Light Intensity Variations - some thoughts - Page 4 - Science of Aquatic Lighting

ingg · 05-12-2008, 06:59 PM

Quote:

Originally Posted by guaiac_boy

It's pretty clear that 45W (1/10th) of T5 lighting stretched along my 6' tank wouldn't do it. I doubt 250W of T5 would do it. In fact, I'd guess you'd need pretty close to 450W to get the job done. Where is the error? Didn't we all just accept the "fact" that linear sources are somehow an order of magnitude better? They should be at least 100% better, shouldn't they?

Sorry to throw a wrench, but I run 312 watts of T5's over my 180g, and get results in the same arena with a high light tank. Bright colorations, good growth, from some fairly light demanding species such as Stellata, Hygro "bold", Polygonum Porto Velho....I'd put my growth rates up against a 180g with 3-150w MH, and I think you'd be surprised. I can grow that Stellata from 5" stems to the top of the tank in under a month, for instance.

That is running 8 of the available 12 bulbs. When I introduce a noonburst of 2 hours of all 468 watts in the middle of my normal 9 hour lighting period, virtually every plant in the tank is pearling by the end of the noonburst.

BryceM · 05-13-2008, 11:25 AM

ingg,

There's no denying that T5s are efficient. I'm perfectly willing to believe that 1.73 wpg (312/180) of T5 over a 180g tank acts as a "high-light" setup. If you want to compare growth rates, keep in mind that most pepople who use MH lights only use them for a few hours per day. On my 180g tank the MH's only run for 4 hrs. During the remainder of the 11 hr photoperiod I use 0.86 wpg of T5 (4x39W). This makes it hard to compare apples to apples.

It is still unlcear however, if it is the shape of the light source that is contributing to your success, or simply the fact that T5s are also an inherently effecient method of lighting.

To really answer this, obtaining actual experimental readings would be "illuminating". There are still many variables to control for. Bulb type (mogul vs HQI, regular T5 vs HO vs overdriven) reflector design (Tek, pendants, parabolics), and bulb manufacturer (GE, ADA, etc) all will play into this.

I haven't kept the other plants you mention, but I've not found P. stellatus to be that light-demanding. You can't keep it in a low-light setup, but I've kept it in medium-light tanks without much trouble.

My biggest curiosity with deep tanks is learning how to provide enough light to allow for a nice, dense foreground carpet (of HC, for example) without using so much light that tall stemmies grow insanely fast. I actually recently got rid of my P. stellatus due to its insane growth rate. Trimming three or four times per month gets old pretty quick.

ingg · 05-13-2008, 12:46 PM

Heh, I mow it to the line of my rock, then watch it grow back in for a few weeks. The splitting of stems is getting insane, though, last trim out was over 40 stems - I started with like 8 in January.

I need another local 180g, that runs MH! There is a 215g inside our club, but it is deeper, so tough comparisons again - it is 750 MH, insane light levels and growth.

hoppycalif · 05-13-2008, 07:03 PM

Today I measured some PAR values for a 10 gallon, Perfecto hood light fixture modified to take two 20 watt screw-in CFL bulbs, with good DIY reflectors. See http://www.aquaticplantcentral.com/f...l-light-3.html for details about how I measured this. Here are some graphs of the results:
First - the distribution from one end of the tank to the other at the center of the fixture: (10.25 inches down is about at the substrate)

Then the distribution from front to back:

And, for reference, the distribution from the bulbs to the substrate:

Clearly, the inverse square "rule" almost describes the vertical distribution, at least once you move a small distance from the bulbs.

speakerguy · 05-14-2008, 09:02 AM

Excellent work! Do you have any results for T5 bulbs or linear PCs?

hoppycalif · 05-14-2008, 11:20 AM

Quote:

Originally Posted by speakerguy

Excellent work! Do you have any results for T5 bulbs or linear PCs?

I am posting results as I get them, so no, I only have what I have posted. My 45 gallon tank has two 55 watt AH Supply light kits installed, so I will be taking some measurements with it later.

Today is embarrassing to me. It's like I am walking down the street with egg on my face, my fly unbuttoned, a wet splotch on my pants, toilet paper hanging from my belt, etc. You get the idea I'm sure. For a couple of years or more I have been insisting that the best we can do for reflector material is aluminized mylar, and I have never had any doubts about that. Theoretically it just has to be the best.

So, today I covered my mylar reflector surfaces first with aluminum foil, taking only a little care to avoid wrinkles, then with white paper, which I spray painted with glossy white paint. I repeated yesterdays PAR measurements using these two versions of the reflectors. The embarrassing results are:

It is obvious that I was wrong about the mylar. Aluminum foil, which also gets panned by others, is clearly the superior reflector covering, followed by the glossy white paper, with mylar being the worst. I'm happy to have these results, and I will certainly not forget them, but I really could have done without the embarrassment!

I think the reason why the white paper reflector gives lower PAR readings close to the bulbs is because it gives diffuse reflection, where the shiny materials don't diffuse the light so much. But, at the bottom of the tank, the diffuse reflection is not a problem, and that is where it counts. I'm not sure that is the cause, but it might be.

Bert H · 05-14-2008, 11:41 AM

Very interesting stuff Hoppy.

I have 2 different 50's. One (36 inches wide, AGA tank) is lit via a 96W ahs kit plus a 30W strip, total wattage 126W. The second tank is 30 inches wide (Oceanic), and taller than the first tank. It is lit via 2 ahs 55W retrofits total wattage 110W. It is easy to see that these 110W are brighter than the other's 126W. Whether this is a result of the 30W strip being a cheapie strip or not, I don't know. The second tank's depth is deeper than the first, but I can grow L. aromatica in that second tank, while I can't in the first. I'm sure there is some physics involved in how the 3ft 96W light is distributed vs how the 55W smaller strips distribute it. But that's for others to figure.

newbie314 · 05-14-2008, 01:47 PM

Man, that makes me want to rip out my mylar (but it is shiny on one side and white on the other).

Time to get some Tin foil, yee-ha ..too bad I'm not allowed to put it on my windows during the summer.

BryceM · 05-14-2008, 02:44 PM

Hoppy, great stuff. Any idea what these PAR meters cost? I'd love, love, love to get my hands on one. I'm also dying to see what the effect of various reflectors geometries will be. We all regularly decree with reckless abandon that T5's with TEK reflectors are 9,000 times better than anything else......... Show me the numbers baby!

I'd also like to determine the required PAR for HC maintenance, HC growth, and a lush HC carpet. Once you have those numbers, a particular lighitng design can be easily developed for any size or shape of aquarium.

About being embarrassed...... don't be. Almost all of us here spout off things that we know to be true with no actual data to support our position. Removing personal bias is one the greatest obstacles to true scientific progress.

hoppycalif · 05-14-2008, 04:01 PM

Here is one PAR meter: http://www.apogee-inst.com/qso_spec.htm. Tom's is an Apogee model QMSW-SS with the sensor shown on that page. I don't know what the whole thing costs, but it is around $200 as I recall. More than I want to spend.

One suggestion is that local aquatic plant groups buy one for use by all members. Our group has no treasury at this point, so we couldn't do that. But, it is an instrument of great value when you want to do this kind of measuring, but of no value at all for daily aquarium keeping.