orion2001

Aluminum foil FTW!!

Very interesting stuff. Like guaiac boy mentions, there are soooo many things to play around with. Good luck with all the experimenting!

trag

Well said and a good point.

hoppycalif

Today I set up my 45 gallon tank fixture, using two 55 watt AH Supply Kits, with the GE 9325K bulbs, in a stand similar to how I did the 10 gallon tank fixture:


I took many measurements of light intensity at various locations, including a "map" of the intensity at the substrate level, and the drop off in light at the centerline under the fixture. Here are the results at the centerline, with interpolated results for the ten gallon fixture, with screw-in CFL bulbs plotted on the same chart for comparison.


To better compare the drop off in light intensity with distance, I scaled down the readings for the AHS fixture to match the same PAR reading at 4.75 inches. This shows that the linear PC bulbs do better in maintaining intensity with distance than the screw-ins do. Whether this difference is because the linear bulbs lose intensity with the inverse of distance, while the screw-ins lose intensity with the square of distance, isn't clear to me yet.

BryceM

Hoppy, are your measurements being taken in air?

Brilliant

Did I miss the part where this statement was recanted? Tell Tom to send me the PAR meter...I have Orbit 2x96w and Orbit SLR 2x39w and a deep tank to test it on.

If I understand correctly power compact light is very inefficient because of lost light reflected off water surface. When you make the statement quoted above are you comparing lets say 400w of power compact vs. 200w of T5HO?

hoppycalif

Light is the same without regard for what bulb produced it. So, it doesn't matter if the light you have comes from a MH bulb, a T5 bulb, a linear PC bulb or screw in bulbs. What does matter is the intensity of the light, and the geometry of the light/reflector combination. The reflector just collects more of the light from the bulb and directs it towards the water, and the configuration of the reflector helps keep that redirected light at a sufficiently small angle to the vertical so it isn't reflected to any great degree by the water/air interface. So, what is needed to "punch through the deep water in a deep aquarium" is enough intensity at the surface, with a reflector shaped to direct that light as near vertically as is possible into the water. That can be MH bulbs, or T5 bulbs, because of their superior reflector configuration, or from PC linear bulbs with very well designed reflectors.

That is what I meant by the statement you quoted, and I still believe that to be true.

hoppycalif

Yes, I posted photos of the set up to make that clear. Adding water at this point doesn't help. Eventually it will be interesting to compare the intensity vs distance in air with the same in water. It would also make this a lot easier if I were to use a light detector with a spherical, integrating sensor, instead of the somewhat direction sensitive detector I'm using now.

BryceM

Oh. Hmmm.

There are some factors in an aquarium that might act to mitigate the spread of light as you move away from the source. The sides of the tank will reflect a certain portion of the light back inside. How much depends on the material (glass vs. acrylic) and the specific geometry of the setup.

The air-water interface also comes into play. There is reflection, refraction, and scatter that won't be accounted for during "in-air" tests.

I'm sure Hoppy is aware of all of this, but it's important for everyone to understand exactly how these measurements are being done.

I don't want to sound too skeptical, but I think the data would be quite different in actual aquarium conditions. Is this light meter not submersible?

hoppycalif

Yes, the sensor is submersible, but the effort required to do this in the tank, which is badly overgrown right at the moment, would be excessive. Once I get the aquascape under control, thinned out a great deal, then I can take a few readings to "calibrate" the air readings. I still have no good idea for accurately locating the sensor in the water in three dimensions, which is easy in the air. Then, all of that has to be done reaching under the light fixture and without blocking the light, while reading the meter. If I had three hands and smaller arms it might be easier, but it will be very difficult in any case.

Brilliant

I understand your point about light. The optic and reflector is what makes LED and T5HO work so well but their output is not intense. I think MH is just shear intensity. I have what I would consider decent reflectors and see lots of reflection on my ceiling. Ive seen a 24" deep tank grow extemely well with MH+poor reflector raised high above the tank. Metal halide's intensity seems to be overpowering the physics behind it all regardless of reflector. I think PC mimic idea behind MH and try to do the job with shear intensity. I posted because my PC's are much more intense then my T5HO's which are also proving to be over 100% more efficient. My point is regardless of light and its properties theres the whole wattage and efficiency issue which make any other contenders not worthy in deep water applications.