Gentle Reader,
I see from my 11/10 posting that I'm supposed to discuss MH in a couple of days. I'm really sorry but my mind is slipping fast and I forgot all about it. Now mental health is something that eludes most serious reefers. Just a glimpse through the manic-depressive ranting in any RC forum proves the point. My own meandering posts are a symptom of the paranoia that is so common to this hobby.
Whoops--just saw in my post above and that is MH
LIGHTING I want to talk about.
Never mind.
Ok, the heavy metal of reef tank lighting is Metal Halide lighting. These little babies pack in some serious lighting wallop in a small space. Now metal halide has been around for awhile. Also know as HID (high intensity discharge) lamps; they probably caught on with the type of reefers that grow plants in their basement.
Actually, in a less romantic vain they were developed for film projector lamps and and billboard lighting, amongst other uses.
In the earlier days of reefing MH bulbs where available with higher K values sooner than VHO, probably because their intended use required a whiter light than florescent. If you wanted bright, high K lighting then MH was the way to go. This benefit of a bright light source in a compact area still makes them popular.
Fluorescent lights spread their illumination in a even fashion along the entire length of the tube. Metal halides provide a point source of intense illumination from a single location, similar to the sun. Higher K MH bulbs still appear to be whiter/bluer than VHO bulbs of similar K values, mainly due to limitations in the phospors. Because they are a point source, they produce diffraction bands, glimmer/glitter lines, when the light passes through ripples on the surface of the tank. Probably their only drawback is they get
very hot. I've been informed by people who know more about lighting than I that this is something of an illusion. Just like fluorescent spread the light over a wide area they do the same with the heat they produce. This makes them seem cooler watt for watt although they produce almost the same heat as an MH. I'm also told that the brilliance of MH vs. VHO is apparent because the point source appears brighter than the spread out light pattern of VHO.
All this adds up to the fact that choosing fluorescent over MH is more a matter of preference than actual benefit of one type of illumination over the other.
People with all VHO lighting successfully keep many of the same corals as those with all MH. That is why fence straddlers, like me
, use a mix of both.
Now MH lights come in two main flavors. The first is the single ended or mogul base. These use a screw-in socket like an incandescent lamp. These lamps have a bulb within a bulb design. The inner bulb is the actual light and the outer bulb serves as a heat an UV shield. The other type is the double ended or HQI (high quartz iodide) bulb. These bulbs are more like a fluorescent having connectors at each end and they don't have a outter shield like the single ended.
Very Important!!! MH bulbs emit short wave UV radiation. Looking at an unshielded bulb can cause severe eye damage. Exposure of bare skin to some unshielded bulb for a prolonged period can cause burns.
I don't mean to scare you but I do want you to realize there is some danger involved in using MH, especially the the double ended that don't have a shield. It is important to note also that lime soda glass is an effective barrier to short wavelength UV radiation while high quartz glass is not. Plastic, unless specially coated, is also UV transparent. When using MH always have proper shielding on the hood.
What's that? No, suntan lotion is not a good idea in your tank. It overworks the skimmer
Now, just like a florescent, MH lights need a ballast to run. It serves the same purpose as a florescent ballast, that is, to provide the initial kick to start the bulb and to limit the current flowing to the bulb once it lights. In MH ballasts there are two types of starters. The first is a probe start ballast. Lamps that use this type ballast have a third filament in the lamp that is used to initially start the lamp. The second type is called a pulse start. Here the ballast provides a high energy pulse when first turned on to ignite the lamp then drops down to the operating current after ignition. One needs to make sure that the lamps you buy are the same type your ballast will run. These ballasts also come in magnetic and electronic varieties. The electronic in some cases will run either type of starting systems. They are also more compact than their rather bulky magnetic brethren.
I'm out of time for today but we'll finish up with MH and discuss how we go about mounting our lights next time, which I promise won't take 3 weeks.
