How high to hang Metal Halide Pendants?

Subie

Premium Member
How high from the bottom of the pendant to the water line do you hang your pendants? We have mini Lumen Bright pendants, running 400w Radium bulbs on Galaxy Select-A-Watt ballasts. It's 26" from the top of the water line to the top of the sand bed. Thanks in advance for your suggestions.
 

alton

Active member
8" on my 300DD with 250w MH Lumen Bright Minis. My nephew welded a rack out of 3/4" angle, then painted black.
 

Caravanshaka

New member
Lumen brights are spotlight reflectors, and the recommended height is 16" bulb to water from the manufacturer. It also depends on how big of an area you are trying to light, as the spread will be much different at 10" than 18" for example.
 

Subie

Premium Member
Thanks for the feedback. The pendants are over a 300 gallon tank - 96" long x 24" deep x 30" high.
 

Caravanshaka

New member
I assume you are going with 4 pendants for that length, each lighting a 24x24 square?

I would start at the 16" recommended height and check your par at that height. You should be able to move down and still get enough coverage, but you may find that height to be good for par, and will keep a lot more heat out of the tank being up that high.
 

Subie

Premium Member
We have LED lights (AI) too so that supplements them. Just two for now. I have a third I have not hung up. Any concerns about burning/bleaching corals with a 400w Radium at 16" if the rockwork is 8-10 inches below the water line? We have acros, montis, brains, and zoas. The latter two are at the bottom or near the bottom of the tank, away from the direct line of the Radiums.
 

alton

Active member
I have a PAR reading of 200 in the front left corner on my 300DD with a reading or 250 in the center on the sand. I am not sure where the spot light idea comes from because on my tank that is 72" x 36" they do very well. I added the BML fixtures so during the summer I only have to run my MH's 4 hours a day
 

Subie

Premium Member
I'm going to have to take some measurements tonight then. You're running 250w - I have 400's. My wife thinks that there have been times our corals were burned or reacted strongly to too much light, although from the bottom of the pendant to the waterline is about 12".

Is there any ill effect from running the 400w Radiums at 250w or at the HQI setting?
 

alton

Active member
You might want to try 250w radiums, it will save you the cost of the lamps in electricity cost over a year
 

Subie

Premium Member
Is the light spectrum the same? The bulb cost is within a few cents of each other between the 250w and 400w.
 

alton

Active member
Here is a video from a few years ago before my tank got cluttered with coral and the BML fixtures and you can see how bright the lamps are on the sand

 

Caravanshaka

New member
I have a PAR reading of 200 in the front left corner on my 300DD with a reading or 250 in the center on the sand. I am not sure where the spot light idea comes from because on my tank that is 72" x 36" they do very well. I added the BML fixtures so during the summer I only have to run my MH's 4 hours a day

Is that par reading with or without your BML's on? I assume without, but figured I would double check.

The design of the lumenbright reflector is to focus light, not to spread it. If you look at the angle of each facet, it is designed to reflect the light nearly straight down. What this gives you is more of a spotlight, with massive Par directly under the lamp, but weaker spread compared to other reflectors. Compare the design to say, a lumenarc, which you can easily see was designed more to spread than to focus.

I currently have lumenbright mini's, and I have a par meter and can verify that they absolutely spotlight. I can't cover a 60"x30" footprint at 14" AWL with 2x250w radiums, but I get 900 par directly under the light about 2" below the surface. Move outside of about a 20" square though, and I only have about 100-150 par up there.

This could be the difference in the lumenbright and mini though, as my data is all using the mini. I didn't have room for full lumenbrights in my canopy, but it sounds like that would have been a better choice for my tank.
 

alton

Active member
I took that reading before the BML's, I use SE on my 300DD lumen bright minis. From the lense of the pendant to the bottom front corner is maybe 36"? So that is a lot of room for the light to spread out.
 

alton

Active member
here is a picture of my 65 with a lumen bright mini but DE lamp and you can see the spot light, but on my SE they are not this way? I have been trying to find a used SE to replace this one, because the DE does not put out the PAR levels like the SE. Question do you use the glass lense on yours?
 

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alton

Active member
I love keeping the lense on, protects the lamp and the reflector. My lamps average 16 to 18 months before dropping down 10% below what they where new. I did have one go 24 months before replacing, and one that only lasted 12 months. Meters are priceless!
 
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