Now add some plants, some water, some canopy over time and space.
Inverse square law is pretty much what we'd predict to find.

However, in the real world, it deviates.
So measure that afterwards once you are done here.

Measure, mark and follow a single leaf through a week or two, or a set of leaves(say 11 at random points in the tank). Plants will also adapt readily to light SFD as well as PAR and also through time/space.

Measure the effects of pruning weekly vs every 3 weeks.
Measure the effects of a MH vs a FL tube, spacing in FL tubes(say a narrow band with two bulbs near each other vs 15" apart).

As you can quickly see, you have an infinite set of possible questions to ask and test for there, and with respect to each plant species available (300-400).

Sounds great! I only spent all day on the first little problem, and I figure I have about 10 more possibly good years left, so I should be able to complete all of that. Can I keep the PAR meter for 10 years? Will the battery last that long?

However, I see the problem, just as I get down to the last question, someone out there will think of 10 to 100 more good questions. Not to speak of all of the new plants that show up every year.

Here is some more data from today's PAR measurements. The first is the meter readings along the length of the tank, at two distances from the bulbs: (10.25 inches is about at the substrate)


Then, the meter readings from front to back at two distances from the bulbs:


Look at how much the intensity drops off in just 6 inches!

Great work Vaughn! I can already begin to form a mental scape of the light distribution in the tank. Nothing very unexpected in your results so far except it is quite evident how much of a drop off in intensity there is with height! Btw, are all your data points at the intersection of black lines or are there any more data points in between?

All of the data points are those on the graphs. I took about 100 data points today, so these graphs are just some of the data. The rest of it doesn't add much so I haven't tried to graph the rest.

Tomorrow I will cover the reflectors with aluminum foil, take more data. Then spray the aluminum with glossy white paint and take more data. This should add to my understanding of the effectiveness of mylar, aluminum foil and plain white paint for reflectors. I can get all of that on one graph.

One more thing - I took one measurement in my 45 gallon tank, with 110 watts of AHS light kits, at the substrate level, near the front of the tank. It was 90. I need to do a major pruning job on the tank before trying for more readings there, and it is much more difficult to get these readings, for several reasons.

I can't wait to see your results from testing out the aluminum foil and white paint. Thanks a ton for your time and effort! I've been holding out on purchasing mylar as I wasn't sure if I was willing to spend 20 bucks on a big roll of it.

Btw, I might have missed this, but are all these readings in a dry tank or a filled one?

Good luck with all the experiments.

All of the ten gallon tank light fixture readings are out in the open air, with the fixture propped up on a wood stand. For the moment I am interested in what the light fixture can do, so it doesn't do any good to try this is water, and it is much more difficult to do it in water. (There is barely room to get my hand down into the water in a ten gallon tank.)

A min level for most plants is about 25-30.
Max levels are about 450-600.

Full sun = 2000.

Also, if you notice the peak in the middle of the graph when measuring the length of the tank under the bulb.

Since the source (the bulb) is a linear tube, how might this graph change if it was a MH HQI bulb?

Also, consider multiple strike angles here.

If you add 2 bulbs, one on the front and the other on the rear of the tank, how might this influence light intensity?
Measure in the middle, the front and the rear at the same depth.
It should be fairly even now.

Rotate/change the orientation of the probe also as different angles(leaves do not always point directly straight up). Then try it with a single bulb and then with 2 bulbs spaced far apart(like at the front/back of the tank example vs one in the middle or both in the middle).

You can predict the light intensity pretty well vs distance.
Now try patterns from the source of light, angels, reflectance etc and what a real plant leaf does through time.

General physical patterns are fine and do help, but biological patterns are far more interesting and relevant.

Regards,
Tom Barr

Some times you find yourself with egg all over your face, a wet splotch on your trousers, toilet paper hanging behind you, etc. Well, this, for me, is one of those days.

Today I tested two more reflector materials. First I covered the mylar surface with plain aluminum foil, with only moderate care not to wrinkle it. Next, I covered the mylar with white paper and spray painted the paper with glossy white paint. I took PAR readings with both configurations just as I did yesterday, to prove to myself how superior the metalized mylar is - and I have been insisting to all who care to listen that metalized mylar has to be superior. Here are the results: (Ignore my tear drops on the graphs.)


It is obvious how wrong I have been. Aluminum foil, even used with little care to keep the wrinkles out, is much better than the aluminized mylar. But, the real shocker is that plain old paper with a thin coat of glossy white paint is also better than the mylar.

I can either believe the PAR meter, and my eyes, which also gave the same results, or I can insist that my theoretical musings about the superiority of aluminized mylar were correct. Being a retired engineer I will go with the PAR meter results. Back to the drawing board for me!

Yay! My ghetto homemade aluminum foil reflectors are the best! LOL