att Ninong: metal halide height in canopy

[bongobrian]

I've asked this before, but I'm gonna ask again since I am now in the stages of building my canopy. I'm really at a dilemma with how high I wanna mount the lights off the water. My lights will consist of 2x95w uri vho actnics and 1x 175w 10k hamilton mh. I started building the frame for the canopy at 14" high. I am now wondering if that might be a little TOO high. This design would give the mh about 10" between the bulb and the water, and about 12" between the vhos and the water. I guess I'm just concerned about losing too much intensity by having the bulbs up so high. What do you guys think/recommend? I don't know if there is some type of formula you should follow to determine the height of bulbs. My biggest concern obviously is that the lights provide the best functionality for the reef. Ninong... if you're out there, maybe you can shed some light (heehee) on the subject.

[Ninong]

In choosing the best distance above the surface of the water for any lighting there are several factors that should be considered:

• Is the bulb protected by a UV shield or will it be subject to possible damage from splashing water.
  
• What will be the effect of the lights on the temperature of the water (e.g., would a chiller be required).
  
• If using mixed lighting (e.g., metal halide & fluorescent), should an effort be made to position them so that each is at the optimum distance above the surface.
  
• Will locating the lights too close have any effect on the structure of the aquarium (e.g., directly above a glass or acrylic brace).
  
• What type of reflectors will be used.
  
• What above light spread from the metal halide(s). Is that an issue. Should the bulb be a bit higher to provide adequate light spread.

When you review those issues you will quickly realize that circumstances may cause you to make compromises in your lighting arrangement. You may not be able to position the lights in their ideal position due to other factors.

Ideally you would want the fluorescent lights (NO, VHO, PC) positioned closer to the surface than any metal halides. Most people would recommend 4" or less as the ideal distance, if practical. This is usually difficult to achieve if you are incorporating metal halides in the same setup.

It is obvious that you can position a 175w metal halide bulb closer than a 400w metal halide bulb, all things being equal. A good general estimate might be 5" or more for a 175w metal halide bulb, 6" or more for a 250w metal halide bulb and 7" or more for a 400w metal halide bulb. Notice the "or more" in that statement and don't forget that everything depends on all of the other factors unique to your particular setup: Total tank water volume because of heat issues, height of water column above the sandbed, type of metal halide bulbs used, use of a protective shield or not, etc.

All of that being said, if you are going with a single 175w metal halide and two 3' VHO actinics, I can assume that your tank is probably 36" long and probably less than 65 gallons. In which case, you may need your metal halide bulb to be 9 or 10 inches above the surface to improve the light spread. You would certainly want the VHO lamps closer to the water than that if possible. But maybe that's not possible.

The truth is that anything you come up with will work provided it is reasonable. The corals will adapt anyway provided you use common sense in their placement relative to the light intensity. Certain Acropora spp., as well as T. crocea and T. maxima clams, would do better under a minimum of 250w metal halides but just about anything will do reasonably well if positioned properly under your lighting.

[bongobrian]

Thanks a lot Ninong, that is great info and is very helpful. All of the things you have listed are things I have been taking into consideration. I am coming to the conclusion that the mh should probably be about 10" off the water for a nice wide footprint. If there is a way for me to get the vhos down closer to the water line, would that cause a shadow from the mh? do you think it is reasonable to mount all the bulbs into the top of a 12" canopy?

[Ninong]

You can use brackets to offset the VHO bulbs so that they are lowered from the canopy provided you do not block the metal halide light spread. Again, I have no idea what reflector you are using for your metal halide: A spider-lite type that is mounted perpendicular to the front of the tank or a parallel type that also accomodates VHO tubes???

[bongobrian]

Thanks Ninong.. that is a good idea to use the brackets. I don't have a reflector yet, so I am open to suggestions on which type to use.

[Ninong]

What size is your tank... water volume and dimensions?

[bongobrian]

46 gallon bowfront. 36" wide by about 13" front to back. Not sure how tall it is... it's about 2 feet.

[bongobrian]

and it's about 15" or 16" in the middle where it bows out. It's about 13" at the sides.

[Ninong]

It's 36"L x 15"W x 20"H. That's a difficult size because your front-to-back space is limited, especially on the ends.

[bongobrian]

yeah so I basically have 36" x 13" of usable space for the lights and the reflector.

[Poseidon]

Brian I just added 2 250 watt 10,000K Ab bulbs using Icecap ballasts and Spider light reflectors with the bulbs 7" above the water I get very balanced light distibution over a 6ft tank... I would highly recomend that reflector for your scenario it will fit in the middle of you bow front application placing the bulb perpendicular to the front glass

Mike

[bongobrian]

Thanks Mike, I actually have to place the bulb parallel to the front glass because I will have a vho actinic on both sides of the mh. Will the spider reflector still work if I do this? do you have any pictures of yours? thanks again.

[organicreefer]

placing a bulb parallel to the fron of the tank in a spider light reflector is a mistake.

halide bulbs have very little light coming out of the front and back of the bulb-and the spiderlight is designed to spread the light to the sides ,so in effect youll be sending alot of youre light right through the front and back glass panes.....

i think you should be able to mount it perpendicular and still get some vhos under it.-maybe a shroter flourescent bulb in the front-2 footer or soemthing-so you can push it forward?

[Ninong]

Brian,

The Spider-lite reflector is designed to be mounted perpendicular to the front of the tank but it won't fit into your setup anyway: it is 16"L x 13"W x 5"H.

[organicreefer]

the spider reflectors can be easily trimmed down with a pair of tin snips

[bongobrian]

Is it a bad idea to mount the mh parallel to the glass? it would be difficult to mount it perpendicular with the two vhos. I don't think there would be enough room. There may be a way to do it if I mount the vhos on brackets and mount them closer to the water, then the mh would sit up above the vhos. If it doesn't really make a difference though, I'll probably just stick with mounting it parallel.

[Ninong]

The Spider-lite type reflectors are designed to be mounted perpendicular. There are PFO reflectors that are designed to be mounted parallel but you might want to consider one with two mogul sockets for a 36" tank. The dimensions are 36"L x 12.25"W x 6.5"H and it holds either one or two metal halides plus two 95w VHO actinics. I'm not sure if it will fit or not but it might.

[organicreefer]

the vhos should be mounted below the the halide anyway,just 3-4 inches off the water(id keep the halide at least 8-10").

if you want to go one halide -a spider reflector mounted perpendicular is the way to go-youll definitely be happier in the long run with the better spread.

look at the way a halide bulb is constructed-the "wires" or connections to the arc tube come out of the ends.very little light comes out this way. youll be directing these parts of the bulb to the ends of youre tank-not the most effective method ESPECIALLY on a thin ,long tank utilizing one bulb........

spiderlight is designed taking into account the way in which light is emitted from a hid lamp -and it has to be mounted perpendicular to work as designed.it might be a little more work -but imo system design is half the fun.

[organicreefer]

my diy stand/canopy



heres the link to my diy stand/canopy-scroll down a bit and you can see how i mounted my spiderlight reflectors/vhos.

[bongobrian]

Well I think I could make that work.... I could mount the halide in the middle.. perpendicular to the glass with the spider reflector. I could then drop the vhos down off of some type of bracket, and hopefully the halide with the reflector would be able to fit above the vhos. I probably wouldn't have a reflector then for the vhos, but the uri bulbs have a built in reflector anyway. Do you guys have a link for the spider reflector?