2 of those with the reflectors made for them, in the hanging kit that goes with the lights. DIY hood with acrylic splash guard instead of the light covers that come with them would be optional. Play with it, see what works. These things definitely allow for more freedom. You could also do a retrofit kit of some other kind, this is just an easier version.
In the end, though, wouldn't it be most cost efficient and just plain easier to go with the Hagen? I mean, each strip would be ~$30, so that's $60. + 2x reflector + hanging kit comes about to ~$100. The only difference is that I can play with how wide apart they are and I can play with the acrylic cover to try and weaken the light. My tank is only 12" wide, though, so by suspending any light even a few inches off the water (as it seems I'll probably be doing) I'll get a decent spread. Or am I missing something?
this all has become much more complicated than I had originally thought it would be lol. beginning to remember why I just stuck compact spirals into an incandescent hood.
My first round of calculations is considering that normally the light fixture would be positioned about 1/2inch above the water, since trying to use this equation on a medium other than air is probably just going to add more error. I'm going to say that I want a final wattage of 30W. So:
58.56/30 = (D2/0.5)^2
D2 = 0.699in
Meaning I would need to raise the light a total of 0.199in
That can't be right, right? So I redid the calculations considering distance from the light to the substrate (which introduces the issue that water isn't air, but whatever).
This time, D1 = 11in
So D2 = 15.368in
Meaning I would need to raise the light 4.368in
That seems more reasonable, but tbh that's only due to my preconceived notions that I'm putting a ton of light over the tank so that's going to require so large adjustments on my pat.
My PAR meter testing shows me that it doesn't make any difference whether you have the light X distance from the sensor in air, or X distance from the sensor in water, or any combination of air and water. This is what I would expect, since the light absorption by water is trivial over such short distances. And, that trivial loss due to absorptiion by the water is offset by the slight focusing effect that the air to water interface gives.
So, if the tank is 12 inches deep, with 2 inches of substrate, and the bulb is buried 2 inches up in the fixture, the bulb is 12 inches from the substrate if it sits on top of the tank. Raising it 2 inches reduces the light intensity to (12/14) squared, or 73% of what it was.
Don't assume that T5HO bulbs are 22% brighter than T8 bulbs. They are much brighter than that.
Thanks VaughnH, that makes this much easier to give myself an idea of where I should put it.
About how much brighter do you think T5HO are? 50%? 100%? I think if I put the fixture 4-5inches above the tank I should be in about the right range that I'm looking for (and I'll give me room some light, needed another lamp anyway lol)
I have no good idea how much brighter T5HO bulbs, with their individual highly polished aluminum reflectors, are than T8 bulbs. From the experience of many others who post on forums I can say that a single 4 foot T5HO bulb will grow most plants in a 55 gallon tank - 1 watt per gallon. That leads me to believe that they are at least twice as bright as T8 bulbs, with their typical white painted poor reflectors. I never give much consideration to watts per gallon any more. Instead I look at how far above the substrate the light is mounted. That is what determines the intensity directly below the bulb. Tanks with more front to back depth need more than one bulb to get better uniformity of lighting across the substrate. And, the higher above the substrate the bulb is, the more uniform the light intensity is, both at the substrate and between the water surface and the substrate.
Most of the time, I've found aquarium product reviews are mindlessly good unless the item is decently faulty. I haven't used that fixture my self, but two of those single strips were a prospect until I checked the price.
I think unless you've got a PAR meter, trial and error with height will be the method of choice. It's looking that way for me.