BryceM

Um, I hate to be the skeptic here, but this statement is not supported by anything except perhaps a single measurment. You might well be right. Actually, I suspect you are, but until we have good data for comparison with a variety of fixtures, depths, glass vs. acrylic, I don't think it's wise to jump to conclusions just yet.

hoppycalif

I am a retired engineer, not a scientist, so I look at things like this a bit differently perhaps. I know that the light fixture on my 45 gallon tank is good enough to grow every plant I have tried, including a ground cover plant. So, I assume that whatever intensity of light I get with it must be at least moderately high intensity. So, when I measure the intensity in air, that tells me that any fixture that can approximate those measurements will very likely give moderately high light intensity in a water filled tank.

Unlike some measurements, PAR meters give a number that intuitively is meaningless. The number would mean something to me only if I had a history of measuring light intensities (PAR) and could correlate the intensities with something related to plant growth. That isn't likely to ever happen, nor am I likely to do sufficient research to develop a feel for PAR as related to plant growth. So, I am left with just looking at the numbers as being typical for moderately high aquarium lighting.

Now I can better understand why my little screw-in CFL fixture for my 10 gallon tank gives such marginal plant growth. The PAR numbers for that fixture just aren't even close to what I get with the bigger fixture and AHS lights.

If PAR meters were real cheap and a lot of us had one to play with, we could accumulate enough data to arrive at some good conclusions, or if one of us wanted to spend the time and money to do a lot of careful testing, we could also arrive at some good conclusions. For now I think about all we can hope for is some general ideas about the subject.

One such general idea is that plants react to PAR, not to the log of PAR - PAR is not like pH, which is a log function. So a light giving 1/2 of the PAR as another light is half as effective. I didn't even have a feel for that before playing around with this. Another general idea is that plants will grow over a very wide range of PAR - within one aquarium the PAR will be many times higher up near the water surface than at the substrate, but most plants will grow both places, just a lot faster and better at near the surface. This supports the idea that growing carpet plants is the crucial test of lighting, something I was not convinced of before.

The next generation of aquatic plant growers will still have some interesting research they can do.

hoppycalif

Today I measured the light intensity from my 55 watt AHS Bright light kits in my 45 gallon tank light fixture, for different reflector materials, as suggested by Orion2001. To make this easier, I did the measurements with only one bulb of the two installed. First I checked the reflector with no modifications, using the same technique as I used for this fixture before. Next, I covered the AHS reflector with aluminum foil, trying to minimize the wrinkles in it. And, finally, I covered the reflector with white paper, spray painted with glossy white paint. All of the PAR measurements were taken at the fixture centerline, so the light was affected by the reflector, since that bulb was off center above the sensor.

I plotted all of the data, plus the data taken with both bulbs installed, on one graph:


Two obvious conclusions: I get about 50% more light at the center of the tank by using two light kits instead of one. Intuitively I would expect to get about twice as much light. And, aluminum foil and white paint are effective reflector materials, although not as good as the AHS reflectors. I think I may have misread the meter for the aluminum foil test at the closest to the bulb point. (I suspect all three readings for that location should be about the same, since almost all of the light is directly from the bulb with little from reflection.) It looks like aluminum foil is amazingly good as a reflector when you are considering only light at some distance from the reflector, and white paint is a good reflector although, in my opinion, this doesn't support the idea that it is as good as aluminum foil. I suspect a DIY reflector using aluminum foil would be a difficult project to do successfully because the aluminum surface would deteriorate too fast, but I am just speculating on that.

I'm out of ideas now for using the PAR meter to answer questions I have. But, if I think of something else or if anyone has a reasonable suggestion, I will try it.

newbie314

So is the AH reflector with no modifications just shiney aluminium or aluminized mylar?

I have a hunch one doesn't get twice the amount of light from two bulbs is the light of one bulb shiney onto the other.
I my setup (all-glass two bulb hood) it wouldn't surprise me 25% of the light from each bulb is lost to the neighbor. I would think possibly even higher.

The hood would need a good triangular reflect right down the middle of the two so it looks like two single hoods together.
Don't know if this is happening on the AHS or any hoods.

orion2001

Great work Hoppy. Thanks for all the time and effort. Those are interesting results. It looks like aluminum foil is quite a good material for a reflector. I think you hit the nail on its head by talking about comparing your "Air" intensity results with a hood which you know for a fact works well in an aquarium. Comparing light levels in air is then a good idea. Btw, why exactly do you feel that aluminum foil isn't a good long term solution for DIY projects? Just because it is flimsy? Wouldn't it be easy enough to put on a new layer of foil every 5-6 months?

hoppycalif

AH Supply reflectors are made from "Miro 4 enhanced aluminum" from Germany. They are visibly a better quality reflector than anything else I have seen. My fixture has two AHS kits mounted side by side, with the sides of the fixture sloped and covered with mylar for additional reflection. AHS keeps the bulbs quite a long distance from the reflective surface too, so they get maximum effect from the reflectors.

The reason I don't think the aluminum foil will last long is, first, because I have vague memories of being told that by others, and second because shiny aluminum tends to get a hazy layer of aluminum oxide on it with time. It is certainly cheap, so replacing the surface periodically couldn't be expensive.

I haven't tried to glue aluminum foil to anything yet, so I'm not sure how that will work either. I know of no reason why it wouldn't work, but I just haven't tried it. I'm still recovering from the shock of learning my beautiful mylar isn't as good as I thought it was! And, the white paint I have laughed at for so long turns out to be far better than I ever would have predicted.

hoppycalif

Since I last posted on this subject I have been thinking about the results of my "play time" with a PAR meter. One of the things I wanted to check was whether the intensity drop off with distance for a linear source of light differed from that with a "blob" source. Today I downloaded a piece of log log graph paper to further look at this. I plotted my PAR measurements at the centerline of the tank from substrate level up towards the bulbs against distance for both light fixtures I checked, and got this:


What I see in this graph is that once you get a certain distance from the plane of the bulbs, the intensity does drop almost linearly for a linear bulb or set of bulbs, and it drops somewhat close to being an inverse square drop off for "blob" bulbs. But, as you get nearer to the plane of the bulbs, the relationship breaks down, because the light is no longer coming from either a linear source or a discrete blob source, but from multiple directions.

I see this as interesting, but nowhere near conclusive. It just suggests that part of the effectiveness of T5 bulbs is that they are somewhat linear sources. Food for thought only.

zer0zax

Good stuff Hoppy!
IMHO AH reflectors really are worth their salt. Don't feel bad about the low percentages shown in your test (even though they do blow my mind!), take into consideration that you are using the same AH shape for all materials tested

You already know that you are only comparing MIRO4 vs. foil vs. white paint, and AH Supply does claim 162% better reflection, but after looking on the AH website they say 41% comes from the shape and distance of bulbs from the center of the reflector, and 21% comes from MIRO4 vs. Mylar.

Maybe MIRO4 is not really 21% better than Mylar, but IMO it would not be worth the cost to waste Mylar by covering the reflectors in it for testing (or would it? ). At least MIRO4 appears to be 33% better than white paint!!! (at the substrate)

The aluminum foil really my mind though.............

I wholeheartedly agree with you guys that selecting lights should be done based on the substrate plants that will be used. These plants usually require the most light and get the least.

PS: (long rant, I know...) IMHO using foil as a reflector would not be worth it, if you touch it even a little the shape will get skewed. But if you are using a cheap shoplight with white paint.... than why not?!

hoppycalif

The only way I can see using foil is to cement it to something rigid to keep the shape you want. If it isn't perfect that shouldn't be a problem, since the only "perfection" we want is in the percent of the incident light being reflected towards the water. It doesn't matter if the reflected light is not reflected accurately in direction.

I'm intrigued by the white paint. I only used a spray can of bright white paint I had laying around, and didn't take care to get a really good coat of it on the paper I used. I feel sure there are better white paints available, and I know a good job applying it would help some.

treefish

I obviously don't browse these forums often enough because I just discovered this thread today.

Very interesting stuff hoppy.

I admittedly haven't read it all yet. Hopefully I will have some time tonight to thoroughly investigate the data here.

I must say, I'm quite disappointed with your results from the mylar tests; especially considering I am 99.9% certain the mylar you used is from my stock. If you want, I can find the manufacturer information for it. Perhaps conclusions will be different for other mylar types, brands, thickness, etc.

Aluminum foil might be a better choice for your solar cooker as well.

I am also now wondering if the mylar is the reason behind my problems being discussed on another thread. I'm using mylar only as a reflector on 4x24 T5HO. My actual wattage is about 3.3wpg. I assumed I could call it 3wpg safely. Maybe I should have gone with plants that are less light demanding than what I currently have. Certain plants are now dying. This might just be the reason why.