Lighting an Aquarium with PAR instead of Watts - Page 2 - The Planted Tank Forum

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post #16 of 445 (permalink) Old 07-22-2012, 11:51 AM
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Technology in aquarium has stepped up!
I still remember 2 years ago "watts per gallon" was still widely used.
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post #17 of 445 (permalink) Old 07-22-2012, 12:54 PM
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PUR = photosynthetically usable radiation, a concept I haven't yet seen a good reason to dig into. Plants use light from the whole spectrum between about 400 and 700 nanometers wave length. Unlike what many people believe, they also use green light, just not as efficiently as they use blue and red light.

If it was hard to get enough light to grow our plants, we would want to get every advantage we could, and look for bulbs that wouldn't waste any light in the green wave lengths, which, if you think about it, would leave us with very drab looking plants. But, the bigger problem we now have is avoiding too much light, not getting enough light. So, why bother with PUR?
I know your position on PUR measurements, so my suggestion was only half serious. I think your charts are a good general guide because all manufacturers of lights fairly much use the same three phosphors, the caveat, but in varying proportions even though they have access to as many as 20 I believe.


Let me present this argument why I feel PUR is important. A PAR meter measures all PAR wavelengths. It's a generalist's tool. The charts you have created do not plot PAR wavelengths vs. micromol, they show total PAR wavelengths in micromols. As you noted plants use green light and likely other wavelengths less efficiently. But other wavelengths most efficiently. How does one determine from the charts what specific wavelengths of PAR you are actually measuring for any particular light source ?
Knowing PUR vs. Distance could avoid this perhaps.
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But, the bigger problem we now have is avoiding too much light, not getting enough light. So, why bother with PUR?


Aesthetics (CRI) is another matter for a separate discussion.
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post #18 of 445 (permalink) Old 07-22-2012, 02:08 PM
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Cost of dividing watts by gallons? Price less.
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post #19 of 445 (permalink) Old 07-22-2012, 03:04 PM
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This is excellent info. I just wish more people of aware of this. Unfortunately a lot of people still go by "watts per gallon" some people think that the more "watts" they have the more "hi-tek" they are. They are very mid-informed.
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post #20 of 445 (permalink) Old 07-22-2012, 03:55 PM Thread Starter
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Aesthetics (CRI) is another matter for a separate discussion.
CRI remains a bit mysterious to me. Recently I read that incandescent light gives a CRI of 100 - perfect. That was because the color rendering index is designed so that perfect color rendering is that of incandescent light. I doubt that anyone reading this wants an aquarium to look like it has incandescent bulbs lighting it.

My first tank, back in the 1950's had an incandescent light, which I quickly replaced with a DIY T12 fluorescent light. I was amazed by how much better it looked with the fluorescent light, even though T12 bulbs, all that were available then, were notorious for making people look like ghouls.

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post #21 of 445 (permalink) Old 07-22-2012, 05:33 PM
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CRI remains a bit mysterious to me. Recently I read that incandescent light gives a CRI of 100 - perfect. That was because the color rendering index is designed so that perfect color rendering is that of incandescent light. I doubt that anyone reading this wants an aquarium to look like it has incandescent bulbs lighting it.

My first tank, back in the 1950's had an incandescent light, which I quickly replaced with a DIY T12 fluorescent light. I was amazed by how much better it looked with the fluorescent light, even though T12 bulbs, all that were available then, were notorious for making people look like ghouls.
CRI is a complicate subject but worthy of aesthetic consideration. I feel the target light quality should bare a close semblance to *noon equator sunlight. Most people would probably agree since most people choose a light source of 6500k.
With all the phosphors available for use, I wonder why lighting techs don't design a flourescent light source that has a better semblance to noon sunlight at the equator ? Thereby creating a light source with good PAR/PUR and good CRI. Perhaps it's just too costly for a small market.
Bulbs that have good CRI >90 are:
Giesmann 6000k Midday
Eiko's 5500K ColorMaster Digital bulb
Alzo's 5600K video bulb

*It seem to be around 5800K.

Last edited by Steve001; 07-22-2012 at 05:49 PM. Reason: x
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post #22 of 445 (permalink) Old 07-22-2012, 05:44 PM
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I believe the issue is the cost/ difficulty of making a high cri bulb versus the people who actually care for/ need one.

I believe a cri of 100 makes an object appear just as is would outside under the sun. I don't believe it matters too much for us, as we use whatever looks appealing to us.
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post #23 of 445 (permalink) Old 07-22-2012, 11:18 PM
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I'd recommend we "sticky" this tread.
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post #24 of 445 (permalink) Old 07-23-2012, 12:22 AM
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This is based on my own measurements, using brand new GE CFL 6500K bulbs, in 8.5 inch diameter reflectors. Larger reflectors will give lower PAR and smaller will give higher PAR.
Based on the threads I've read here the 8.5 dome lamp seems to be much more popular then samller one.

Is that because the 8.5 inch dome will give you a wider light spread then a 5 inch at the same distance?
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post #25 of 445 (permalink) Old 07-23-2012, 01:52 AM
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Excellent post and thread. My only suggestion would be possibly lowering the scaling on the CFL chart. It goes very high, and most people using CFLs are intetested in a PAR range of 10-100 or so ( from what I can gather).
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post #26 of 445 (permalink) Old 07-23-2012, 03:00 AM
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Great information! What is missing is a graph on LEDs. Thanks for all the time you spent gathering this info and then sharing it with us. I didn't realize that a less than $100 par meter option existed
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post #27 of 445 (permalink) Old 07-23-2012, 03:27 AM Thread Starter
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Based on the threads I've read here the 8.5 dome lamp seems to be much more popular then samller one.

Is that because the 8.5 inch dome will give you a wider light spread then a 5 inch at the same distance?
Yes, when the same amount of light is spread out over a larger area it has to be at a lower intensity, and vice versa.

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Excellent post and thread. My only suggestion would be possibly lowering the scaling on the CFL chart. It goes very high, and most people using CFLs are intetested in a PAR range of 10-100 or so ( from what I can gather).
Good suggestion! I changed it.

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Great information! What is missing is a graph on LEDs. Thanks for all the time you spent gathering this info and then sharing it with us. I didn't realize that a less than $100 par meter option existed
LED lights can't be treated this way. The variety of configurations is almost endless, so no simple charts can ever show much of value with them. However, it would be possible to put the most popular, most usable on planted tank ones on one chart. Keeping that chart up to date as more and more different LED lights become available would be a major chore. Maybe someone wants to convert the information in LED Lighting Compendium to this format? It takes a lot of time.

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post #28 of 445 (permalink) Old 07-23-2012, 05:46 PM
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I would be really interested in seeing the figures on common LED fixtures or even single LED stars put into more common terms than the link provided for the led lighting compedium. The charts Hoppy has created for the different lights and brands is easily understood.
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post #29 of 445 (permalink) Old 07-23-2012, 06:26 PM
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Why do you consider 50 PAR to be high light? I've read somewhere else that they say 100 is high! Maybe they're using different units/measurements.


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post #30 of 445 (permalink) Old 07-23-2012, 06:38 PM
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Why do you consider 50 PAR to be high light? I've read somewhere else that they say 100 is high! Maybe they're using different units/measurements.
PAR values are subject to change and based on the posters (Hoppy) experience... in this case Hoppy has a lot.

Another thing to consider is the PAR values are at the substrate, so if you have 50 PAR at the substrate you could easily have 150 at the water surface.

Lastly, it has been said by many people that if you have 50PAR at the substrate there isn't a plant you can't grow with proper CO2 and ferts.
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