Ok so I have my 200 gallon reef display tank up and under it a 40 gallon refugium that houses my sump and macro and all the other equipment needed to run my tank efficiently. In this tank I keep LPS primarily, softies, button polyps Palyanthoas, mushrooms, ricordea, reef safe fish and some other small SPS corals. Some of the things I added to this build was two overhead 120 watt Aquarium coral reef grow lights 55 x 3 watt blue and white LEDs that are dimmable with 90 degree optics. I am currently working with some folks on determining what LEDs at what wattage and what degree while measuring PAR and keeping LUX in order with tank size and fish and coral requirements.
I currently have my lights sitting on top of my hood which allows me to keep my lights about 7 inches away from my water. One of the things I am trying to do is get as much light from one end of my tank to the other (6 feet approx) well lit and everyone healthy and happy with minimal stress to my livestock.
One thing I am noticing is even though I have the same two lights each one is not lit the same. So unfortunately I have to keep one LED box white lights ramped down a bit to match the other side. I am unsure why this has happened but am making it work due to limited funds I set aside for this project.
So. here is my dilemma. I am noting die off of coralline algae (which I love it is various shades of pink and green) on the upper reaches of my tank rim which tells me that light is not reaching those areas. I am also noticing that the ends of each side of the tank are the darker areas of my tank.
now while I understand that I could easily lift my lights higher off the tank and suspend them from the ceiling to create a wider reach (degree) and that would solve my problem it is a high ceiling and I dont wish to put holes in them to hang these lights above my tank. So the next thing I thought about was what if I add reflectors of some sort under the hood and perhaps keep more light in my tank and perhaps lighten the ends of the tank even more?
So I thought how would I do that? As we all know in this hobby the internet can be a great resource but not always a reliable source. So I did a little investigation. What options would a person have to reflect any amount of light back to its source? Well there is reflectors you can buy and adhere to the hood of my tank lid. Too expensive and the cleanup just was something I didnt want. So then I thought what about Tin foil? Chrome Tape? Mirrors? Mylar? That was a pretty inexpensive thought and then I saw how some lights reflectors were coated in white epoxy. So I did a little investigation as to which would be more reflective and what did it actually reflect? I really liked the white paint idea. it reflects light without it going through it like Mylar and you lose alot of the beneficial light needed for a reef tank.. Now for the record the hood lid of my tank where my lights sit is black so Im thinking anything is better than nothing.
My thoughts were while I had all these great ideas which was better at reflecting the most of the light I needed or rather my reef needed to make it worth my while.
So here are some results in LUX....
Distance No refl. White Alum. Triton reflector ($$)
in inches paper foil
29 100 180 120 350
22 180 290 210 550
16 290 460 350 960
11 460 760 570 1560
A photographic photometer is not a very precise device. By repeating each
measurement several times, each one with a different focusing ring
adjustment and/or slightly changing the framing of the target, I estimated
that I can tell apart light levels that differ by 1/4 of f/stop. That
translates to about 18% precision, or equivalently a plus-or-minus error
of approximately +-10%.
Even with that modest precision, the differences among the different
reflectors are large enough to stand out clearly. There are a couple of
interesting effects that we can see if we plot the data as a function of
the inverse distance.
The important point I want to emphasize here is the large gain provided by
the expensive reflector. It more than triples the light, as compared with
a no-reflector situation. A white diffusive reflector does provide a
more modest gain, of the order of 1.6-1.8, not bad if we consider its
cost (nothing). The aluminum foil reflector, on the other hand, is barely
worth the trouble. Aluminum foil would possibly make a good reflector only if
it can be laid out smoothly as a polished mirror. The wrinkles on the foil
turn it out effectively into a diffusive reflector, and a bad one...
This suggests me that the use of reflective flexible materials such as
Mylar and similar ones does not provide a significant gain above what one
can get with a simple white paint. They can be even worse than the white
reflector, as in my test. The reason is the difference between specular
and diffusive reflection. Unless the reflective material can be laid out
with a smoothness comparable with a true mirror, it will tend to act as
a diffusive reflector. And will most likely perform below the "perfect"
diffusive reflector, a white matte surface. Stretching this reasoning a
little, *any* shininess in the reflective material is prone to *decrease*
the reflector effectiveness, unless it is *perfectly* smooth as a mirror.
That is, unless you can see your image clearly reflected when looking into
it.
An important point to consider though, is that with this particular
Triton reflector, probably the large gain only applies when the reflector
is used with a single tube. The dimensions of this reflector and its matched
lamp holders suggest that it is optically optimized to work with a single
T12 bulb. Nevertheless, the manufacturer claims that the reflector can
be used with two or even three tubes. With two tubes, the gain would not be
that impressive. The tubes cannot be placed precisely at the parabola focus
anymore, and that completely breaks down the reflector optical properties.
Also, the amount of self-shading and restrike gets large with two T12 tubes.
With three tubes, just forget it. The effect will probably be to *decrease*
the light as compared with a no-reflector situation, due to almost complete
self-shading and tube overheat.
Of course, these are "dry" measurements and in a real situation with water,
things can be quite different. However, my goal here wasn't to get absolute
values of light level at the inside of a water-filled tank, but to get a
*relative* comparison. Most likely, the relative performance of these
reflectors will still hold when used over a water-filled tank. I would
expect a slight decrease in performance of the diffusive reflectors as
compared with the Triton, due to large angle of incidence effects at the
water surface.
So in the end I decided to paint the underside of my hood and wait for it to dry and test it out. I do understand that over time it might yellow out and become less effective but for now I will see how it goes and if I need to paint again who knows maybe Ill just do that or make a project out of placing my LEDs a little higher no more than another 6 inches above my tank for wider output (degree).
PLEASE NOTE: That this article in no way suggests what lights should be used or what is better that is another article I hope to put together in collaboration with some experts on that subject and then we can get into PAR and at what levels in a tank you produce what amount of PAR and what the items in your tank require PAR to be in order to thrive and grow.
Results of painting underside of hood white were a significant difference. Even the fish noticed and kept looking up wondering what the difference was! I have since turned the whites down a little bit to acclimate them up to the intensity over a two week period. But where I noticed the biggest difference was on each end of the tank. It is brighter and I have less dark spots. Which was my goal.
Thank you all for reading!
