Quote:
Originally Posted by Hoppy
The water absorbs almost none of the intensity at these depths, and actually tends to focus the light due to the refraction at the surface. I suspect and my data indicates that there is very little difference in the intensity whether the water is there or not.
|
I respectfully disagree with this statement. By using the meter, I have measured a loss of about 20 umols/m2/s just by measuring immediately above and below the water surface. Whether this is due to a lens effect, surface reflection, or simple absorption I'll leave open for debate. But there is a significant loss due to the water. I can follow up with more precise measurements when I return from my trip.
Quote:
Originally Posted by Hoppy
We don't really need to know the exact PAR value, just a good approximation.
|
I think even with the meter, you're only getting an approximation of PAR to start with. In the realm of quality spectrometers, the meter I use is a lower quality meter. So why approximate it further than that? If we attempt to do that, we're just back to the same problems associated with using watts-per-gallon as a metric for photosynthetic energy. Too much guessing.
Quote:
Originally Posted by Hoppy
... [Good approximation of PAR] - Even that is hard to do, with all of the variables involved.
|
Precisely - that is the main reason for my involvement in this thread. I wanted to illustrate that you can't take someone else's setup and apply it to your situation with out accounting for all the variable factors. Or, put another way, you can't get a good approximation of PAR values unless you attempt to duplicate, in every aspect, the setup that produced those PAR values.
I originally set out to answer AirSong's original question of how much light she needed over her 2.5gal aquarium. But I worked backwards... I duplicated
her setup and showed what kind of PAR she could get out of it by varying distance and bulb wattage.
Unlike most, you have an ability to correlate data mathematically to show trends; which allows you to extrapolate the data and make further assumptions so that you can apply it to a different situation. But, I suspect that most of the hobbyists here find that pretty daunting. And ultimately, it pushes them away from what PAR is and why it's better to use when discussing lighting for plants. It doesn't have to be that complicated. In my opinion, the mechanism of a simple meter reading is the only way PAR will ever be embraced by hobbyists, not through log plots and approximation functions.
The results presented in this thread will help people that want to set up something similar to AirSong's setup, using the same size tank, and the same type of light fixtures and bulbs. I just provided a few extra variations showing how easy it is to affect the photosynthetic energy provided to the plants.
Cheers!