DIY Guide to Metal Halide Lighting Systems

Metal Halide (MH) lighting is often intimidating choice for the beginning reef aquarist and DIY enthusiasts. This article will provide the basic background of MH lighting systems in an effort to provide an understanding of the base vocabulary and the hardware components.

The basic components of a MH lighting systems are as follows:

  1. Lamp
  2. Ballast
  3. Socket
  4. Brackets
  5. Fans
  6. Reflectors
  7. Wires
  8. Hood/Enclosure

 

MH Lamps

MH lamps fall into the category of HID (High Intensity Discharge) lamps. This group includes the mercury vapor, high-pressure sodium and metal halide lamps. The basic construction of the lamp is two envelopes - an inner envelope (arc tube) which contains the arc, and the outer envelope (called bulb) which filters out the UV and shields the inner arc tube. The inner arc tube contains the electrodes and various metal halides, along with the mercury and inert gas. The typical halides used are some combination of sodium, thallium, indium, scandium, and dysprosium iodides. These iodides control the spectral power distribution of the lamp and provide the color balance by combining the spectra of the various iodides used.

As a DIY aquarist, we are more concerned with the characteristics that impact the selection of the lamp and the associated hardware. MH lamps come in a wide variety of configurations differentiated by the wattage, color temperature of the lamp, mounting base, shape of the bulb, electrical characteristics, operating positions, and manufacturers.

When working with a DIY MH lighting system it is best to start with the selection of the lamp, and select the other components based on it.

The first choice to be made is the wattage of the MH lamp to be used. Typical MH lamps are available in 70W, 100W, 150W, 175W, 250W, 400W and 1000W. The ones most commonly used for home aquaria are the 175W, 250W, and 400W configurations. The choice of the wattage of the lamp to be used will depend on several factors related to the type of corals to be kept, depth of aquarium, electricity costs, etc. which are outside the scope of this article.

Once the wattage of the lamp is decided, the aquarist is now faced with the choice of the color temperature of the lamp. Lamps below 5000K are not usually recommended for use in reef aquaria. The commonly used lamps have color temperature designated as 5500K, 6500K, 10,000K, and 20,000K, with the bulbs appearing bluer as the color temperature increases. Table 1, shows a list of the commonly available lamps frequently used in the hobby.

MH lamps are sensitive to the manner in which they are mounted, due to the sensitivity of the shape of the arc in the arc tube. Lamps are designed to operate best in a certain orientation. Universal lamps can be operated in any position, however there is a reduction in life and light output when used in off-vertical position. For best performance, if the position of lamp operation is known in advance, the position-oriented bulbs are best. Various codes are used to designate the burning position (eg. U = universal, BH = base horizonal, BUD = Base up/down (vertical) etc.).

After the specific lamp is selected, the next step is to check the mounting base of the lamp. The lamps most commonly used in the hobby are single ended lamps, with a screw type-mounting base. The size of the base and the threads is also described by a code, although names are more commonly used. For example, Base - E39 is commonly called a Mogul base.

ANSI Designation of MH Lamps

To provide a common system for identifying lamps, and to allow lamps to be cross referenced with different manufactures and selection of the proper ballast, the ANSI (American National Standards Institute) system is used to designate the lamps. Designation of MH lamps that follow the ANSI system start with M followed by a number, which identifies the electrical characteristic of the lamp and consequently the ballast. After the number are two letters that identify the bulb size, shape, finish, etc. excluding color. After this section, the individual manufacturer may add at their discretion any additional numbers or letters which they desire to indicate information not covered by the standard section of the designation, such as lamp wattage or color. For the purpose of ballast selection only the letter M and the number that follows are important. For example a lamp with the ANSI designation M59-PJ-400, will operate with any ballast designated for M59 lamps.

Another characteristic of HID lamps that a DIYer should be aware of is that the HID lamps take several minutes to warm up (ranging from 3-5 min). After any interruption of power, a lamp that is hot will not start immediately, and must cool sufficiently before restarting. This time delay is called the restriking time and may take anywhere from 10-20 min for MH lamps.

 

 

Table 1. Commonly used MH lamps in Reef Hobby

Lamp Wattage

Base

ANSI

Color Temp

Manufacturer

Manufacturer Designation (if availabe)

150

Medium

M102

6500K

Iwasaki

MT150D

175

Mogul

M57

5200K

Venture

MH 175/U/5K

6500K

Coralife

 

10,000K

Aqualine Buschke

 

20,000K

Coralife

 

20,000K

(german) ??

 

10,000K

Coralife

 

250

Mogul

M 58

5200K

Venture

MH 250/U/5K

H 37*

6500K

Iwasaki

MT 250DL

M58

10,000K

Aqualine Buschke

 
 

20,000K

Osram

HQI T 400W Blue

400

Mogul

M59

5200K

Venture

MH 400/U/5K

H 33*

6500K

Iwaski

MT 400DL/BUD

MT 400DL/BH

M59

10,000K

Aqualine Buschke

 

10,000K

GE (Hungary)

KRC400/T/H/960

20,000K

Radium

HRI-T 400W Blue

20,000K

Osram

HQI T 400W Blue

20,000K

Coralife

 

* The Iwaski lamps are designated as replacement MV lamps hence require H33 and H37 ballast. However hobbyist have been using them without apparent problems with a ballast rated for both M59 and H33 (or M58 and H37).

Most of these lamps (other than the 5500K) are specialty lamps and often difficult to find and get a reasonable price through a local electrical supply. The best sources are the aquarium mail order businesses. Two good sources (I buy my lamps from these sources) are Marine Depot (www.marinedepot.com) and Reefers (www.acropora.com).

 

Ballast

The ballast provides the proper starting voltage, operating voltage and current to the lamp to initiate and sustain the arc. HID lamps have a negative resistance characteristic, which causes them to draw an increasing amount of current, hence need a current limiting device. The ballast provides these functions.

Once the lamp is selected the next step it to select the ballast that will be used to drive the lamp. When putting together a DIY MH lighting system it is very important that the ballasts be matched to the lamp in use. An easy way to match the ballast to the lamp is through the use of the ANSI designation. For example, when using a lamp designated M-57, look for the ballast with the same designation. For lamps without ANSI designation, it is best to call the lamp manufacturer and get a recommendation on the ballast to be used.

Most ballasts (except the electronic ballasts) used for Metal Halide lighting are of the CWA (constant wattage autotransformer) type. This is lead circuit ballast, and consists of a high reactance autotransformer (core-coil) with a capacitor in series with the lamp.

Any ballast rated for the lamp will function properly, but may come in different configurations, each with its pros and cons, differences in prices and amount of DIY work required. There are several manufactures of ballasts that will operate the same lamps, and often the exact brand is not important. The ballasts can be cross-referenced with another company's ballasts if a specific brand is desired.

(1) Core & Coil Ballasts

The most commonly used ballast is the core and coil type, which basically consists of a transformer (core and coil) and a capacitor. The core-coil ballasts are sold as kits, which include the transformer, capacitor and the mounting rails. From the DIY perspective, these ballasts are the cheapest kind since they are mass-produced for commercial MH lighting purposes. Unfortunately these are designed to fit in the standard housing of the commercial lighting fixtures. What this means to the DIYer is that a box will have to be found or fabricated to house the ballast. Running these ballasts exposed is not a good idea.

Example models of these ballasts are:

Manufacturer

Watts

Part/Catalog Number

Advance

175

71A5570-001

250

71A5770-001

400

71A6071-001

Magnetek

175

1130-11R

250

1130-12R

400

1130-13R

Using these part numbers your local electrical supply store can either obtain these ballasts or find the equivalent ballasts from other companies that will work. Some good sources for core-coil ballasts are the hyrdoponic gradening stores. Two very good and cheap sources that I have found on the Internet are, Enerficient Lighting Equipment Co. (http://www.enerficient.com/magnetic.htm) and PFO Lighting Inc. (http://www.aone.com/~pfolight/ballast.html).

(2) F-Can

The F-can ballast is very similar in appearance to the fluorescent ballast, and these are potted in FL type cans and utilize asphalt based insulating materials. The F-can ballasts may also have thermal protectors, which cut off power to the ballast if overheating takes place. These ballasts are also called tar ballasts due to black asphalt based material used. Since these ballasts are already enclosed in a flouroscent type case, they are much easier to work with, and can be mounted anywhere easily. Since these ballasts are designed for indoor use, they tend to have less "ballast hum". These ballasts are more expensive when compared to the core-coil ballast, but the additional cost may offset the cost of the box and additional DIY work needed for the core-coil ballasts.

 

Example models of these ballasts are:

Manufacturer

Watts

Part/Catalog Number

Advance

175

72C5581-N-P

250

72C5782-N-P

400

72C6082-N-P

Magnetek

175

1110-245SC-TC

250

1110-246C-TC

400

1110-247SC-TC

 

 

Ballasts for MH lamps are often available in a Multi Tap configuration. What this means is that the same ballast can be used for different input voltages (eg. 120/208/240/277), by selecting the right combination of wires leading into the transformer coil. The combination of wires to be used for a specified voltage will be indicated in the wiring diagram and often labeled on the wires too.

 

(3) Electronic Ballast

Recently, electronic ballasts based on digital electronics have become available for Metal Halide lamps (manufactured by ICECAP Industries (www.icecapinc.com) for 175W and 250W bulbs). These ballasts have been shown to be more efficient, than the standard MH ballasts.

(http://www.aquariumfrontiers.com/1998/april/product/default.asp). One problem with the electronic ballasts is that they often have to be tuned to the specific bulb or classes of lamps. This may be a problem if you want to change from say a US made lamp to a German or Japanese lamp, since it requires sending the ballast back to the manufacturer for re-tuning.

Socket

The socket used for mounting the bulb must have threads and size similar to the bulbs being used. The sockets for the 175W, 250W and 400W lamps have a E39 base and are mounted in sockets called mogul sockets. The European lamps have a E40 base, which will also work with the mogul socket (there may be a occasional problem due to the slight difference in size of the European lamp and the lamp not making proper contact). The sockets are made of porcelain and have terminals to which the wires from the ballast will need to be connected. In addition the socket has mounting screws which are used along with nuts to mount the socket to the bracket. Mogul sockets can be easily obtained from your local electrical supplies store. One manufacturer of these sockets is Leviton (Cat. No 8781) (www.leviton.com).

 

 

Bracket

The socket needs to be mounted into a bracket, to hold it firmly in place. A simple bracket can be fabricated by bending a strip of aluminum into an L, and drilling holes for attaching it to the hood, and attaching the socket to it.

 

Wires/ Wiring

Wires used in electrical circuits are often of two types, stranded or solid, and are rated by size, current capacity and temperature handling capability of the outer plastic sheath. Stranded wire is flexible, and much more resistant to breaking.

The wire size is indicated by the gauge of wire. It describes diameter (smaller the gauge the thicker the wire) and is directly related to the maximum current that the wire can handle. For our purposes, and for lengths under 25, we can run a lamp up to 1000W on 18 gauge wires. This takes into consideration a line voltage of 120VAC and a moderate safety factor.

The outer insulating jacket of a cable is rated for a specific voltage. Most insulation is rated up to 600 volts, which is fine for our purposes. The outer jacket is also rated with a letter designation. S denotes a high quality, 2-conductor cable with an outer jacket of high-quality rubber. SO or SJO denotes the same, with an oil-resistant jacket of neoprene or similar material. In the environment we use our lighting, these are a good choice. If using single-conductor cable, THWN refers to a water-resistant thermoplastic insulator, and is the best choice.

When wiring ballasts remotely from the lamps, it is often convenient to use a connector of some sort so that the two components can be disconnected. A simple solution is the use of normal household extension cords, cut in two, with one end wired to the ballast, and the other to the lamps. The female connector should be connected to the ballast, and the male to the lamp, so that an energized plug could not come into contact with your hand. Other good connectors such as Hubbell twist-lock style connectors provide a locked connection, and are different from most household connectors.

The wiring diagrams for connecting the ballast to the lamp are usually printed on the ballast cover. Always use a three-pronged plug for connecting the ballast to the outlet, and make sure the wires are properly grounded. Most circuits require that the outer case of the ballast be grounded.

When working with electricity, please exercise caution and seek the advice of a qualified electrician if you are unsure of what you are doing.

 

Fans

Heat dissipation is an important aspect of the hood and enclosure design. For the purpose of heat dissipation, fans are mounted in the hood/enclosure to increase the air flow through it and remove heat by convection. Small fans 3-4" size are a good way to more the air through.

Fans are rated by their size (fan diameter), amount of air moved (cfm), operating noise level in decibels (dB), and the type of input power. For use in the hood it is best to select fans which require the normal household voltage, so you dont need any auxiliary power supply. When selecting fans, try to select ones that are provide a good airflow at lower decibels, especially if noise is concern. A fan with about 100cfm airflow with a noise rating in 40-50 dB range would be adequate for most lighting enclosures.

A good source of cheap fans is through surplus stores. These stores sell used/salvaged fans at a very reasonable price, ranging from about $6-$10. One such source of surplus equipment that I have frequently used is Marlin P. Jones & Assoc. Inc (1-800-432-9937).

Fans can be mounted such that they are either blowing air into the hood or blowing air out of the hood. Depending on the size of the hood 2 or more fans may be used. A disadvantage with using fans such that they are pulling air out of the hood is that they corrode very quickly due the hot, salty humid air that passes through them. In my hoods I use two fans, one blowing air in and the other blowing air out, creating a flow through the hood. When blowing air into the hood, make sure that there is a way for the air to escape easily.

Reflectors/Reflecting Surfaces

To maximize utilization of the light output by the lamps, the use of reflectors or reflecting surfaces is highly recommended. One approach is to use commercially available reflectors that are designed to provide a good spread and intensity of the light. One such reflector is the recently available Spider Light (www.digitaloceans.com). Before using such a reflector you might want to check to see if it will fit in the hood/enclosure you are planning to build. Also, make sure that it will leave enough room for any additional fluorescent lamps you might intend to add.

The other approach is to line the inside of the hood with a reflecting surface. Various types of reflections can be produced depending on the surface used for reflection. If a surface is polished it creates a specular reflection. Examples of specular reflectors are smooth and polished metal and aluminized or silvered smooth glass. If a reflecting surface is not smooth - that is, corrugated, etched or hammered it creates a spread reflection. If the reflecting surface has a rough surface or composed of minute crystals or pigment particles it produces a diffuse reflection. Flat paint and other matte finishes produce diffuse reflection. Most common materials used in reflectors are compound reflectors and exhibit all three reflection types to varying degrees. Reflectance of 70-90% can easily be achieved with the various materials discussed below. The shape of the reflector can also have a large impact on the amount of light reflected back to the tank.

 

There are several choices here, and will leave it to the DIYer to pick one that suits their budget.

  1. Polished Aluminum Sheets
  2. White Paint
  3. Reflective Mylar
  4. Aluminum Flashing
  5. Mirrored Plexiglass
  6. Aluminum tape for Ducts

Reflective Mylar can be obtained from a hydroponics store, art supply store or a hobby store. It is the material that is used to make the big shiny birthday balloons are made from. One problem with using reflective Mylar is its inability to withstand excessive heat. It will burn and melt when used too close to a MH lamp. Hence it is not suitable for use above the MH lamp, but does fine when used to line the side walls of the hood away from the lamp. Being a plastic material it does not corrode and can be easily wiped clean. The easiest way to attach it to the hood is by gluing it to the hood.

Polished Aluminum is another very commonly used reflecting surface. It is ideal for use behind the lamp, as it can withstand the heat well. It can be easily bent to make parabolic or elliptical shapes for reflectors. It can be fastened to the hood by using small metal screws. Polished aluminum may be available at your local sheet metal shops (check yellow pages), or purchased as precut sheets from the aquarium mail order business listed in the earlier sections. When using Aluminum sheet as a reflector in wooded hoods, it is a good idea to leave some clearance between it and the hood to allow air to circulate behind it and to prevent hot spots from potentially affecting the hood. An easy way to do this is to use a couple of washers behind the Aluminum sheet when attaching it with the screws.

Two other cheaper possibilities for use as a reflector are the aluminum flashing available at most home improvement stores and the shiny aluminum tape used for ducts (not the well known duct tape). The aluminum flashing is not polished, and will tend to corrode (get pitted with white Aluminum oxide deposits) over time and lose some of its reflecting capability.

MH Retrofit Kits

Another solution for the partial DIYer it to consider using a MH retrofit kit. Several aquarium stores and mail order businesses carry a pre-fab kit comprising a completely wired, ballast, socket, and reflector kit. These kits come in various configurations, ranging from ones where the set of parts is supplied as components, to those that are completely assembled ready to be mounted in a hood/enclosure. This completely assembled kit is an attractive option if you are not interested in sourcing and assembling the individual components and are only interested in making the hood. The picture, shows a complete MH retrofit kit, as sold by Reefers (www.acroproa.com). All it needs is a ballast, and a few screws to mount inside a hood. As usual, the trade off is in the cost and amount of DIY work involved, but these kits provide a good partial DIY solution.

Hood / Enclosure

Once you have acquired all the components, the next step is to design and build a hood/enclosure to assemble and house the components. A simple hood/enclosure can be fabricated out of wood, in the shape of enclosed box, with hinged openings to allow access into the tank and to the lights (see picture). Since a myriad of designs are possible depending on your skill as a wood worker, and aesthetic needs, this article will not get into the detail aspects of making the hood. Some key considerations are ventilation for heat removal and hinged openings for easy access to tank and lamps.

Concluding Remarks

One of the frustrations of a DIYer comes from the inability to speak and understand the jargon of the industry in a manner sufficient enough to locate the parts and the sources for the parts. I hope this article will get you over that hump, and provide you with basic knowledge with which to locate and hunt for cheaper sources and alternatives for components. And when you do find these, share with your fellow aquarists.

Please be careful when working around electricity and saltwater, check and double check your electrical installations and follow appropriate manufacturer guidelines. When in doubt, consult a qualified electrician.

Acknowledgements

Being a good DIYer requires fraternization with other DIYers, and I had the opportunity to interact with some good ones - Chris Paris, Brian Ferguson, Rod Andrews, James Wiseman, among others.