DIY with Jon Garner

Metal Halide Lighting Components

Metal halide lighting systems are becoming more commonplace in the marine aquarium hobby, and many hobbyists have begun assembling their own systems to reduce startup costs. Unfortunately, many aquarists do not understand the purpose of the required components and are confused by much of the jargon associated with these types of lighting systems, making the task of choosing or modifying a metal halide system a potentially frustrating experience. This means that choosing or modifying metal halide lighting for a reef tank can be one of the most confusing aspects of constructing the entire reef aquarium system. In choosing this type of lighting system, there are many decisions to be made, and understanding the options and the technology involved should aid those aquarists attempting to upgrade their system.

Lighting for a reef tank must meet several different, and sometimes conflicting, requirements, including initial startup costs associated with purchasing and assembling the system components and the operating expenses associated with running the system and replacing failing components. Electrical consumption of the system, the useful life of the bulbs, and the bulb costs are perhaps the most overriding of these expenses. The main types of reef tank lighting are categorized by their types of bulbs, these are: Very High Output fluorescent (VHO), power compact (PC), metal halide (MH) and mercury vapor (MV). Metal halide and mercury vapor are in a class of lamps known as high-intensity discharge (HID) lamps, which rely on the evaporation of a solid material inside an arc tube to create light. Lamp manufacturers utilize a wide array of materials to create different color temperature lamps, and the availability and stability of these materials are the main contributors that impact the life and price of a bulb. In this article, only the metal halide and the Iwasaki mercury vapor lighting options will be discussed.

Metal halide or HID lighting systems consist of several different components, which may be purchased separately, as a retrofit kit, or as a completely assembled fixture. A metal halide lamp system consists of the lamp, socket or lamp holder, ballast, reflector and power cord. Additionally, there may be many unfamiliar terms, which add to the confusion. I hope that this article will help eliminate some of the confusion about metal halide system components and help you to select lighting system components that meet your needs. Some of the more common acronyms found in the lighting industry are listed in Table #1.

Metal Halide Lighting Acronyms

MH = Metal Halide
MV =Mercury Vapor
LPS =Low Pressure Sodium
HPS =High Pressure Sodium
HID = High Intensity Discharge, MV, MH, LPS and HPS
DE =Double-ended, most MH lamps in the U.S. are single-ended with a Mogul base
SE = Single-ended
HQI = Metal Halide Lamps with a high CRI and/or European DE and some SE lamps
OCV = Open Circuit Voltage
HX-NPF/NX-HPF = High Reactance Autotransformer
CWA = Constant Wattage Autotransformer
CW = Constant Wattage
CCF = Current Crest Factor

Acronyms Based on Bulb Position

BU = Burn the lamp with the base up
BD = Burn the lamp with the base down
HBU = Burn the lamp horizontal to base up
HBD = Burn the lamp horizontal to base down
V = Burn the lamp with the base vertical
U = Burn the lamp in any (universal) position
HOR = Burn the lamp with the base horizontal
Table #1

Lamps, Sockets, and Lamp Holders

In choosing lighting, it is generally accepted that increases in wattage result in increases in illumination. Consequently, the first thing to determine is what wattage lamp to use, and how many are going to be needed to provide thorough coverage for your tank. In most cases, one bulb is required per 1-2 ft2. Lamps are available in 70, 150, 175, 250, 400 and 1000-watt configurations, as well as color temperatures ranging from 4200K to 50,000K (see this article for interesting comparisons of various color temperature bulb combinations). There are three types of bases that are utilized to provide the main points of electrical contact to the bulb; these bases are known as mogul, medium, and double-ended. The most popular type of metal halide lamps in the U.S. are single-ended and have an E39 screw type base, which is commonly called a mogul base. Most European lamps imported into the US have an E40 screw base and are compatible with the E39 lamp holders. Some low wattage lamps (70 and 150 watt) use a medium base, which is the same size found in typical incandescent bulbs. There are also double-ended lamps that require a pair of lamp holders, known as Rx7S for 150 watt and Fc2 for 250 watt lamps. Many lamps need to be run in a particular spatial orientation to operate correctly and produce the proper spectrum with rated lifetime. Consequently, lamps are marked, usually on the outer sleeve, by the position in which they need to be operated, such as Base Up (BU) or Base Down (BD), Horizontal (H), Vertical (V), etc. A complete listing of the various lamp position options is found grouped at the bottom of Table #1.

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Mogul Base
Fc2 DE Lamp Holder
Rx7S DE Lamp Holder


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175 watt Mogul base
DE150 watt HQI

Metal halide operation can be broken up into two separate phases, startup and steady-state operation, and the amount of power consumed by the system during these phases is different. Starting up the bulbs always requires more power than steady operation; up to several thousand volts may be needed. All MV and most MH lamps have an electrode located at one end of the arc tube to provide additional current to the lamp while it is starting up. These types of lamps require an Open Circuit Voltage (OCV), in which two times the lamp voltage is needed to initiate and sustain the arc. Some newer MH lamps (mainly European) have no starting electrode, so in addition to the OCV, the arc is started by a high voltage (4 kV or more) pulse that is provided by an igniter. Regardless of which type of lamp assembly is chosen, make sure to select a lamp socket that is pulse-rated high enough for the lamp that is being used (Table #2).

Unlike normal incandescent bulbs, HID lamps cannot be run directly off of 120 VAC like an incandescent lamp and take several minutes to warm up and come to full brightness. If the power is interrupted while an HID lamp is on, it will take several minutes to restrike the arc and cause the bulb to begin burning again. Restrike time is shown in Table 3 and describes the amount of time it takes for the lamp to cool down sufficiently to reinitiate the arc after power to the lamp has been lost.

Pulse rating for lamp sockets or holders:

Mogul base MH 175 - 400 watt 4KV
Mogul base MH 1000 6KV
DE base MH 70 - 150 watt 6KV
DE base 250 watt 5KV
Table #2


Lamp Type
Warm-Up Time
Restrike Time
5 - 7 minutes
3 - 6 minutes
2 - 5 minutes
10- 20 minutes
Table #3

There are a number of lamp manufacturers with a variety of wattage, color temperature and base styles available. Some of the more common ones are listed below.

Lamp Manufacturers:

Osram Sylvania
Aqualine Buschke (AB)
Ushio / BLV (in Europe)


A ballast in an HID system has generally two functions: 1) to provide voltage to the lamp so that it can initiate and sustain the arc, and 2) to provide the proper current to the lamp once the arc is started. Metal Halide lamps cannot be run directly off of 120 VAC like an incandescent lamp, because up to several thousand volts used to ignite the arc may be needed. The current must also be limited so that the lamp does not draw so much current that it destroys itself. Ballasts are typically of a Core & Coil, F-Can or electronic design. The Core & Coil is a transformer without a case along with a capacitor and igniter, if necessary. This can be a very economical choice, but it requires more wiring expertise and a metal box to house all of the components. This type of ballast will come as a kit with the coil, capacitor and igniter, if necessary. The F-Can and electronic ballast have all of these components in a pre-sealed rectangular metal box. The F-Can ballast looks just like a fluorescent lamp ballast, and it may also be called a tar ballast because of the tar-like material the can is filled with. The main problem with an F-Can ballast is that if one component such as the capacitor fails, you have to replace the entire ballast. A Core & Coil setup has a separate capacitor and igniter, so they can be replaced individually if one of them fails. The capacitor is the most likely component to fail.

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Core & Coil (w/capacitor)
Core & Coil
(w/capacitor & igniter)

Current Crest Factor (CCF) is another ballast parameter that should be considered because of its effect on lamp life, and it is a measure of the maximum amount of current that is sent to the bulb. The lower the CCF is, the longer the lamp will last because there is less stress on the electrode. Table #4 below shows the CCF for several types of ballasts. Electronic ballasts often have the CCF listed in their ballast specifications.

Ballast Current Crest Factors (CCF)

European Reactor ~ 1.5
Standard CWA (capacitor in series with the lamp) ~1.8
CWA and Super CWA (capacitor in parallel with the lamp) ~1.6
IceCap 150 watt MH < 1.5
IceCap 250 watt MH HQI < 1.8
IceCap 400 watt MH < 1.8
Table #4

The line voltage that the ballast is plugged into will have an effect on the lamp voltage and, therefore, it's light output. Autotransformer type ballasts tend to drop the lamp voltage when the line voltage drops. If the ballast is rated for 120 VAC and it is run on 110 VAC, the lamp will also not be running at full power and so the spectrum and intensity will vary. If a constant wattage autotransformer (CWA) type ballast has a +/- 10% change in line voltage, the lamp wattage will also vary by +/- 10%. A constant wattage (CW) type ballast has the best regulation, in which a +/- 13% line voltage change only produces a +/- 2% lamp wattage change. From these numbers it becomes obvious that the line voltage on which the ballast operates is a very important factor in maintaining the lamp wattage. If the circuit that the ballast is on also carries pumps, heaters, a chiller, etc., then the line voltage may be lower than expected, causing the lamp to discharge at a much lower intensity than expected. A separate circuit may be a good idea for the ballast in this situation, and if several high wattage ballasts are being used, then more than one circuit may be necessary for proper operation. Most ballasts come without a power cord, so one will have to be connected. Use a three-prong plug so that the frame can be grounded. If the ballast needs to be turned on and off manually, then a power switch should also be installed. Maximum wire lengths (listed in Table #5) should be adhered to for proper operation of the ballast.

Wire size and maximum lengths (in feet) for ballasts without an igniter


*Igniter based systems should limit lamp to ballast wires to 5' or less.

Table #5

To help select the proper ballast for the lamp that has been chosen, the American National Standards Institute (ANSI) issues a number for each lamp and base type. These standard numbers simplify matching the lamp to a socket (or lamp holder) and the ballast transformer needed to drive it. The ANSI number for a metal halide lamp starts with an M followed by two to three digits. The ANSI number for the Iwasaki mercury vapor lamp starts with an H followed with two digits. There may be many other letters and numbers that are part of the manufacturer's part number on the lamp, but for our purposes, they are of little significance. A ballast transformer for a lamp can be chosen by matching the ANSI number of the lamp to the same ANSI number of the ballast. The socket or lamp holder ANSI number can also be used to choose the proper socket or lamp holder for the lamp. Knowing these ANSI numbers will ease the task of matching the components. Not all lamps are marked clearly, so there is a matching lamp to ANSI number (see Table #6 below).

ANSI Numbers for Popular HID Lamps and Sockets/Lamp Holders

150Watt Metal Halide Ballast ANSI code M81
150 BLV/Ushio 10,000K Double-Ended RX7s Lamp Holder
150 AB 10,000K Double-Ended RX7s Lamp Holder
150 Radium Blue 20,000K Double-Ended RX7s Lamp Holder
150 Osram Daylight Double-Ended RX7s Lamp Holder
150Watt Metal Halide Ballast ANSI code M102
150 Iwasaki 6500K Single-Ended Medium
150 Iwasaki Aqua 50,000K Single-Ended Medium
175Watt Metal Halide Ballast ANSI code M57
175 Venture 5200K Single-Ended E39 Socket
175 Venture 10,000K Single-Ended E39 Socket
175 Ushio 10,000K* Single-Ended E39 Socket
175 AB 10,000K* Single-Ended E39 Socket
175 Sunburst 12,000K Single-Ended E39 Socket
250Watt Metal Halide Ballast ANSI code M58
250 Venture 5200K Single-Ended E39 Socket
250 Venture 10,000K Single-Ended E39 Socket
250 Ushio 10,000K* Single-Ended E39 Socket
250 AB 10,000K* Single-Ended E39 Socket
250 Sunburst 12,000K Single-Ended E39 Socket
250Watt MV ANSI code H37
250 Iwasaki 6500K Single-Ended E39 Socket
250Watt Metal Halide Ballast ANSI code M80
250 Ushio 10,000K Single-Ended E39 Socket
250 AB 10,000K Single-Ended E39 Socket
250 GE Daylight Single-Ended E39 Socket
250 Radium Blue 20,000K Single-Ended E39 Socket
250 BLV/Ushio 10,000K Double-Ended Fc2 Lamp Holder
250 AB 10,000K Double-Ended Fc2 Lamp Holder
250 Osram Daylight Double-Ended Fc2 Lamp Holder
400Watt Metal Halide Ballast ANSI code M59
400 Venture 5200K Mogul Single-Ended E39 Socket
400 Venture 10,000K Single-Ended E39 Socket
400 BLV/Ushio 10,000K* Single-Ended E39 Socket
400 Ushio Blue 20,000K USA Single-Ended E39 Socket
400 AB 10,000K* Single-Ended E39 Socket
400 Sunburst 12,000K Single-Ended E39 Socket
400Watt Mercury Vapor Ballast ANSI code H33
400 Iwasaki 6500K Single-Ended E39 Socket
1000Watt Metal Halide Ballast ANSI code M47
1000 Venture 5200K Single-Ended E39 Socket
1000 Coralife 20,000K Single-Ended E39 Socket
1000 Sunburst 12,000K Single-Ended E39 Socket
*Not optimal ballast for lamp
Table #6

Another useful resource can be found on the Advance Transformer's web site; it features a search engine that displays a list of ballast transformer model numbers that match the ANSI number of the lamp. An Acrobat PDF document containing a data sheet is available for each type of ballast that shows all of the parameters for the ballast as well as diagrams, which demonstrate how to wire the ballast to the lamp, capacitor and igniter, if required. They also have a PDF document entitled Pocket Guide to High-Intensity Discharge Lamp Ballasts that contains a lot of useful information for the potential do-it-yourselfer, including a troubleshooting guide.

There are a number of ballast manufacturers that make different styles of ballasts. Some ballasts only operate on one input voltage, while others are multi-tap and operate on several different input voltages by connecting the line voltage to the wires designated for that particular voltage. Check the ballast specifications very carefully to make sure the ballast will meet your needs and voltage range for the lamp.

Ballast Manufacturers:

Advance Transformer
Universal Lighting Technologies (previously Magnatek)
Sola Ballast
IceCap (electronic)
LN (electronic)

Additional Components

A reflector will reflect more of the light downward, so that it ends up in the tank instead of on the ceiling and floor. Additionally, a good reflector can dramatically increase the spread and distribution of light while also minimizing the amount of light that is reflected back towards the bulb. Pre-made reflectors are available such as the SpiderLight™ parabolic reflector or the PFO Optimal Reeflector™. Custom-made reflectors may be obtained from Aquatic Technology, where they will cut and bend spectral aluminum to your specifications. As a fairly effective substitute for a reflector, the inside of the lighting fixture or canopy may also be painted white, or lined with a reflective material. Due to the intense heat generated by metal halide systems, fans may also be required to keep the tank from over-heating. Fans are available from electronics suppliers and most aquarium businesses that sell lighting components. However, do not blow cool air directly over the lamps, as bulb cooling will result in inefficient evaporation inside the arc tube and abnormal spectral variations of the bulb will result. It is important to remember that these bulbs are designed to operate at a pre-determined temperature.

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SpiderLight™ reflector


Being armed with the knowledge of the acronyms and the manufacturer's model numbers for the ballast and socket will allow you to use an electrical supply house, or the Internet, to make a more informed purchase of metal halide components. The tables provided in this article will help match the different components. If you are not completely comfortable working with electrical wiring, please get a qualified electrician to help you, or purchase a complete lighting fixture or retrofit kit. Many of our sponsors carry both components and complete lighting fixtures.

If you have any questions about this article, please visit my author forum on Reef Central.


Paul Erik Hirvonen contributed information and pictures to this article.

Websites with more information:

Universal Lighting Technologies

IceCap, Inc.

Sola Ballasts

Ushio America, Inc.


Eye Lighting International of North America (Iwasaki)



Reef Central's DIY Links

Paul Erik Hirvonen's Lighting Information Site

Spectral Analysis of MH Lamps - Do ballasts make a difference by Sanjay Joshi & Dave Morgan

Spectral Analysis of Metal Halide Lamps Used in the Reef Aquarium Hobby Part 1: New 400-watt Lamps by Sanjay Joshi & Dave Morgan

Spectral Analysis of Metal Halide Lamps Used In The Reef Hobby - Part 2 by Sanjay Joshi & Dave Morgan

Spectral Analysis of Metal Halide Lamps Used in the Reef Aquarium Hobby Part 3 - 250-Watt Metal Halide Lamps by Sanjay Joshi & Dave Morgan

Product Review: The Digital Ocean SpiderLight™ Reflector Kit by Richard Harker

A Look at 400-watt Metal Halide Bulbs and Ballasts by Gregory Schiemer

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