# PAR vs Column height vs Light height



## Edward (Apr 11, 2005)

While testing Light Calculator v1.2.2 Rotala Butterfly | Planted Aquarium Light Calculator, I made a chart from the results of light intensity increase on plants growing of the substrate to the surface at 2” depth dependent of light fixture installation height and aquarium height.

90 gallon 24” high and 10 gallon 12” high,
PAR 100 at substrate, PAR at 2” depth, light fixture installation height from 1” to 16”.

I think the results are explaining why it is easier to grow plants in smaller aquariums. For example, the growing top of plants must adjust to PAR from 100 to 1343 in 10 gallon aquariums, while the same plants from 100 to 5869 PAR in 90 gallon aquariums when light fixture is 1” above water. This is 13x more PAR in smaller aquarium versus 60x in larger aquarium. 

When light fixture is 6” above water, PAR increases from 100 to 401 for 10 gallon aquarium and PAR from 100 to 1227 for 90 gallon aquarium. This is 4x more PAR in smaller aquarium versus 12x in larger aquarium, still fairly significant increase.


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## Edward (Apr 11, 2005)

Also, I wanted to show how difficult it is for plants to keep adjusting to increasing light intensities when growing closer to the light source. This increases with larger aquariums and closer light installations. 

Noticed how high mounted lights are on larger ADA aquariums? 
The impact becomes negligible over 5” on 12” high aquarium and 15” on 24” high aquarium, both 4.7x increase from substrate to 2” bellow the waterline.


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## burr740 (Feb 19, 2014)

That's a great observation


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## Greggz (May 19, 2008)

burr740 said:


> That's a great observation


Agreed.

A taller tank has a wider range of PAR water line to substrate.

In my tank, it's about 280 to 110. In a shallower tank, this will be a smaller range. 

I think in general things would be easier in a shallower tank, as keeping foreground plants and tall stems happy is a little trickier in a taller tank. 

As a side note to you Joe, Edward and I have been talking and I think his 300 PAR at the substrate is legit. Crazy number, I could never get away with it.


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## jeffkrol (Jun 5, 2013)

hmmm.. Many of our plants are more than capable of surviving full sunlight as emergent plants.. 
https://www.petcha.com/15-emergent-growth-aquatic-plants-for-your-aquarium/
around 1600 PAR...
http://micahwoods.typepad.com/.a/6a00e553d5d110883301b7c882d67d970b-800wi
86,400 LUX..
465,000 Lumens over 2 sq feet..
Daylight factor of 54 

considering the above.. not sure how you get 6000 PAR............... 
That's 324,000 LUX....(using Apogee daylight factor)
https://www.rapidtables.com/calc/light/lux-to-lumen-calculator.html
https://www.apogeeinstruments.com/conversion-ppfd-to-lux/

Really have some issues w/ that calculator but can't quite put my finger on it..

http://www.melevsreef.com/pics/08/03/par_0322_new_bulbs.jpg

400W (approx 36,000 Lumens) MH and 2 t5ho's (?) and your water surface PAR is 970...


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## Edward (Apr 11, 2005)

Jeffkrol,
It will help if you think of the PAR numbers as light intensity percentage.


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## Greggz (May 19, 2008)

jeffkrol said:


> considering the above.. not sure how you get 6000 PAR...............
> That's 324,000 LUX....(using Apogee daylight factor)
> https://www.rapidtables.com/calc/light/lux-to-lumen-calculator.html
> https://www.apogeeinstruments.com/conversion-ppfd-to-lux/
> ...


Yeah I agree. 

Something seems off. 6000 PAR 2" below the water line doesn't seem right at all. Mine is 280 with T5HO. Funny thing is the PAR at substrate depth seems to be well within reason.

But the general concept still makes sense and is interesting food for thought.


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## Edward (Apr 11, 2005)

Greggz said:


> Something seems off. 6000 PAR 2" below the water line doesn't seem right at all. Mine is 280 with T5HO. Funny thing is the PAR at substrate depth seems to be well within reason.
> 
> But the general concept still makes sense and is interesting food for thought.


 Yes, but your light source is not 1” above water and the light reflecting of the top reflective material is much farther than the actual bulb. What value does your light meter read when you stick it directly to one tube? I imagine this would be very different with a spot light like LED and MH.



Greggz said:


> Something seems off.


 As for the calculator, I don’t think it is taking in consideration the area size of the actual light source. This may create distorted levels and the discrepancy between flat source such as T5 and spot sources such as LED and MH intensities when calculating very short distances.


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## jeffkrol (Jun 5, 2013)

Edward said:


> Jeffkrol,
> It will help if you think of the PAR numbers as light intensity percentage.


"substrate depth" is the thickness of the growing layer.. check
tank "depth" is "width"
tank "depth" x "length" is used to calculate "sq m"
adding a Lumen/watt number doesn't change PAR be it 20 or 1000L/W..so what is the point?



> 100 to 5869 PAR in 90


That is impossible.... 










Comparison:


> * MIXING LIST----------------------------------------
> Cree XM-L CoolWhite (5000-8300K) [120°] x12
> ----------------------------------------
> * SIMULATION DATA
> ...





> PAR is photosynthetic active radiation. PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis (*Figure 1*). PAR is a much used (and often misused) term related to horticulture lighting. PAR is NOT a measurement or “metric” like feet, inches or kilos. Rather, it defines the *type* of light needed to support photosynthesis





> *PPF* is photosynthetic photon flux. PPF measures the total amount of PAR that is produced by a lighting system each second.





> *PPFD* is photosynthetic photon flux density. PPFD measures the amount of PAR that actually arrives at the plant, or as a scientist might say: “the number of photosynthetically active photons that fall on a given surface each second”. PPFD is a ‘spot’ measurement of a specific location on your plant canopy, and it is measured in micromoles per square meter per second (μmol/m2/s). If you want to find out the true light intensity of a lamp over a designated growing area (e.g. 4’ x 4’)


Just noticed another oddity.. light distance from water line could be 50% of ";height" or any number..
for the above I "assumed" water = tank lip..


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## SingAlongWithTsing (Jun 11, 2015)

Greggz said:


> Agreed.
> 
> A taller tank has a wider range of PAR water line to substrate.
> 
> ...


idk, 300 PAR seems really tempting


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## Greggz (May 19, 2008)

SingAlongWithTsing said:


> idk, 300 PAR seems really tempting


Do it!

I would LOVE to see what happens. 

I would do it myself but frankly I'm too scared!:grin2:


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## SingAlongWithTsing (Jun 11, 2015)

Greggz said:


> Do it!
> 
> I would LOVE to see what happens.
> 
> I would do it myself but frankly I'm too scared!:grin2:


I'd do it if the electric company didn't charge me $0.18 per kwh LOL

i think rajkm over on barrreport is running his SBReef's at full 100%, dunno how high he hung em though. If I did that on my tank I think I would get 266 PAR. 
https://barrreport.com/threads/my-tanks.16009/


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## jeffkrol (Jun 5, 2013)

Greggz said:


> Yeah I agree.
> 
> Something seems off. 6000 PAR 2" below the water line doesn't seem right at all. Mine is 280 with T5HO. Funny thing is the PAR at substrate depth seems to be well within reason.
> 
> But the general concept still makes sense and is interesting food for thought.



Had to check w/ a "real" light.
Using a 35W COB running at about 17.5W and using a Seneye (out of water) I got 2176 "PAR"...
at about 1 1/2" using a INS dx-200 I pegged the Lux (limit is 200,000) but could get it in that range w/ a slight raise..to approx 2"


That would translate to about 3000 PAR w/ a large margin of error..
By 3"(sensor to COB distance) you are down to 100,000 LUX and 1" "over" 50,000 LUX.. 



results were about the the same for 2 different chips (SORRA, Luxeon FF)



Even getting 2000 "PAR" over any appreciable surface area would take an insane amount of light..

5" wil give you 300PAR..w/ a 17W COB..

https://www.nano-reef.com/applicati...9d02696e85dc5e6d10669b793fd32c6a980b81c2e7a81

https://www.nano-reef.com/forums/to...r-t5led-hybrid-with-par-measurements-as-well/


> OK, here are the PAR measurements of my ATI Sunpower HYBRID 5x24watt T5 and 24 Cree LED's @ 700mA (approx 60watts). 20 of the LED's have 80degree lens, the remaining 4 have 60degree lens.
> 
> 
> 
> T If I mount it lhe tank is 18" tall, 30" long and 20" front to back. The water height is 16" from top of sand to water surface.





> The light unit is suspended 7.5" above the waters surface. If I mount it lower, PAR levels get too high causing bleaching due to photoinhibition.


you only need 400-ish Watts for a 20" depth.. 
http://www.reefcentral.com/forums/showthread.php?t=1965294

7 Luxeon fresh fish COB's lensed at 90 degrees would do it.. for 24" tank..


> * MIXING LIST
> ----------------------------------------
> myData fresh-fish-v2.csv x7
> ----------------------------------------
> ...


Only about 200 real Watts...

30 x 30 x 30 centimeters..You can hit 300 w/ only 90 Watts..
http://sgreefers.com/threads/par-measurement-services.1519/page-2


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