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Lighting was so simple when everyone used T8 or T5 fluorescent bulbs. All you had to account for then was the reflector quality. Now we have LED lights with hundreds of different things that affect how much light we get. I thought I could simplify lighting when I started working on it, but then LEDs came along and I gave up. Screw-in fluorescent bulbs are another variation that is very hard to simplify.

Before we can get much use from data reported by all of us we need to agree on how we measure the PAR that we say we have on our tanks. It is relatively easy to just use the PAR measured at the substrate, but that can distort our data sometimes. But, if we measure PAR at each plant, say near the middle of the plant, we get so much data it is even harder to make much sense of it. Then, there is the fact that those of us who used Apogee PAR meters got incorrect measurements because Apogee didn't realize that they needed a big correction to their in-water readings until a few years ago. (The readings were all about 15% low.)
 

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Discussion Starter · #22 ·
Here are the meager finding of my literature search:

Freshwater Biology (2015) Volume 60, Pages 929-943
Elodea Canadensis, Egeria Densa, Hydrilla Verticillata and Ceratophyllum Demersum were grown for 3 years under 100 μmol/(sec m2) at the water surface. Relative growth rate (dry mass increase per a day) increases 2-4 times with light increase to 150 μmol/(sec m2) at the water surface.

New Zealand Journal of Marine and Freshwater Research (1994), Volume 28, Pages 235-241
Lagarosiphon Major and Myriophyllum Triphyllum were grown under 200 μmol/(sec m2) presumably at the water surface (authors did not specify this) for 14 hours of light per day.

Aquatic Botany (2015) Volume 120, Part B, Pages 205-211
Egeria Densa, Hydrilla Verticillata, Lagarosiphon Major and Myriophyllum Triphyllum were successfully grown for 2 months under both of 172 μmol/(sec m2) and 69 μmol/(sec m2) average light intensities measured at 5cm below the water surface. Average daily irradiance was 6.97 mol/m2 and 2.79 mol/m2 respectively which corresponds to 11.2 hours of light per day.

Aquatic Botany (2013) Volume 110, Pages 31-37
For Myriophyllum Aquaticum light saturation occurs at 270-300 μmol/(sec m2). The plant was successfully grown for 3 months at both 280 μmol/(sec m2) and 85 μmol/(sec m2) adjusted 1cm above the water surface, with 16:8 h day/night cycle. The high-light growth was a little faster only with CO2 addition.

Plant Physiology (1976) Volume 58, Pages 761-768
Photosynthesis of Hydrilla Verticillata, Myriophyllum Spicatum, Ceratophyllum Demersum, and Cabomba Caroliniana was studied by immersing apical portion of the plants in a glass test tube and irradiating the tube with incandescent lamps, so, presumably, the given PAR values are measured at the tube's surface.
Hydrilla - Myriophyllum - Ceratophyllum - Cabomba
Compensation point, μmol/(sec m2): 15 - 35 - 35 - 55
Saturation point, μmol/(sec m2): 600 - 600 - 700 - 700
Irradiance required for 50% photosynthetic rate, μmol/(sec m2): 80 - 120 - 145 - 160

I can not open Plant Finder anymore. The message is:
Access denied for user 'aquaticplant'@'10.%' to database 'aquaticplantcentral_com_pf'
Is something wrong?
 

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Discussion Starter · #24 ·
I did not give up! I just got distracted with algae. It seems that by the choice of LEDs wavelengths it is possible to discourage Blue-Green algae, BBA and other red algae, some Green Spot... all those that use not only chlorophylls A and B for photosynthesis. But I got stuck looking for scientific names for common algae. I have access to scientific literature about LEDs and Algae, but all publications use scientific names only. So I created an algae list and have just posted it on the algae forum. Will you please look at this list and see if my descriptions correctly correspond to common names? Maryland Guppy?
 

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If it can be useful here the measured pars of different commercial LEDs are shown
https://www.ukaps.org/forum/threads...ihiros-led-par-data-the-power-of-light.43178/
(please remove the link if it's to possible to insert it)

But I have a question regarding the calculation of necessary Watt/gal of some post ago. With LED I usually consider lumen instead of watt; an inefficient LED usually has a ration lumen/watt of 70/80, an efficient one more then 120/130.
If I consider a normal LED with a lm/W ratio of 100 I will have with your formula a saturation point of about 230 lm/gal.
But normally a good LED light is between 150 and 230 lm/gal.
With watt the calculation seems correct (more then 3 W/gal for saturation point), using lumen it seems not correct.
Is there anything wrong with my reasoning?
 

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Question about PAR meters: Do they all measure the TOTAL light energy from 400 to 700 nm, or do some have the option of measuring energy in smaller intervals, such as 400-450, 450-500, 550-600, etc? If they only measure the full range 400-700 total, then 2 lights of very different quality could have the same PAR reading, for example a "good" plant light with strong red and blue peaks, versus a "bad" plant light with mostly yellow-green (500-600 nm) and insufficient red & blue. I'm sure this questions has been answered elsewhere, probably many times, but please forgive my lack of patience for seeking it out. Gerald
 

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Question about PAR meters: Do they all measure the TOTAL light energy from 400 to 700 nm, or do some have the option of measuring energy in smaller intervals, such as 400-450, 450-500, 550-600, etc? If they only measure the full range 400-700 total, then 2 lights of very different quality could have the same PAR reading, for example a "good" plant light with strong red and blue peaks, versus a "bad" plant light with mostly yellow-green (500-600 nm) and insufficient red & blue. I'm sure this questions has been answered elsewhere, probably many times, but please forgive my lack of patience for seeking it out. Gerald
PAR meters has one photo sensor that measures to the range of 400-700. You would need multiple photo sensors in one to parse the spectrum. You're right, it would treat yellow-green and blue-red similarly in readout.

I think plants do need small amounts of yellow-green to photosynthesize optimally though.
 

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The best PAR meters give equal weight to every section of the spectrum between 400 and 700 nm. The good enough PAR meters give close to equal weight to most of the sections of the spectrum between 400 and 700 nm. Most of the PAR meters we hobbyists have fit into the second group. But, some of the PAR meters in use virtually ignore the spectrum above 550 nm or so. No PAR meter is made to provide a record of the spectrum being measured. That requires a different meter.
 

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A spectrophotometer could parse out the different spectrum. I think there's a DIY spectrophotometer out there.
 

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Based on what you guys are saying, a PAR meter isn't sensing anything beyond what my eyeballs can do? 400 to 700 nm is the same range as visible light. Sure, a meter can assign a number in whatever units I want, which my eyeballs can't, but I can easily tell which of two lights looks brighter. A camera light meter would accomplish the same task. Am I missing something "special" about PAR meters?

EDIT: OK, I found a bit more info: our eyes respond best to the middle of the visible spectrum (yellow-green, 500 to 600 nm) and under-estimate reds and blues, whereas a good PAR meter is equally responsive to the full range.
 

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Discussion Starter · #33 ·
roby70:

Sensitivity of human eyes is maximum at 555 nm (in the green region), which is one of the worst wavelengths to grow plants. Lumen measuring is predominantly concerned with yellow/green regions of PAR.

Sensitivity of plants is maximum at 660nm (quite far in red), which humans can barely see. Optimal for plants seems to be 80% 660nm + 20% blue. This makes it possible to make a white LED light for aquarium, because you can have a lot of red for plants, but for the lighting to appear white to you, very little green needs to be added. I will be posting a lot of details, but the bottom-line answer for your question: you should never use Lumen to assess aquarium lighting.
 

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Thanks Bucha; looking forward to your additional details. "but the bottom-line answer for your question: you should never use Lumen to assess aquarium lighting." Yes, I realize a PAR measurement is a little better than a visible light measurement (Lumens), but if a PAR meter can't distinguish the important red & blue wavelengths from the less-useful yellow & green ones (all wavelengths 400 to 700 are lumped together) then the meter will still measure high PAR on a low-quality light (for plants) that's mostly yellow-green, correct?
 

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I know the best thing would be to know PAR and spectrum but in different case we do not have them. If we use standard LED we have an idea of the spectrum but we do not know PAR. So to undestarnd if a light is enaugh we have only watt or lumen.. it's not the good thing but probably the best that we have.

If someone have better method .... thanks for sharing them
 

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Human eyes are a very poor light meter. When we see a small difference in intensity, it is really a big difference. Our brain tries to adjust brightness so it looks "correct", so we can never trust it to show us what the actual brightness is. And, of course we are almost blind to red light, which is the dominant "color" in sunlight.

A couple of days ago I did some experimenting with my new LED light/dimmer combination. It reduces the intensity in steps, one step per click. I watched the light intensity my eyes saw vs what the PAR meter said. I could see the drop in intensity each time, but a couple of seconds later it looked just like it was before I clicked the dimmer. Only after I dropped the intensity in half could I clearly see a difference in the visible intensity. The next day I was curious about whether or not the dimmer would maintain the dimming after it was shut down overnight. When the lights came on I wasn't sure if it maintained it or not, until I used the PAR meter to verify that it did maintain the dimming. Our brains just aren't wired to make our eyes act as a light meter.
 

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I will be watching the results of any tests like this with great interest!
I will be wathcing too!
I have just finished my light and am very happy with results. But still have doubts. Only plant with problem is my Alternathera, which I have 8 years in same aquarium (old one, same ground, same fishs, same plants), and it was always most red in town, never problem... But the problem did not start with LEDs, but with neglecting aquarium care when I looked only on spectra aplication, which PSU, which optics, and such things. My CFL probably had lost their power, there was lack of CO2, I have not trim plants on time so Alternathera went to top, did not change water for weeks. And GDA come. Mostly affected are my red plants - Althernatera and M. Tuberculatum. I do not think that I will kill GDA just with light! Well, maybe with UV...

I have not PAR meter, I just see that all plants like LED light. Strong pearling, good coloration, except Althernatera.

You are much talking about PAR, right spectar and such things. But I believe that imitation of sun is best spectar. And this is changing during time of day, year, location etc. Too much things about how plants uses light is still unrecognized.

Our aquarium is for our eyes, so how to reconcile high PAR with high CRI, without promoting algae?
 

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In this video, growing lettuce, the white LED with lower PAR gave 37% more growth (by weight) than the red-blue LED with higher PAR. (Red-blue also produced more bitter taste; might be an advantage if you're keeping plant-eating fish!)

I accidentally found this.
white LED vs Red/Blue LED for plant growth.
 

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In this video, growing lettuce, the white LED with lower PAR gave 37% more growth (by weight) than the red-blue LED with higher PAR. (Red-blue also produced more bitter taste; might be an advantage if you're keeping plant-eating fish!)
Or turn people away from eating greens.
 
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