What IS Metal Halide?
Metal Halide was produced for mostly commerical use much like Mercury lamps. It fires a charge passing an electric arc through a mixture of gases that ignite producing light. I wont get into the whole technical side of how it works because frankly, its boring and if you really need to know that then there are other resources that can explain it a lot better than i can.
So why should I use Halide instead of Fluorescent lights?
Metal Halide is the closest you can get to natural sunlight. While Fluorescent lights are coming close to doing the same thing, metal halide really is the best type of lighting for a hobbyist that wants to keep a large variety of corals. As present Fluorescent T5 High Outputs are coming close to doing just as well as Metal Halide so that is another option if you dont mind losing the shimmer effect of Halide. In the near future when LED lighting is perfected and the prices come in line with affordability, it could make halide and fluorescent obsolete.
I'm worried about my electric bill and using Metal Halide.
I hear this often and it is a big concern among people setting up a new tank or switch from fluorescent to halide. Keep in mind that if you are running a small reef the increase is minimal and you wont see a huge spike in your electric bill. If you stick with electronic ballasts they are by far more efficient than the old magnetic ballasts.
Can I buy a halide bulb and just wire up a socket for it?
No. Metal Halide requires a ballast to fire. You CANNOT wire it directly into 120v and just fire it up. Generally electronic ballasts are more efficient and run cooler than older magnetic ballasts.
So whats all this SE and DE stuff?
SE= Single Ended bulb. This is the same type of bulb you see in your house with a threaded end that screws into a mogul base. DE= Double Ended bulb. This is a bulb that is connected at both ends in which the current is fired into the bulb. Generally speaking and from a hobbyist point of view DE bulbs are more efficient than SE bulbs since they are fired from both ends and dont lose energy from the threaded connection.
This all sounds great but I hear Halide puts out a lot of heat.
This is true. Halide produces more heat than any other bulb. So much in fact that you cannot put plastic or acrylic as a shield between the bulb and water, it WILL melt or deform it. Halide can increase the temperature of a tank and cause evaporation issues if you're using a large amount of power. You'll see most people hanging it with pendants above the water to reduce the heat and to also not burn the corals by being too close to the water. In most enclosures there are fans to cool the bulb and keep the heat out of the tank but in most cases you'll still see a small increase in temeperature if you're using a lot of halide.
Ok, so i'm ready to buy a bulb but what's this 10k, 14k and 20k stuff?
These are ratings on the PAR which is the Lumens and "color" of the bulb if you will. 10k is the closest emulation too natural sunlight. As the lumens go up in value e.g. 14k you see more of a blue coloration. For more info with pretty pictures check out this link: http://www.cnidarianreef.com/lamps.cfm
Someone told me metal halide puts out radiation. Is this true?
Yes it is true but its in such small amounts that it wont have any effect on you or your tank if you use glass. Most glass has a UV rating of some sort so you dont have to search all over for glass shops that sell it. When I first started i called around like an idiot asking for UV glass and everytime i got the same answer, "All glass has a uv rating". Always use a glass covering over halide and dont stare at the bulb unless you like your eyes burned out of your head.
How long do these halide bulbs last?
Halides should be replaced at least every 8 months. This is a conservative estimate and depending on your light cycle and manufacturer of the bulb, it can last much longer.
Someone told me that i should use halide and actinic supplementation, is this good?
In my opinion, halide + actinic is the best combination to get natural sunlight emulation as well as actinic supplementation for an overall nice look for a tank. Granted, some will argue that you can just use a 14k bulb and call it a day. Really its personal choice but either way they are both great for your tank.
What is the shimmer effect people talk about with halide?
Metal Halide is "Source Point" lighting meaning that the source of light is coming from a single point as opposed to light spread over a large area like fluorescents produce. You can get an example of the shimmer effect by holding a flashlight over your tank pointing at the sand. You will need some surface agitation from a powerhead or pump to get the best effect. The shimmer effect adds a more natural appearance to your tank and is similar to what youd actually see if you were in the ocean looking at corals.
When dealing with Metal Halide bulbs always remember to never touch the bulb with your hands. The natural oils from your finger will contaminate the glass and cause heat to gather in that area and effects the bulb. If you happen to touch it just remember to clean off any finger prints or marks and use a paper towel or tissue provided with the bulb to handle it. This is more of a problem with DE bulbs since they can take some amount of force to put into a DE fixture. As with anything reef related be careful and dont be afraid to ask questions. The learning curve is steep and most people here are more than willing to offer advice and any help they can.
Edited by RBuddha, 29 March 2007 - 06:25 PM.