Confusion about MH and chillers!

[KRG]

I've been debating over MH and T5 now for over a month for installation inside of a wall over my 125g. I'm not overly concerned about the intensity of light as this tank doesn't house any sps. Lately I've been leaning towards 3 175w MH-PC pendants because I need plenty of work room inside of the wall and I believe I can mount these much higher than the T5's? I am very confused on the whole chiller thing ! Do chillers always need to be used with MH? Inside the wall I have a bathroom fan that is on it's own thermostat. It will pull air into the wall and is vented to the outside of the house. If I can mount the lights 12" from the surface and since they are the smaller 175 wattage would I still need a chiller? Also, this is an upgrade from 4 65w pcs on a 55g.

 

[Krish]

Chiller's aren't always necessary. It all depends on the temperature of the room and also how much air circulation you have. People get away with just using fans all the time with metal halides, but some tend to lean towards chillers for a bit more peace of mind and temperature control. The only downfall to using a bunch of fans is you may experience a bit more evaporation per day, but every set up is different.

 

[KRG]

Thanks Krish,

That was the answer I was looking for!

 

[dragoneggs]

Krish is right on... it is virtually impossible to 'calculate' the requirement for a chiller. Too many variables to compute. Depending on your specifics you could get away with MH w/o chillers. This is my approach to my new set up. I am going with 2 250w MH with a couple icecap fans and hoping this will suffice. Plan B is to add a chiller but I am hoping for economy sake, I don't have to go there.

 

[dragoneggs]

Of course now with our chill, you might not truly know what you need until July rolls around.

 

[KRG]

Of course now with our chill, you might not truly know what you need until July rolls around.

 

[dragoneggs]

Yeah and I thought I was escaping the cold and went to Carson City on business and it is 10degF here!!!! But at least the sun is shining.

 

[dnjan]

I don't understand the concern about mounting T5's higher above the water. As long as you use decent reflectors, there will be practically no measurable difference in intensity between mounting the lights 2" above the water and 12". It is the light that enters the water that is important, and more of that light comes from the reflectors than directluy from the bulb.

 

[DonW]

I don't understand the concern about mounting T5's higher above the water. As long as you use decent reflectors, there will be practically no measurable difference in intensity between mounting the lights 2" above the water and 12". It is the light that enters the water that is important, and more of that light comes from the reflectors than directluy from the bulb.

I dont know about t-5's but as little as 1" will affect a mh I would assume t-5's are the same.

Don

 

[dnjan]

Not if you have a good reflector. A good reflector will be sending the light down at an angle of incidence of 90-degrees to the water surface. Most of the light will penetrate the water surface, and almost none will be reflected away.

This is also true of the light directly under the bulb (MH or otherwise). But once you move a bit to the side, the angle of incidence decreases and a larger portion of the light is reflected (rathr than penetrating the water surface).

Since most of us are interested in lighting more than just the spot directly under the bulb, we rely on reflectors to efficiently cover a larger area while still having good light penetration. And once you move away from directly under the bulb, more of the light penetrating comes from the reflector, not directly from the bulb. Since the light coming from the reflector comes down perpendicular to the water surface, there is no spreading with distance betwen the reflector and water surface, and therefore no light loss with increased distance between the bulb and water surface.

 

[DonW]

Not if you have a good reflector. A good reflector will be sending the light down at an angle of incidence of 90-degrees to the water surface. Most of the light will penetrate the water surface, and almost none will be reflected away.

This is also true of the light directly under the bulb (MH or otherwise). But once you move a bit to the side, the angle of incidence decreases and a larger portion of the light is reflected (rathr than penetrating the water surface).

Since most of us are interested in lighting more than just the spot directly under the bulb, we rely on reflectors to efficiently cover a larger area while still having good light penetration. And once you move away from directly under the bulb, more of the light penetrating comes from the reflector, not directly from the bulb. Since the light coming from the reflector comes down perpendicular to the water surface, there is no spreading with distance betwen the reflector and water surface, and therefore no light loss with increased distance between the bulb and water surface.

Would you cincider a luminarc a good reflector? My understand is they were one of the best.

Don

 

[dnjan]

I haven't used one, but if they are the reflectors I am thinking of, they are kind of small (area-wise), correct? Their strongest feature is that they capture the light going out the ends, and send it back down to the water. But having a smaller area, they would need to be sending the light down at less than 90-degrees to the water surface in order to cover more tank area.

Reflectors for "long" bulbs are easier to make, as ignoring light loss on the ends of a T5 bulb does not cause much of a total difference. And T-5 reflectors are generally placed side-by-side so that they cover the entire tank. So there is no need for the "less than 90-degree angle of incidence compromise".

On my next tank, I will probably build my own MH reflectors from spectral aluminum sheet. What I am thinking of is full 24" width, true-parabolic, with the distance from the center of the bulb to the bottom of the reflector equal to at least 3 (and preferably four) times the focal length of the reflector. And with semi-parabolic fill-ins on the ends to capture the lost light out the ends. A few years away ...

 

[Herefishyfishy]

Picture of the luminarcs which are awesome!

 

[DonW]

I haven't used one, but if they are the reflectors I am thinking of, they are kind of small (area-wise), correct? Their strongest feature is that they capture the light going out the ends, and send it back down to the water. But having a smaller area, they would need to be sending the light down at less than 90-degrees to the water surface in order to cover more tank area.

Reflectors for "long" bulbs are easier to make, as ignoring light loss on the ends of a T5 bulb does not cause much of a total difference. And T-5 reflectors are generally placed side-by-side so that they cover the entire tank. So there is no need for the "less than 90-degree angle of incidence compromise".

On my next tank, I will probably build my own MH reflectors from spectral aluminum sheet. What I am thinking of is full 24" width, true-parabolic, with the distance from the center of the bulb to the bottom of the reflector equal to at least 3 (and preferably four) times the focal length of the reflector. And with semi-parabolic fill-ins on the ends to capture the lost light out the ends. A few years away ...

Sanjays test show the pfo parallel being the highest.
3062 @ 6" 1599 @ 9" and 829 @ 12" These are with a 10k 400w ushio. Based on this with a 10k 400w bulb, I would be real concerned with t-5's being much higher than a few inches.
Surprisingly the lumin arcs did not do as well as far as par goes anyways.

Don

 

[dnjan]

What was the distance below the water surface that those measurements were made at?

 

[DonW]

What was the distance below the water surface that those measurements were made at?

IIRC no water. I'll have to see if I can find the article. I could only find the notes that I was using for my light lift. Maybe advanced aquarist early 03.

Don

 

[dnjan]

If the measurements were not made below the water surface, then it is very likely that the effects of reflectance and refractance at the water surface were not included in the results. Those effect are not insignificant when you get a little bit away from directly under the bulb.

 

[DonW]

If the measurements were not made below the water surface, then it is very likely that the effects of reflectance and refractance at the water surface were not included in the results. Those effect are not insignificant when you get a little bit away from directly under the bulb.

Yup, so if you put some water in the way that would tell me that height would make an even larger difference. Ive got a elcheapo lux meter and lousy pfo retrofit reflectors and every 1/2 of lift will drop the lux reading lower. So when they hit 24" at night 3 250w halides are nothing more than moonlights.
There should be some pics here somewhere. I dont remember if I posted the lux readings or not but I'll see if I can find them on the home pc.

Don

 

[dragoneggs]

I have a pair of luminarcs... expensive but you get nice coverage in the corners. They are 19.5in square and about 9in high.

 

[dnjan]

Yup, so if you put some water in the way that would tell me that height would make an even larger difference. Ive got a elcheapo lux meter and lousy pfo retrofit reflectors and every 1/2 of lift will drop the lux reading lower. So when they hit 24" at night 3 250w halides are nothing more than moonlights.
There should be some pics here somewhere. I dont remember if I posted the lux readings or not but I'll see if I can find them on the home pc.

Don

Not quite. What I am telling you is that all of the photons you are measuring just above the water surface may not actually penetrate into the water. But the ones hitting the water surface at an angle off incidence of 90 degrees will almost all penetrate.

If you could separate out the photons in your lightmeter readings based on angle of incidence, you would find that those hitting the surface at 90 degrees are affected almost zero by height above the surface (of the light).
The ones hitting at an angle (especially an angle a lot less than 90 degrees) are affected a lot by height.

Af far as your 250MH's being nothing more than moonlights at a distance of 24", I strongly suggest that you not stare at the light bulbs from that distance (at least not when they are on)