# Calculating PAR?



## Sean W. (Oct 12, 2013)

Whats up guys,

I have 5 gallon tank just laying around, and I recently just took down a 22 gallon 18" cube tank that wasnt planted or anything, it was very unimpressive. I was just messing around with my spare fish stuff and it turns out the LED light hood i had on my 22 gallon tank fits perfectly on the 5 gallon. The light hood is the stock florescent fixture that i gutted and put three 20" Aqueon modular LED tubes in there, here is a link to the LED tubes.

http://www.petsmart.com/product/ind...=LIghting+&amp;+Hoods&f=PAD/psNotAvailInUS/No

I was thinking about making this into a high tech dirted tank, Co2, timers, the whole 9 yards and keeping demanding plants like Dwarf hairgrass or dwarf baby tears. But im not sure if this light would give me what i want on this little 5 gallon tank. Dont get me wrong its bright as hell, i think it would do a good job but im just not sure.

So i went onto the android play store and just searched " light meter " and installed an app that claims to measure light and i was wondering if it would be possible to calculate PAR from any of the measurements this little app gave me?

Here is a screen shot of the app with my phone in the tank and the light on:










a picture of the tank with the light on it:










and the light itself 











thanks for any input guys!


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## Zapins (Jan 7, 2006)

It is not possible to calculate PAR from other measurements it must be directly measured with an expensive PAR meter.

It is not necessary to know the PAR of your bulbs to grow plants. As long as the bulbs are fluorescent and enough wattage you should be able to grow what you want.


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## Greystoke (Jul 24, 2010)

Zapins said:


> It is not possible to calculate PAR from other measurements it must be directly measured with an expensive PAR meter.


That is only generally true, particularly for fluorescent lights. LEDs on the other hand are different because - unlike fluorescent lights - their spectra share a common shape, ie: a big bulk in the centre and a peak around 450nm, with intensities varying depending on the required Kelvin rating. 
This means that, within a certain degree of error, the Kelvin rating defines the spectrum, and when the spectrum is known all the LED's secrets are out.
Give me the Kelvin rating and the luminous output, and I will give you the PAR output.

Example: A 6500K LED with an output of 100Lumen will give you ≈1.3PAR output




Zapins said:


> It is not necessary to know the PAR of your bulbs to grow plants. As long as the bulbs are fluorescent and enough wattage you should be able to grow what you want.


Partially correct, but its stretching the truth.


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## rininger85 (Jun 30, 2013)

I don't know how truthful this is, but I just found this...

http://www.advancedaquarist.com/2008/2/review#section-4

if that's the case it would suggest I have 135 PAR in my work tank about 3-4" from the lights (not in the water since I just downloaded this same app to get my LUX which surprised me that it does seem pretty accurate, I have a 13W bulb that says its 860 lumens and an 18W bulb that says its 1260 lumens, the app says I have 10000 LUX, which would be about 929 lumens...) I'm not sure what that means I would have at depth, but I definitely doubt I have 135 PAR at depth because I'm running a low tech no CO2, and dosing excel once or twice a week (although I am dosing 5mL at a time in a 10 gallon tank, maybe I'm not low tech anymore at that point?)


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## Greystoke (Jul 24, 2010)

I generally agree with that info. "general" because the info applies to fluorescent tubes, in which case the conversion is tube specific and different from manufacturer to manufacturer (I can prove that with collected data)

Here in South Africa we don't work with PAR at depth, basically because we don't have PAR meters (I only know two fish hobbyists in the country that own a PAR meter :icon_sad. So we estimate what the PAR level should be at the water's surface given the PAR output of the light and the efficiency of the reflector. What happens to the light when it travels down the water column is anyone's guess, although the plants will tell you soon enough.


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## xmas_one (Feb 5, 2010)

I'd be willing to bet it's a lot less brighter than you think. I just built a 20w pendant and it looked super-insano bright, but the par meter said different. If you're willing to travel, we could test your setup with my par meter, or take it down to your local hydroponics shop, most of them have the apogee meters and are more than willing to help you out.


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## MarkM (Sep 16, 2012)

I bought a Par sensor and it works on my VOM. Still expensive but down to about a third of a meter. 

After I bought my sensor I found that my local club has a par meter and members can make arrangements to borrow it.


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## Sean W. (Oct 12, 2013)

rininger85 said:


> I don't know how truthful this is, but I just found this...
> 
> http://www.advancedaquarist.com/2008/2/review#section-4
> 
> if that's the case it would suggest I have 135 PAR in my work tank about 3-4" from the lights (not in the water since I just downloaded this same app to get my LUX which surprised me that it does seem pretty accurate, I have a 13W bulb that says its 860 lumens and an 18W bulb that says its 1260 lumens, the app says I have 10000 LUX, which would be about 929 lumens...) I'm not sure what that means I would have at depth, but I definitely doubt I have 135 PAR at depth because I'm running a low tech no CO2, and dosing excel once or twice a week (although I am dosing 5mL at a time in a 10 gallon tank, maybe I'm not low tech anymore at that point?)



According to that, if i use the Sunlight constant, this light gives me a PAR of 40... not ideal. I read that when measuring LED PAR, you use the "sunlight" setting on a meter.

I also have a hood that would let me screw in two regular bulbs into it. What compact florecent bulbs could i use to get me the high par that i want with out being nothing but an algae tank and bringing the water temp up to 95°?


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## xmas_one (Feb 5, 2010)

Duh, lemme grab that app and run it next to my par meter and I'll see if I can get a matching read.


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## Sean W. (Oct 12, 2013)

xmas_one said:


> Duh, lemme grab that app and run it next to my par meter and I'll see if I can get a matching read.


good idea!

i just searched " light meter " and installed the top one


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## xmas_one (Feb 5, 2010)

Maybe my phone is weird I could only get lux of 7, 75, 1000, 10000, and 16000.


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## Sean W. (Oct 12, 2013)

Can anyone point me in the direction of what would be a good CFL bulb to use two of in the other hood i have for this tank. It can take two regular screw in bulbs, i dont think i want to just go with the brightest ones i can find, i think that would be too much light. thanks!


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## UDGags (Sep 13, 2009)

Greystoke said:


> Example: A 6500K LED with an output of 100Lumen will give you ≈1.3PAR output


Then you have optics, reflectors, water, etc. to factor in right?


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## Greystoke (Jul 24, 2010)

UDGags said:


> Then you have optics, reflectors, water, etc. to factor in right?


It's the virgin output of the LED only.:icon_bigg



xmas_one said:


> I'd be willing to bet it's a lot less brighter than you think. I just built a 20w pendant and it looked super-insano bright, but the par meter said different. . .


You may be right about that, but we do quite well without PAR meters. They're just too expensive and by now we've learned to gut-feel the water losses.


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## boxboy (Jun 1, 2013)

I downloaded this app too. I will post results tomorrow when lights come back on.
currently using a par38 18w 120° beam.


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## anastasisariel (Oct 4, 2009)

Well, regardless of whethe or not PAR can be calculated with that app, I still think I may have a use for it.


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## rininger85 (Jun 30, 2013)

If you want to read up on the CFL bulbs check out the link in my signature... there is some really great info in that thread, I think the tank that was used for an example is a 2.5gal so a bit smaller, but I used the info in that thread to decide to run a 13W and an 18W spiral CFL bulb in my 10 gallon work tank and I'm getting some pretty amazing growth... I had some algae in it, nothing that ghost shrimp and a gold algae eater didn't take care of though. I do have some algae growing on the glass, but its not terrible. Check my 10 gal planted dirted work tank link, I posted progress pics in there for reference.


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## boxboy (Jun 1, 2013)

Just tried this app... held the app 6" from light source 18w par38 120° beam angle, 6" is right at the water line for my tank and the app says I got 9000LUX...


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