# Lighting levels by Lumen??



## Mxx (Dec 29, 2010)

Would anyone happen to have any sort of chart or equation to figure out how to determine Low/Medium/High light levels by lumen in relation to tank depth/size? (Instead of by watts which aren't very applicable to LED and other lighting).


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## llamas (Jul 5, 2010)

http://www.plantedtank.net/forums/lighting/105774-par-vs-distance-t5-t12-pc.html


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## Mxx (Dec 29, 2010)

llamas said:


> http://www.plantedtank.net/forums/lighting/105774-par-vs-distance-t5-t12-pc.html


I saw that chart, but had no idea how to apply that to the lights which I'm looking at, which are rated in lumen...


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## Hoppy (Dec 24, 2005)

Lumens are the total amount of light emitted by a bulb, in all directions. Knowing how many lumens a light emits does you little or no good. We need to know how much light reaches the substrate, the farthest point from the bulbs. And, that is measured in PAR, which is light as sensed by plants, while lumens are about light as sensed by a human. The equivalent of PAR in the lumens system of measuring is Lux.


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## Mxx (Dec 29, 2010)

Hoppy said:


> Lumens are the total amount of light emitted by a bulb, in all directions. Knowing how many lumens a light emits does you little or no good. We need to know how much light reaches the substrate, the farthest point from the bulbs. And, that is measured in PAR, which is light as sensed by plants, while lumens are about light as sensed by a human. The equivalent of PAR in the lumens system of measuring is Lux.


Okay, complicated... The LED's that I'm working with have a relatively focused beam and are described by lumen instead of PAR, so they lumens would be helpful if I had a gauge with which to compare, but I'm not sure if there is any way for me to make a comparison between PAR and Lumens and Lux in that case?


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## llamas (Jul 5, 2010)

Oh, I see what you are asking now.. Sorry about the useless info.

Unfortunately, I don't know the answer to this either. Have you searched how to determine lux based on lumens? Maybe you can use the search feature on the forums and see if you can find any posts that may give you some answers..

Sorry that I couldn't help, Good luck!


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## llamas (Jul 5, 2010)

Maybe this will help? :icon_conf

http://www.plantedtank.net/forums/lighting/29224-how-find-lumens-lux.html


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## Mxx (Dec 29, 2010)

llamas said:


> Maybe this will help? :icon_conf
> 
> http://www.plantedtank.net/forums/lighting/29224-how-find-lumens-lux.html


That thread was helpful actually. With the focused light of LED's I can probably assume that almost all of the of lumen are focused upon the bottom of the tank and therefore received by the plants. (In my current small trial tank I certainly don't see much spillage, especially as the light which hits the sides of the tank is below the angle of incidence and therefore is generally reflected downwards within the tank. 

And therefore it should just be a matter of dividing the lumens a fixture would produce by the tank's bottom area measured in square metres. 

'Medicineman' had reported on that thread the light requirement of different plant species, which ranges from 500 lux to 200+ lux, so the low/medium/high light levels should break down along those lines, of 500-1000 being low, 1000-1500 being medium, and above 1500 - 2000+ being high. 

Here is his listing copied for reference: 
_500 lux : Cryptocoryne nevii, wendtii, afinis, java moss 
500-1000 lux : anubias nana, aponogeton madagascariensis, echinodorus sp, sagittaria sp 
1000-1500 lux : aponogeton sp, bacopa caroliana, egeria densa, ludwigia sp, marselia sp, ceratopteris thalictroides, java fern 
1500+lux : cabomba sp, hygrophylla poliserma, limnophila aquatica, myriophyllum sp, riccia fluitans, vallisneria sp 
2000+ lux :cabomba furcata, rotala macrandra _

If that is all correct and I suppose that might answer my question. Do those numbers as low/medium/high ranges seem to make sense to people?


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## Hoppy (Dec 24, 2005)

Because our eyes are not sensitive to red or blue light, compared to their sensitivity to green and yellow light, and because lumens are a measure of intensity as sensed by human eyes, you can't express plants' light needs in lumens or lux. PAR is the measure of light as used by plants. Two bulbs could produce the same lumens, but have big differences in PAR. That's one reason why some "plant bulbs" look dim compared to regular bulbs.


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## Mxx (Dec 29, 2010)

Hoppy said:


> Because our eyes are not sensitive to red or blue light, compared to their sensitivity to green and yellow light, and because lumens are a measure of intensity as sensed by human eyes, you can't express plants' light needs in lumens or lux. PAR is the measure of light as used by plants. Two bulbs could produce the same lumens, but have big differences in PAR. That's one reason why some "plant bulbs" look dim compared to regular bulbs.


I thought there might be some sort of approximations which you could assume if you knew the spectral composition of a given light source, but in researching lux further, it turns out that its measure is weighted according to the luminosity function which peaks around the green wavelengths, and therefore give a very very different representation certainly than PAR does, as you'd stated. 

I suppose you could still use lux as a rough guide if need be, as long as you know your light sources do have an appropriate spectral composition though, despite that it's far from an exact science. (Or for it to be an exact science would require quite a significant amount of calculus calculations across the entire spectrum of visible light!). 

Unfortunately the lights that I'm looking at such as LED's don't necessarily give a PAR value, so in configuring a lighting set-up PAR values aren't necessarily that much help. Perhaps I don't need precise figures though, as long as I can get an idea that I'm in the right range of intensity that I'm targeting. 

You had some great research on light intensity versus tank size and depth as well, which I'm still to get through, but I appreciate that you've delved into that parameter in such uh... depth.

By the way, anyone happen to have have any views on what they think the ideal spectral distribution of light would be for a planted tank, to achieve good plant growth, look perfectly natural with good colour rendition throughout, and not cause excessive algae? In looking at the spectral distribution of LED's light versus sunlight, the LED's seem to actually output a spectrum of light more suited to plant growth than sunlight itself is composed of.


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