Tom-

FWIW I owned a "Lux meter" back in the early 90's to record levels at different depths in my reef aquaria, but I dont qualify as a hobbyist. At that time i was a retail saltwater store owner.

So after digesting 70% of this technical thread data, and feeling very sleepy i have a really EZ question for you. Do you prefer fluorescent (regardless of type) or metal halide, or both in combination. Dont over think this question as it pertains to different planted aquaria etc. just looking for a general answer ( ie your opinion.)

Im a dinosaur saltwater guy, and a plant tank newbie (in progress) Thanks for the forum, its exactly what i was looking for.

OK, now I am thoroughly confused. After reading up on Mylar on Wikipedia (yes, I know it isn't the most reliable place for info) :
PET film (biaxially oriented - Wikipedia, the free encyclopedia)

It seems that Mylar as we know it is basically a metallized version of this PET polyester film. The mylar that we use is actually aluminum metal in PET!! Now this makes it extremely hard for me to figure out how Mylar isn't giving better/equivalent results to aluminum foil. Given the processes used to metallize Mylar, I'd assume you have very low surface roughness (which explains why it looks so much like a mirror). Also considering

The wiki on Aluminum states:

"Aluminium is one of the few metals that retain full silvery reflectance in finely powdered form, making it an important component of silver paints. Aluminium mirror finish has the highest reflectance of any metal in the 200–400 nm (UV) and the 3000–10000 nm (far IR) regions, while in the 400–700 nm visible range it is slightly outdone by tin and silver and in the 700–3000 (near IR) by silver, gold, and copper."

Hoppy, this is my theory. Let me know what you think of it. It could be, that in the case of your Spiral CFLs, your reflector geometry isn't optimal for something as highly reflective (next to zero diffuse reflections) as mylar leading to significantly higher light losses due to restrike. On the other hand, Aluminum foil, though not as reflective as Mylar, causes more diffuse reflections which basically lower this restrike as some of the light that would be reflected straight back into the bulb is now being scattered at different angles, bouncing around and in general providing better illumination. This would also explain why something like the white paint on paper behaved quite well since it is entirely diffuse in its reflection of light...again lowering restrike effects.

Something I had thought about a while back but never fleshed out in my head is the following idea:

For non optimal reflector geometries, there is a good chance that a completely diffuse reflector such as white paint or a partially diffuse reflector such as aluminum foil will provide better illumination than a perfect reflector like Mylar since the non optimal reflector design coupled with the perfectly reflecting Mylar surface will cause a significantly larger amount of restrike and thus, losses. On the other hand, diffuse reflectors in such a situation would cause some of this light that is being forced to "Restrike" due to the non-optimal reflector design in the case of Mylar to be scattered in other directions which wouldn't experience "re-strike". This effect would be even more pronounced in the case of Spiral CFLs since they have a geometry which lends itself to a lot of restrike. In addition it is next to impossible to design an "Ideal reflector" for Spiral CFLs. In this case, diffuse reflectors are probably the best materials to use.

I don't know if this is clear in words. I could draw a diagram to explain my idea.

I would postulate that for a T5 tube (restrike being less of an issue) and an optimally shaped reflector (see pic below), Mylar should still be more effective than aluminum foil or white paint (As Tony Gomez in the site linked below seems to believe).



This picture is from Aquarium Plants - Info Pages , interestingly the author claims that white paint is much better than aluminum, and hints that mylar would be the best.

I'd love to hear what people think about this idea.

I tried to put this reasoning into some sort of math. This is what I came up with:

X is the fraction of light emitted by bulb that restrikes the bulb for a perfect mirror material(mylar) used for a suboptimal reflector geometry.

Fraction of light emerging out of fixture for Mylar = 1-X

Now consider a diffuse reflector.

If light is incident on a diffuse surface (lets assume perfectly diffuse...meaning equal probability of reflection in all directions in a hemisphere from the surface) then a fraction of the total light will actually restrike and be reflected back into the bulb. IF we call this fraction Y, Y can be expressed as the ratio of the angle subtended by the bulb at the point on the reflector to the total angles it could be reflected at (ie 180 degrees for a hemisphere). Now this ratio Y would change depending on which point of the reflector you are at. Right above the bulb, at the point on the reflector closest to the bulb, this ratio would be the greatest (it is clear in the picture in my previous post), whereas at a point on the left or right portions of the reflector, this fraction Y, is lower. A good guess at what the mean value of Y should be, if you integrate across the whole surface might be Y=0.2-0.3. Lets assume Y=0.25.

This implies that in the case of a perfectly diffuse material you would expect 1-Y=0.75 of the total light being output by the bulb (in the upwards direction) to be available. So roughly you would get around 175% of the light as compared to if you had a perfectly black reflector.

Now if you have a perfect reflector geometry, X can be extremely small for the perfect mirror material. However the efficiency for a perfectly diffusive surface will not improve much at all since the diffuse nature will cause light to scatter in all directions. An interesting corollary is that perfectly diffuse reflectors will be very insensitive to the geometry of the reflector in terms of how efficient they are. The variability in performance of diffuse reflectors for a whole host of geometries should be pretty low.


It is very easy to see that in the case of a perfect mirror surface like Mylar, for a spiral CFL and non optimal reflector geometry, the fraction X could easily exceed this value of 0.25, and in this case a diffuse reflector would be a better option as compared to a perfectly reflecting material.

Hard to say.
They are very different for a number of reasons to me personally.
Aesthetics are vastly different.

I like mixing color temps, always have going way back.
This always seemed to give me a nice color I liked.
I tend to like warmer color temps than most these days.

For bring out reds, FL's, say the GE 9235K's are very hard to beat or the triton bulbs(but they only make a straight pin 21" bulb or the T12/T8 sizes), I also have a nice mix with 8800K and 5000K CSL PC bulbs, but no more(no longer made).

MH's always washed out many colors but the pearl intensity and the shimmer, greens, always seemed really pretty.

One is point source and displays a different pattern under water, whereas the FL's will do something different, point source vs the linear line of light.

Mixing the trade offs of each with each other is what I do for myself and clients.
So I prefer both.

I can run my tanks at low light, about 100 micmols down to 30-40 with the PC's, or go to the high light ranges with PC+MH and have 80 at the lower ranges/edges, up to 600 in the hot spots.

Regards,
Tom Barr

I suggested mylar in the past as well.

It may depend on the shape of the foil or mylar.
Foil can be bent and messed with over time, mylar stays fairly stable and doesn't crinkle(which can help or hurt you with PAR).

I made curved arcs like the reflectors using mylar.
It's been awhile since I've used it.

Regards,
Tom Barr

Orion: First a bit of nit picking: fluorescent tubes, whether T5, T8 or T12, all emit light from the inside surface of the tube, not its centerline. The centerline of the bulb contains the mercury arc which emits UV, which strikes phosphors on the inner surface of the bulb, which absorb the UV and re-radiate the energy as visible light. So, Tony's chart you showed isn't at all accurate, and there is no optimal reflector for a fluorescent bulb.

Yes, I understand your theory about diffuse or imperfect reflection vs near perfect reflection. You may be correct, but I don't know any way that I have available to verify that. One could do an experiment with a light source that approaches being a point source, with a simple flat reflector, but the sensor would have to be very small for the experiment to work. (I think.)

The mylar I am using is, I think, aluminized on both the front and back surfaces. Neither surface is 100% metalized, but the combination comes close. (Some light goes through the metalizing through the gaps.) That is one source of inefficiency. Another source is the anti-oxidation coating on the aluminum coating, and I don't know what that is or how thick it is.

Mylar looks so "perfect" only because it gives a very nearly true reflection, so it works reasonably well as a mirror for shaving, for example. But, our eyes are extremely capable of using a wide variation in light intensity and ignoring the variatiions. So, if only 80% of the incident light is reflected the mirror effect will still seem to be perfect.

Aluminum foil, not having nearly as perfect a surface, looks like a poor reflector - it gives a distorted image. But, our eyes concentrate on that aspect and ignore the higher percentage of incident light being reflected. That is my opinion.

White paint gives pure diffuse reflection, but appears blindingly white only because such a high percentage of incident light is reflected. That reflected light is reflected at small angles off of perfect reflection, making it useless as a mirror, but the small angles are not great enough ot greatly reduce the total amount of light being usefully reflected. Again, this is my opinion.

Others have been posting that mylar isn't really very good as a reflector, and that white paint is very good. I couldn't accept that since it was so counter intuitive. Those "others" also have said that aluminum foil isn't a good reflector. I intuitively accepted that. What I think we have here is a failure of intuition.

Below is a plot of my data yesterday for my 45 gallon tank fixture with AHS light kits, measured along the length of the fixture at the depth of the top of the substrate. I added the data for the 10 gallon fixture with the screw-in CFL bulbs for comparison.


I think the drop off in intensity results because as you move towards the ends of the fixture the light contribution from the opposite end drops off rapidly, and there is less contribution from the shorter end in the opposite direction.

It should be clear that there is no one number that characterizes the light from a light fixture, no matter what bulbs or reflectors are used. So, we might as well just use wattage and bulb/reflector type as our descriptive "number" for such fixtures. i.e. 110 watts of AHS Bright Light kits with GE 9325K bulbs.

Today, after extensive thinning of my plants, I managed to get a reading with the PAR meter, at the substrate, about 8" to the left of the centerline and at about the centerline from front to back. The reading was 50 - 80, depending on whether I moved an inch one way or another. This is reasonably close to the value I measured in air. I still have no way to accurately position the sensor way down in the water like that, and the remaining plants can shade the sensor enough to drop it to a 20 reading with just a small movement in either direction. Clearly one would need a tank without plants to measure the actual light intensity unaffected by the plants. I see no way to determine the distribution of intensity as I did in air.

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. 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. 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.)

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

Same tank and reflectors - different bulb types? Maybe that would be difficult without removing the fixture though....but you could do T8s and T12s on the same fixture if you had two bulbs of the same size.