be used, to expand the spread.

Now that you know the spacing of the LEDs, and the number of rows of LEDs, calculate the number of LEDs per row. The row of LEDs can end at about one half of the tank front to back depth from each end of the tank, to avoid spilling a lot of light at the ends of the tank. The length of each row will be the tank length minus the tank front to back depth. Divide that number by the spacing of the LEDs (a) to get the number of LEDs per row.

Look at the specifications for the LED drivers you want to use to see the minimum and maximum number of LEDs they will power. Based on that you can determine how many LED drivers you need. If you want to be able to adjust the apparent color temperature of the light you will have to use two colors of white, cool white and neutral white, for example, with separate dimmable drivers for each color. Make sure the number of LEDs of each color is not fewer than the minimum for the driver.

Electrically connect each color of LEDs all in series, up to the maximum the LED driver will power, and connect those to one dimmable driver. Do the same for the other color.

Pick a heatsink or heatsinks that will accommodate the rows and LEDs per row that you will use. If you are using an LED current near the maximum power for the LED model you are using, also figure out a cooling fan or fans configuration to keep the heatsinks cool.

Finally, determine how you will hang or otherwise support the light, and find the parts needed to do that.

Use of a “splash guard” is optional. Lights hanging above the tank do not need any splash guard. Lights sitting on top of the tank, with no glass lid on the tank, may need a splash guard, and will need one if you use an air stone in the tank.


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## [email protected]

I propose this single post be a sticky. Unless there are specific additions that will clarify something specific let us not clutter this one up. Please.


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## KrazyFish

Great info! Thanks Hoppy!


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## BlueJack

Always enjoy reading your posts! roud:


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## wastedtime

Great info Hoppy. Thanks , Nice and concise.


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## Doc7

fizzout said:


> Here is an excel spreadsheet that embodies Hoppy's formula to calculate the PAR (top portion) and the spacing between the LEDs (lower portion). I included Hoppy's suggestion to round off the PAR value. The spreadsheet is protected except for the input cells to prevent loss of the formulas, but you can unprotect it if you are so inclined (there is no password).
> 
> View attachment 44811



I notice that your spreadsheet also requests to use "half the optic cone" angle. Which is a reference to other posts where Hoppy and other have said that this is the area of most intensity.

You do use the same equations Hoppy used above though. IE, you're still dividing the cone angle by 4.

Is this how the equation in the original post of this thread is meant to be used? It makes sense to use the "effective angle" for PAR (half the optic angle, so 20 for a 40, and 40 for a 60), but making sure that Hoppy did not already account for this in his equation?


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## fizzout

Doc7 said:


> Is this how the equation in the original post of this thread is meant to be used? It makes sense to use the "effective angle" for PAR (half the optic angle, so 20 for a 40, and 40 for a 60), but making sure that Hoppy did not already account for this in his equation?


I used the exact formula in the original post by Hoppy, which I assume indicates the use of the "half" angle of a lens. I may have misinterpreted the formula, but from the examples that I saw, I thought the angle was suppose to be half of the optics.


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## Hoppy

The angle is the advertised cone angle of the optic, not half of it. I corrected this on the spreadsheet, and added a calculation for the LED current for Cree XM-L and Cree XP-G LEDs. But, I don't know how to attach an Excel spreadsheet to this post. Once I know how to do that we can include both the correction and the added calculation.

I used the Cree pdf for each LED model and derived an equation that works for most of the range of the Lumens vs current graphs here. The equations work for the 350 to 1500 mAmp range for both of them. For the XP-G the equation breaks down for lower currents, and for the XM-L it breaks down for higher currents, overestimating the lumens produced, in both cases. But, I wouldn't even consider using a higher current for either LED, just because of the cooling that would then be required for the heatsinks.

Thanks to fizzout I learned how to to this: Here is the updated calculator, for which fizzout gets 95% of the credit.

*Edit: Added Cree XP-E-Q5 LEDs which are available at DealExtreme, and which are more suitable for lower height tanks.*
View attachment 44862


*Edit:* Added Cree XR-E-P4 Bin WD (5700-6350K), which are less than $3 each on DealExtreme.
View attachment 44874


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## fizzout

Hoppy, 
Thanks for making the correction. Now the calculator can really be a useful tool for anyone designing a new LED lighting. :icon_lol:


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## Doc7

And with that the light design philosophy for the next 1X years has been written.

Think I'm pretty well set that I want to do an LED next then. Will pick up some valuable soldering/electronics skills along the way.

I know I read Hoppy in another post that the "number of rows" multiplication may not hold up once the spacing between rows grows to the 6" distance which would happen if I spaced out even 3 over the middle 12 of an 18" front-to-back, so I will have to use this thread, other graphs Hoppy's posted, and probably a little guesstimating to figure out how to build a 40B light. I will need to crunch some numbers in Excel if I get a chance this week but thinking I'll try to do it with three rows, but treating the PAR value as "two" rows because of the wide spacing between the outermost front and back. I am presuming, before having done the numbers, if I aim for 50-60 PAR with 600-700 mA this three row design would get me close enough that I could either go down intensity or up, if I'm wrong, and not hit the "min current" or "need cooling" thresholds.

Use of LEDs will allow me to build a light to fit my desired canopy design, instead of building my canopy around desired lights (for T5HO I'd need to be concerned with heat as well as height, on a 40B I will want a "squatter" canopy)



Sent from my BlackBerry 9650 using Tapatalk


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## they call me bruce

Excelent work I just checked my proposed design for my 72x24x24 and its works--I mean its very close to whats been projected before this spread sheet.
Wonderfull job alls left to do is place the order and put it together then comes the par meter--I have full confidence---


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## they call me bruce

Hey doc when will NJAGC update the site --is this group really up and running-
dont mean to high jack thread you can PM me


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## Doc7

The attachments included in the "Edits" above aren't working for me. I may be doing something incorrectly. When I click them, ie. "on DealExtreme. Attachment 44874"

I get: Invalid Attachment specified. If you followed a valid link, please notify the administrator


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## Hoppy

The last attachment doesn't work for me either. So, let's try again:

View attachment PAR_Calculator 5.zip


Now, it works. Attachments are not nearly as easy as photos are.


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## Doc7

Hoppy,

I did some work using the equations and posts you’ve made in this thread and elsewhere along with the excellent spreadsheet tool. I think my questions below belong in this thread because they address a topic that will be common among anyone with wider tanks.

I am working on designing a fixture for a 40 breeder which is 18” front to back. As far as I can find online I haven’t found anyone making one yet so breaking some new ground, in a way.

I don't mean the below to ask, "design me a fixture." Instead I am asking for some clarifications or suggested assumptions in using the equations and sheets to account for cases of widely spread LED rows of 4-5" spacing between rows (and >8" spacing between first and third rows)

As previously suggested by yourself and common sense, I went into this with some “knowns” and requirements for the fixture, to fix some of the variables. I know that I want the recommended middle PAR range of 40-60 as you have frequently referenced, I want even lighting over my tank, no more than 2 LED drivers, dimmable for fine-tuning PAR, passive cooling via aluminum channel or other heat sink, and I wanted to build a canopy that is less than 15" above the tank rim - the canopy height bit is one of the more important variables that can be fixed because it most directly impacts how the LED will be designed of course.

For use in the spreadsheet I chose 20” above substrate as the height. Pending actual builds etc I could vary this up and down within reason, as the canopy itself won’t be built prior to the lights.

I know that an 18” wide 40 breeder with lights 20” above the substrate will require multiple rows of LED lights if I use aluminum channel passive cooling. With 40 degree optics (more on this in a second), at a height of 20”, the “high intensity” inner-half cone diameter will have a 3.5” radius at the substrate surface. To avoid high intensity glass strike, I figured that the starting point for my rows would be to have one directly centered in the tank, one 5 inches from the front glass and one 5 inches from the back glass.

I read with great interest a post you made elsewhere regarding that rows of LEDs greater than a few inches apart don’t add up when kept at a low height, and thus it probably isn’t accurate to use “n = 3” for number of LED rows in this design. 

So, knowing that my front and back rows would be 8” apart, and the center row is 4” from the row on either side of it, it seemed I was at the point where it’s just a guess to select any number above 1 as the “number of rows” combining for PAR.

Using 1.25 as “n” rows to account for the large spread from front row to back row but still account for “some” combination, I came up with the following:

27 Cree XPGs
3.333” Spacing per row, 4-5 inches between center row, front row and back row
20" above substrate
60 PAR
40 Degree optics

Would let me run the XPG at .6-.7 Amps – within the passive cooling range and if I adjust the PAR down it gets better from there.

This seems like a high number of XPGs, and with quite focused Optics, compared to what I’ve seen elsewhere used for tank lighting applications. Do you think I have made drastically wrong assumptions at some point in the process? 

If I change to 60 degree optics the calculated LED current required to hit 60PAR with the 27 XPG (3 rows of 9 at 3.33”) goes to 1.1 A. Way too high for passive cooling. But why would I need 40 degree optics only 20 inches above the substrate?


edit: Of course if I change my assumption to "n=2" which is still of course only 66% of my actual number of rows to account for the spread from front to back, it decreases the number of LEDs required (4" spacing) and amperage as well. Seems like I might need to just experiment. Which isn't so bad anyway - the two worst cases are that I either end up having to go higher above my tank than I wanted to do and possibly rethinking using a canopy, and/or having an extra row of LEDs on a heat sink I can use for another tank. I can't find it but I am sure you have posted somewhere the graph of Cree XPG output vs distance from light (horizontal) at one or various mA? If you have, I would be able to look at that and figure out how much each spot on substrate should get with this setup.


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## Hoppy

Doc7, you ask a number of good questions:biggrin: The equation that this method is based on was derived from data that I have from LED lights with rows of LEDs spaced about the same distance as the LED spacing. But, the maximum LED spacing I used was 3.25 inches max., and the number of rows was 3 maximum. Extrapolating from that will work, but probably not for 3X extrapolations. The higher above the substrate the light is, the more you can extrapolate, just because the cones of light get bigger as you go higher. (I think it is about the overlap of the light cones, more than anything else.)

I suspect that with 3 rows of LEDs, 20 inches from the substrate, and 60 degree optics, and 4-5 inch row spacing, you can use n=3. At 20 inches the center half of the cones of light is about 10 inches in diameter, so there is a lot of overlap of the rows of light. I'm not sure that with 40 degree optics you can use n=3, and I suspect you can't. But, for a 20 inch height I wouldn't use 40 degree optics anyway. A 40B tank is about 17 inches high, so, with 3 inches of substrate, the top of the tank is about 14 inches from the substrate, and a light 20 inches away is about 6 inches from the top of the tank. A 40 degree optic would give a circle of light about 4 inches in diameter at the water surface. These circles of light are very visible when they are that small, and wouldn't look good at all.

The PAR numbers you get with those spreadsheet calculation is for right under the middle of the light, so the distance between the outer rows isn't relevant. As with any aquarium light the PAR will drop off near the glass anyway - theoretically. But, light reflected off of the glass adds to the PAR near the glass, greatly reducing the drop off.


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## j_r_smith

*All white or a mix?*

This is some fantastic information. I have been trying to determine the correct number and type becuase I want to move away from t-5's. As I am reading this it seems to implicate a fixture made up of all white LED's. I have had many recommend a mix of cool white and blu or royal blue. Some at a 1 to 1 ratio and others at a 2 to 1 ratio. What are your thoughts on this? And does the calculation still work for the white only when doing a mix?

Thanks!
Joe

38Gal 30x12x19 planted tank
56Gallon 30x18x24 soon to be planted
95 gallon 36x24x25 soon to be planted discus.


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## cheesehead

*Question on optics angles*

Hoppy, thanks a lot for the work. I've been planning a LED build for my 200 gallon, full spectrum, and have pieced together a spreadsheet with spectral output of various LED's and what I'd need to have to get xxx illumination. I get numbers fairly close to yours for numbers of LED's.

I've got a question on the spreadsheet (ver 5), related to the half angle/full angle question stated earlier. The documentation says that if you don't use a lens for the LED's, that 



> Cone angles for bare LEDs, with no optics installed, XP-G, XM-L, XP-E use 70 degrees, XR-E use 50 degrees


When I look at the spec sheets those look like half of the full width half maximum (FWHM) for the bare LED's (for example, for the Cree XPG the spec sheet the spatial distribution is 50% of maximum at +/- 60 degrees, therefore 120 degree half maximum or FWHM). 

So should the angles for the bare emitters be 140 (or 120) and 100? Or am I miscalculating what a "60 degree optic" is by assuming it's +/- 30 degrees at FWHM?

Thanks.


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## dafil

Hoppy,I am asking for your help and opinion-what PAR will get with these 14pcs 3x1w,60deg optics,28inch from substrate,270lm each bulb


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## Hoppy

How far apart, center to center, are the bulbs? I don't think my empirical equation will be very accurate for this type of setup, but it may be close enough to know if you have very high light or low light.


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## dafil

4 inch betwen the rows.3,5 inch center to center in the row.
10x


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## Hoppy

The calculator says about 30 micromols of PAR at 28 inches.


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## skanderson

im having trouble inputting figures into the spreadsheat. anyone have advice? im planning a led fixture for my new 300 cube build. 48x48x30. thinking of keeping the leds 48 over the substrate and using 30 degree lenses.


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## makutaku

skanderson said:


> im having trouble inputting figures into the spreadsheat. anyone have advice? im planning a led fixture for my new 300 cube build. 48x48x30. thinking of keeping the leds 48 over the substrate and using 30 degree lenses.


The calculator relates six variables. You provide five of them and it calculates the sixth.

You need to answer the following question: what do you want it to calculate ? 

Then you need to provide data for all the other five variables. From your statement you already have:
LED height = 48
Cone angle = 30

If you can get the value of three more variables, the calculator will give you the value of the sixth.


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## skanderson

that isnt my problem, i have 5 of the variables but i cant get any variables entered into the calculator. any advice on how to put it into the spreadsheet or do i just need to do it by on paper.


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## Hoppy

Are you using The Excel spreadsheet program? If so, you should be able to enter values the way you would with any other spreadsheet.


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## m00se

Sounds like it's opening the spreadsheet in read only mode.


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## skanderson

that may be the problem. any way to change that? im not a tech person by any stretch of the imagination.


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## skanderson

i think it is because i dont have microsoft office installed does that sound right?


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## Hoppy

With a PC I think you do need to have Excel or Office installed to make the spreadsheet work. Without it, it is just a table in a document.


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## m00se

I just tested it in Google Docs and it works. Make a new spreadsheet in GD and then go to File/Import and choose "New Spreadsheet" and point it to the xls file. It will upload it then you'll be good.

HTH


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## Wasserpest

Is there a direct relationship between Lumen and PAR? I am not an expert, but I thought they are two different units, and things like spectrum play a role? Like having two LEDs with the same luminous flow, one with peaks in the yellow/green area, another one more in the red/blue photosynthetically speaking more significant area ?


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## mistergreen

Wasserpest said:


> Is there a direct relationship between Lumen and PAR? I am not an expert, but I thought they are two different units, and things like spectrum play a role? Like having two LEDs with the same luminous flow, one with peaks in the yellow/green area, another one more in the red/blue photosynthetically speaking more significant area ?


Yes on all the questions. On Apogee's site there is a lumens to par conversion equation. There is a relationship but it's an approximation for white sun light. A par sensor will have a peak toward the blue.


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## corlis

Comparison of LUX and PAR output for single colour LEDnm. Cyan, green, yellow LEDs have high LUX but low PAR while blues and reds have low LUX and high PAR. PAR graph shows the problem called the green valley issue in LED manufacturing


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## jeffkrol

Hoppy said:


> With a PC I think you do need to have Excel or Office installed to make the spreadsheet work. Without it, it is just a table in a document.


FYI for those not tethered to MS "Openoffice" Calc opens it just fine.. and that is free..


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## ybendek

Hello World 

I'm newbie with LED fixtures and I want to change my current fixtures (T5) to LEDs, I have a planted tank with some carpet plants like Glossostigma elatinoides, Lilaeopsis brasiliensis and Hydrocotyle Tripartita, thus I understand that I will need a good PAR level. I found this awesome tool and I'm trying to use it and estimate a good configuration for my DIY fixture, but I'm a little confused :S


The first variable is "Lumens per LED".. as I understand the first part help me to calculate the PAR level per LED... so... what If I'm thinking to have a combination of LEDs like Cool White + Warm White + Royal Blue and maybe some deep or far red, normally every color comes with a different lumen range.. correct me if I'm wrong but some variable like "Number of LED rows" is assuming the same type of LED?


Thanks in advance


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## Hoppy

The calculator is based on using white LEDs only, and they tend to produce about the same lumens for every version of white. If you add in a lot of red/blue, etc, LEDs the calculator won't give good results. This is an empirical calculator, not a theoretical one. It is based on using a variety of data and finding an equation which works well enough with all of the data.


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## plantbrain

Hoppy said:


> The calculator is based on using white LEDs only, and they tend to produce about the same lumens for every version of white. If you add in a lot of red/blue, etc, LEDs the calculator won't give good results. This is an empirical calculator, not a theoretical one. It is based on using a variety of data and finding an equation which works well enough with all of the data.


This is an inherent problem with LED calculations. 

The more light type variables you add, the messier things start to get. There's much less consistency since you can DIY so many options. 

Still, you can get reasonably close with the Whites, then go from there when you add say a set ratio of red and blue mixed with a % of the white. 

Say 10% blue, 50% red, 40% white. 

Seems that most of the blue types will be close to one another(I would assume), and likewise the same for the reds. 

You could add an estimation of those 3 variables without too much extra effort. Then real testing to see how far off the model is/is not. You need some data: averages of the reds and blues for that, then some averages on real fixtures to see how well the model works. If the averages are a bit off, you can then go back and add a correction factor to make up for that in the model.

A few step wise adjustments, I think it can work out fairly well to account for the other colors. Since many folks ALREADY have white/red/blue mixes in their fixtures, you just need some of their PAR data basically.


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## skanderson

one thing to add is that the new idea in reef lights is to add lime leds because the whites are low in that part of the spectrum. I think that a simple 4k/7k mix looks decent. the tank pictured below is a 65 hex with one 30 watt 4k bridgelux bxra and 4 3 watt cree 7k xmls for a total of 43 watts.
 its just a grow out tank in my fishroom but the plants are growing fast and coloring well.

Bump: wrong picture above that is of my frag tank and sump lit by only 4k bxras. the 65 hex pic is here.


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## Hoppy

If I wanted to try this calculator problem again I would use an empirical approach to get the PAR results for individual LEDs, then use a theoretical approach to get the total PAR for various arrays of those LEDs. It isn't easy to do this, but the results would likely be more accurate. But, I don't plan to do this, and I think several others have already done it. They just haven't made their results widely available and in an easy to use format.


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## ybendek

Hoppy said:


> If I wanted to try this calculator problem again I would use an empirical approach to get the PAR results for individual LEDs, then use a theoretical approach to get the total PAR for various arrays of those LEDs. It isn't easy to do this, but the results would likely be more accurate. But, I don't plan to do this, and I think several others have already done it. They just haven't made their results widely available and in an easy to use format.


Hoppy.... thank you so much for this tool, I understand ...


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## ybendek

Another question guys.... could this work good with cheap LEDs? I mean, for example other cool whit LED with 200 Lm.


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## Hoppy

It will work reasonably well as long as you have a good idea what angle to use as the optic cone angle, and if you have good data on the lumen output at the current you will be using. The cone angle is the hardest one to guess at unless you are using optics.


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