MH Lighting Height

[Christeon]

Just purchased (2) 250w Lumenarc Mini's from Reef Exotics and I'd like to build a new hood to fit them under. My question is how high should the reflector be in relation to the waterline ie. distance from lower lip of the reflector to the top of the water. This is a new tank setup and I'm planning on stocking it with mostly sps and a few lps. Tank depth is going to around 18" after substrate is in. A range would be nice as well as I may make the Hood so I can raise and lower the Halides.

Thanks,
John

 

[Unarce]

Usually a minimum of 6" is recommended, but I'm sure some do it less. There can be some serious crackle and pop if water splashes on a hot bulb or shield.

 

[Christeon]

OOOOOH 8O do i need a shield? Hadn't thought about that really, I guess if any that would get on the shield would be easier to clean than on the reflector and or bulb.

 

[Unarce]

A shield is necessary if you have double-ended bulbs. If not, you're fine. A shield will cut up to 15% of your lights output, so if you have single-end bulbs, you're better without it.

The glass shield will help block the UV output of double-end bulbs.

 

[CG1]

A shield is not only required for double ended - its required as a UV sheild so you don't burn out your corals is you run above 10,000K (but yes, also for double ended period). But I would install a sheild regardless - any water splashes on those puppies and they will explode quicker than anything you have seen.

 

[mgranato]

I would not go any lower tha 8". 250w will easily penetrate 24" depths at 8-12". I run 2x250w 10K single ended on my SPS/clam only tank that's 24" deep and have the bulbs 10" above the surface. If your tank is acrylic, I wouldn't consider anything below 9".

 

[ChrisRD]

A shield is not only required for double ended - its required as a UV sheild so you don't burn out your corals is you run above 10,000K

Not true. A shield is not required for UV protection when running Mogul lamps regardless of color temp.

 

[CG1]

A shield is not only required for double ended - its required as a UV sheild so you don't burn out your corals is you run above 10,000K

Not true. A shield is not required for UV protection when running Mogul lamps regardless of color temp.

Hey Chris - Sorry, but I disagree with you. Single ended lamps do in fact have an outter glass sheild that eliminated "most" of the UV but not all. And when you pump up the Kelvin toward 20,000 you are getting harmful UV even from the single ended. The double ended bulbs have zero built in shield and of course require one.

But the simple fact that they tend to explode is reason enough to desire a cover.

The notion that a single ended bulb emits zero UV radiation is a misconception at best. I work for Osram Sylvania and when I was researching for my lighting I spoke to a couple of our engineers, most of what they said was over my head but I grasped enough.

 

[ChrisRD]

All of the reef lighting we use (including flourescents) emit some UV. The point is that Mogul halides, regardless of color temp, do not emit damaging levels of UV. IMO this is well proven by the fact that reefers have been using these lamps unshielded for many years with no problems.

The notion that 20000K lamps emit more UV is incorrect. In fact, most 20000K lamps emit the majority of their output in the 450nm (blue) range. Many 10000K lamps will actually emit more UV than the bluer lamps. I've attached a spectral chart showing two commonly used lamps in the hobby for comparison (XM 10K and XM 20K).
For more spectral data check out Sanjay's site:
http://www.reeflightinginfo.arvixe.com/

FWIW, I do agree that using a shield with any halide lamp is useful for minimizing the chance of a lamp getting splashed. I also like them from a maintenance standpoint. Personally I find it easier to clean the glass shield rather than having to clean the lamp and reflector.

 

[CG1]

The point is that Mogul halides, regardless of color temp, do not emit damaging levels of UV.

Generally speaking I can agree with this - I am by no means a MH expert, when I was interested in MH's I spoke to my research engineers - each with more PHD's than I have years (and I am an old fart). They expressed what I posted - they did say that the more damaging UV would be blocked by the glass shielding on a mogul lamp. And that the height of the lamp and the depth of the tank would need to be considered prior to saying if a given lamp would give off harmful ranges of UV. So its easier to simply dismiss it and shield it due to the splash effect.

I also may have misunderstood what these guys were saying when it comes to 10,000K --> 20,000K, but I walked away thinking that the 20,000K threw much more UV in a harmful spectrum.

I use double ended HQI's - shielded of course. what I can say is that I started out with three 250 watt 10,000K and later switched out to two 250 watt 15,000k and one 250 watt 20,000K and I love the appearance of my tank.

Oh - but back to Johns post, 6-8 inches and shielded (for splash purposes) :wink:

 

[Christeon]

Thanks for all your answers guys, making it adjustable between 6-10 inches sounds like a winner to me. The lights I bought are single ended 10k bulbs I have my old 4 bulb VHO I'm planning to run just 2 actinics on for color. The tank is a Oceanic glass tank I've had since the 80's.

 

[CG1]

Thanks for all your answers guys, making it adjustable between 6-10 inches sounds like a winner to me. The lights I bought are single ended 10k bulbs I have my old 4 bulb VHO I'm planning to run just 2 actinics on for color. The tank is a Oceanic glass tank I've had since the 80's.

Sounds like a great set up - I like VHO actinics much better than the PC's I am using.