Ok, here I am!
I spent about 30 minutes testing the Photone app with the LED full spectrum option, and the results are NOT good. I am sorry. I set the app in "PAR Meter" mode with the "LED Full Spec" set at the bottom, and the numbers I read, compared to the Apogee, are the following:
Apogee: 80 PAR (my tanks substrate) -----> App: 16
Apogee: 100 PAR -----> App: 21
Apogee: 150 PAR -----> App: 23
Apogee: 200 PAR -----> App: 28
I really can't make sense of it. I put the app and the meter in the same exact position with the same angle relative to the light. I have noticed that the Apogee is much more stable, and I mean, even if you change the angle a little, it doesn't change the value much (+-10) but the app can drastically change the result if you put it in a different angle, which doesn't make sense (+-30). Also, it is very unstable; sometimes I read crazy values by moving it, I read a few times values around 400 PAR when the Apogee measured just 100. It is very unreliable and, in my opinion, completely unusable. I am very sorry. It is also true that the app shows a warning that says "Diffuser Required," which could maybe improve the results. But I have no idea how much. But I certainly wouldn't spend money for a diffuser since, as you can read below, I think a PAR meter is absolutely NOT necessary.
I find the Light Calculator on rotalabutterly.com to be much more precise:
Planted Aquarium Light Calculator
rotalabutterfly.com
If I enter my tank's values, I get 76 PAR at the substrate, which is not too far from the 80 I read with the Apogee.
Please, see below my answers to your questions, in context:
I used Photone and purchased the LED full spectrum option.
The first would be to understand what do you expect from your PAR meter, and how are you using it.
- How often do you use your PAR meter?
Almost never. I bought it when I was trying to understand if I had too much or too little light 10 years ago, but I haven't used it ever since. Some friends asked me to borrow it once in a while, though
I would probably use it if I were changing the landscape or setup of my tank. But otherwise, I would not recommend buying it. It is much better to use the online calculator I mentioned above. And other reasons are explained below...
And, of course, I used it to find the perfect spot for my Orchids
- How many locations in your tank would you check?
If you had a PAR meter, I would recommend checking the bottom first, in 9 locations:
left-back
center-back
right-back
left-middle
center-middle
right-middle
left-front
center-front
right-front
That way, you can understand if your light is consistent through the tank. In my case, my PARs go down a great deal at the sides, so I know to put low-light plants in there
You might also want to measure about 3 inches from the surface, just to have an idea of the "light curve." If you see the curve being too steep (for example, 80 PAR at the bottom and 200 PAR at 3 inches from the surface), you may want to try to screen or lower your light so to have something like 60 PAR at the bottom and 120 at 3 inches. But the situation may vary a lot according to the layout, other plants, wood, rocks, etc. But I wouldn't be that paranoid unless you like to play and tinker with that stuff... as I said, I would not recommend spending $300+ for a PAR meter, it is actually NOT needed if you use the online calculator and you aim for 60-80 PAR at the substrate, you can go up to 100 or more if you want really strong light. That's a good starting point, and the rest of the measurements don't make much difference IMO.
- How accurate do you want to know your PAR number, could you live with +/- 5%, +/-20% or even +/-50%?
Well, I wouldn't go over 20%. For example, if you have an actual PAR measure of 80 at the substrate, and your meter gives you 60, that'll be ok anyway. But if you have 80 at the substrate and you measure 40, you will want to increase your light to aim for 80 at the substrate, when in reality, you could have 100-120, which could be much more light than what you'd want, and such a difference would make a huge difference in plant growth and, mostly, plant demand.
- In your view, how does PAR help you to understand and optimize your planted tank?
I think it can be used to "learn" and "understand" how light reaches your plants and how much that can vary according to your layout, location, etc. But once you understand that, the same will apply pretty much to any tank setup, and you'll know already to avoid putting plants that need more light on the sides or at the bottom covered by other plants, etc... often good sense corresponds to what you learn from using it
- Why is it that Reefers talk much more about PAR than planted tankers?
I think because of coral, but I don't know anything about reef tanks (!!!), I guess the video posted above could help with that
There are several YouTube videos for Reef tanks (with Reef tank lighting spectrum) comparing a dedicated PAR meter with an IPhone App. I can’t comment on the quality of these, or whether some may be sponsored/less objective. It would be helpful to have some comparison data for planted tanks
- Compare Apogee PAR measurement with iPhone app for planted tank, with ‘full spectrum LED’ selected as light source.
Yes, I answered this at the beginning of this post.
- What is roughly the % difference between Apogee and iPone App, and is this an acceptable accuracy for you?
Too much, as I read above, I measured 80-100% differences. Not good...
- When you change the color spectrum of your lighting (assuming your light source can do that), will you find the same accuracy for the Apogee compared to iPhone App?
I noticed no difference, I got the same skewed results.
Overall, if we assume that PAR measurement will be both cheap and easy, how much would these contribute for planted tanks?
Well, if it were cheap and easy, I would say that could give a good starting point for choosing and setting up the correct light for your situation. I'd say, if you'd want a low-light, low-maintenance tank, aim for 30-40 PAR max at the substrate, with peaks of 100 at the surface. If you'd want MID light, aim for 60-70 at the substrate, with peaks of 120-150 at the surface. If you'd want HIGH light, you can start from 90 at the substrate, and have 200 or more at the surface. More light ---> more growth ---> more demand ---> more work
Perhaps it is too much to ask you all these questions
@fablau , but hope that others may chime in as well to educate me. I have really no experience with light measurement.
It's never too much! I hope this helps, and please let me know if you have any more questions or doubts.
All the best,
Fab.
dominikmaglia.medium.com
growlightmeter.com
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