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AB Aquaspace Cooling System
AB Aquaspace Light
DIY (Do it Yourself) Dual T5 SLR Light Hood
Dual T5 SLR Light Hood Lighting Fixture Hanger
AB Aquaspace Light - Rewiring Project

DMI Metal Halide Pendant

When I first started using Metal Halide lighting I used the pendant style pictured left. I found them to be poor reflectors. I then changed them out to PFO reflectors which worked much better for me. I've since changed out the PFO reflectors for an AB Aquaspace Light Hood.

This unit is made by Design Management Inc.

Metal Halide lights work best when mounted horizontal and perpendicular to the back of the tank, they should not be parallel to the back of the tank. The main reason for a horizontal mount is that metal halides give off lights from the sides of the bulb not the tip of it. If you have the bulb vertical your pointing the dim part of the bulb to the water and using reflectors to bounce the light rays back down to the water. A draw back of a vertical hanging pendant is that the top of them are sealed trapping hot air around the bulb. You want to run the bulb as cool as possible. If the bulb gets to hot it may shorten the life span and change the color spectrum emitted. Considering that metal halide bulbs operate at 700 degrees F or hotter you can see how heat can be an issue.

Since light is emitted from the sides of the bulb and not the tip, a shadow will be casted from the tip of the bulb. (The shadow is actually from light being blocked by some of the internals of the bulb.) If you have a vertical mount, this shadow is casted into your tank. If you have a horizontal mount, but the bulb is pointing parallel to the back of your tank, your still casting the shadow into your tank and pointing the brightest part of the bulb to the narrow sides of your tank. You want your bulbs to be perpendicular to the back of your tank. This aids in casting the shadow out of the tank and into the room. Secondly, you have the brightest part of the bulb parallel to the longest part of the tank - this adds much more light to the tank.

With the bulb mounted horizontally its much simpler to cool the bulb. I use 101 CFM fans mounted in front of each pendant to blow air directly across the bulb. This helps to keep the bulbs cool and removes a lot of heat from the hood of the tank. This is key in keeping your water temperature down. One concern with cooling the bulb is that if you cool the bulb to much you can effect the color temperature and makes the bulb burn with a yellowish cast. After the metal halides have been on all day, the top of my horizontal mount pendants are cool to the touch. Not even warm.

An important tip when mounting metal halide bulbs horizontally is that the "nipple" inside the bulbs needs to be pointing upward to the sky. Not left or right or downward. If you fail to do this the bulb may not ignite at all. Some people report a constant flicker with the bulbs if the don't do this correctly.

Note: Not all metal halide bulbs can be horizontally mounted. Make sure you purchase the correct style of bulb.