# Tropica article PAR to Lumens



## Soilwork (22 Nov 2016)

Tom Barr mentions an article by Tropica where they converted PAR to Lumens.  Does anyone know where I can find it?  

Is PAR to Lumens calculation common knowledge? 

I'd be interested to find out as my LED is in Lumens.

Thanks.


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## zozo (22 Nov 2016)

I vaguely remeber reading this article. But it still doesn't reveal much to compair light sources with eachother.. It is very difficult without proper and rather expensive equipment. 

Even lumen is a rather old measure, since one lumen equals the amount of light emitted by one candle that falls on one square foot of surface located one foot from the candle. It's the same old cr*p as Horsepower which nowadays is converted to Watt, but it still tells us zip if you do not have the propper equipment to get a decent number.
It only says one is stronger then the other, but how strong?? Who knows, i guess even the sales manager in the shop only can say "Pretty strong!!"

Industrialy LEDs are measured in mcd (MilliCandela) this because leds do not radiate light all around like a bulb or tube does, it bundles the light in one direction. Now there is a rather complicated relation between Candela and lumen and lux in Luminous power per unit solid angle, which doesn't realy make it any easier to understand. It can be converted with a formula and just to make it more marketable the industry puts a lumen on the leds to give us a feeling we know what we are buying. But because it radiates light in a fairly different way than a bulb or a tube it stays a rather bad comparison.

Also in colors (kelvin) it deviates a lot with what material in the led is used to reach a certain spectrum.. All white leds are basicaly blue with a phosphor coating to make 'm radiate white light. The quality and origine of the phosphor determines in what range this white will be. I have a few leds in use which had in specs 10.000 k, but radiate a pinkish colored light while in general one would expect it to be more blueish. Since it basicaly is blue it probably is in the type of phosphor they used which makes it pink. 

I guess in the end, the best and cheapest par meter available to us are the plants.. Go with what they tell you..

I'm using leds above all my 3 tanks now, i didn't go for any ready made lfs product because the led industry changes to fast.. It's a new technique and they still charge to much development costs and you pay more for design then for light. So i made them myself and bought the strongest i could find with a dimming option. To much is always dimmable, not enough is extra expenses. For now and for what i grow under them it is sufficient.. i got 2 tanks which both regarding specs should have far over 5000 lumen of led power, which i doubt is true.. But can it be beter than sufficient??


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## zozo (22 Nov 2016)

Oh and sorry for beeing actualy a bit off topic on the initial question.. PAR is photosynthetically active radiation, this is measured between 400 and 700 nanometer which plants can use for photosynthesis, i doubt there is a true lumen x par conversion, since lumen says nothing about the wave band. 

But there is a scapefu podcast with an interview with an Horticultural light expert.. Stating plants grow with any (white) light visible by the human eye..


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## Soilwork (22 Nov 2016)

Thanks for your input Zozo.  I'm ok with the fundemtals of PAR.  I don't care too much with Kelvins, CRI or even wavelength as I know that if the light is visible white light plants will grow.

I'm not familiar with LED technology though and how this translates to other light emitting technology so that was insightful.

The thread I refer to is here:
http://www.barrreport.com/forum/barr-report/lighting/7629-brighter-light-shorter-photo-periods/page2

Was wondering what Tom actually meant.


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## rebel (22 Nov 2016)

Soilwork said:


> The thread I refer to is here:
> http://www.barrreport.com/forum/barr-report/lighting/7629-brighter-light-shorter-photo-periods/page2


I think he's saying that until you measure you light, you can't say whether it's high or low.


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## zozo (22 Nov 2016)

If i rememer correctly their is a thread here at ukaps linking to this Tropica article also an in depth discussion about PAR readings etc. That's how i ended up there i think... I truely most say the whole concept goes beyond my understanding with all the jugling with numbers, abbriviations and formulas. That's probably why i think to remember it vaguely. As Tom states it was conversible to lumens back and forth in their case, probably knowing what lights, the specs and how it relates to eachother. I doubt that lumens is all you need to make that conversion. What i understood from the whole story, you just can't and need proper equiptment to measure par at the substrate level to get a number.

I also remember an article on the website of TGM from maybe bit more then a year ago advising strongly against the use of leds and said not selling led lights in their shop because they didn't yet have satisfiyng results with what was available at that time.. It only took a few months and the article was taken down from the web site and they started selling led light fixtures and even using them too.. It is that fast how led industry develops and still is. So that would make about everybody evenly unfamiliar with the use of leds above an aquarium, before you think you know something there is something new and even beter developed..

I guess it's the led industry which threw the whole lumen per gallon and or watt per gallon out of the window. It all doesn't fly anymore.. What flies at the moment is indeed still luminous power of the source and the wave band still reaching the plants at substrate level for which you definitively would need an electronic (waterproof) device to measure. Where depth and color of the water column per tank will have an influence.

Imho i believe the whole PAR concept is a bit overrated enterpreted in the hobby.. It might be of importance for the (professional) hipster aquarist trying to blow away the competition with lusher than lush and redder than red.. But for the average hobbyist it will just stay abracadabra.. And if it was so easy and cheap to determine it would have been on the box of any aquarium lamp available by now.. And indeed as said, since plants grow under any vissible white light it probable contains the par it needs already enough.

Even the whole lumen in led industry is a bit vague and i have still no idea how this is determined if you do not measure it with the proper equipment after a light is build. Since with leds it is an array of small light sources which if you buy the components the manufacturer gives the luminous specs per source e.g. 65 lumen per chip. If this compaires to  650 lumen per 10 chips i have no idea.  I have 4 led strips above a tank which has 144 leds of 65 lumen per led in reality i have no idea what i have. Only that it is much more then sufficient and need to hang it 40 cm above the tank at 100% or dim it.

The only thing what i think to know, because i red it in an scientific article, is leds nowadays cover a wider spectrum then any other lightsource available. So if that's the case, i have more power then the tank can take and i indeed see my plants grow very nice why should i worry about a par number..


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## Soilwork (22 Nov 2016)

Ok thanks.  I do understand your points.  I was literally just wondering if PAR to Lumens had anything solid behind it.  I know how difficult it is to interpret our light intensities and I seldom worry about it.  I just saw this and was wondering if I had been left behind somewhere along the lines.


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## zozo (22 Nov 2016)

Here you have a example of this formula under Yield of photon flux.
https://en.wikipedia.org/wiki/Photosynthetically_active_radiation


> For example, a light source of 1000 lm at a color temperature of 5800 K would emit approximately 1000/265 = 3.8 W of PAR, which is equivalent to 3.8*4.56 = 17.3 µmol/s. For a black-body light source at 5800 K, such as the sun is approximately, a fraction 0.368 of its total emitted radiation is emitted as PAR. For artificial light sources, that usually do not have a black-body spectrum, *these conversion factors are only approximate.*



Then in an aquarium you still have to take the filtering propperties of the water into account.  

A year ago i looked at Apogee instruments, i forgot the price but quickly skipped back to something more fun to watch..


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## jameson_uk (22 Nov 2016)

Soilwork said:


> Tom Barr mentions an article by Tropica where they converted PAR to Lumens.  Does anyone know where I can find it?


It could be http://tropica.com/en/guide/make-your-aquarium-a-success/light/ but that doesn't mention specifically mention PAR.
It does talk about photon lux which looking at (http://www.thereeftank.com/forums/showpost.php?p=1573493&postcount=2) is the same thing?


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