Part V: Everything You Need to Know About
Metal Halide Lamps and Ballasts


Metal halide (MH) lighting is often an intimidating choice for beginning reef aquarists and DIY enthusiasts alike. This article will provide basic background information on MH lighting systems, as well as an understanding of the basic vocabulary used when talking about metal halide lights, and the hardware components that make up a complete lighting system.

There are four basic components in any MH lighting system (not including the mounting hardware and wiring):

  • the lamp;
  • the ballast;
  • the socket and;
  • the reflector.

Metal Halide Lamps


Metal halide lamps are a type of HID (High Intensity Discharge) lamp; mercury vapor and high-pressure sodium lamps are also HID lamps. However, mercury vapor and sodium lamps are not typically used in the reef hobby but are widely used in the horticulture industry. The metal halide lamps used in the aquarium hobby are typically characterized and sold based on different attributes, such as:

  1. the manufacturer’s/lamp’s name;
  2. the lamp’s nominal wattage;
  3. the type of method used to mount the lamp, along with the number of ends in the sockets used to mount the lamps and;
  4. the lamp’s color temperature.

Metal halide lamps have two basic configurations; those with an outer envelope and those without. In the former, the lamp’s basic construction (see Figure 1) is an inner envelope (called the arc tube), which contains the arc, and an outer envelope (called the bulb) which filters out ultraviolet radiation (UVR) and shields the inner arc tube. These lamps are typically single-ended (SE) and use a threaded mount to screw into a socket. The second lamp configuration lacks the outer envelope and typically has two ends (double-ended, DE) that need to be inserted into a socket, as we shall discuss shortly.

The inner arc tube contains the electrodes and various metal halides, along with mercury and inert gases that make up the mix. The typical halides used are some combination of sodium, thallium, indium, scandium and dysprosium iodides. These iodides control the lamp’s spectral power distribution and provide color balance by combining the spectra of the various iodides used.

Figure 1. Anatomy of a typical mogul-based metal halide lamp (source Venture Lighting™).

Light is generated by creating an arc between the two electrodes located inside the inner arc tube. The inner arc tube is typically made of quartz, and this is a very harsh environment, with high temperatures approaching 1000°C and pressures of 3 or 4 atmospheres. To start a metal halide lamp, a high starting voltage is applied to the lamp’s electrodes to ionize the gas before current can flow and start the lamp. The outer jacket is usually made of borosilicate glass to reduce the amount of UV radiation emitted from the lamp. It also provides a stable thermal environment for the arc tube and contains an inert atmosphere that keeps the arc tube’s components from oxidizing at high temperatures.

Recently, some manufacturer’s catalogs have begun listing ceramic metal halide lamps. These refer to the fact that their inner arc tube is made of a ceramic material instead of quartz. Ceramic lamps can withstand higher arc temperatures and are supposedly better at holding the color temperature over the lamp’s life. To the best of my knowledge, no aquarium lamps currently are being sold with a ceramic envelope.

A characteristic of HID lamps is that they take several (from three to five) minutes to warm up, and during this warm-up period the light’s output varies in terms of intensity and color temperature. A lamp’s color temperature could take as much as 15-20 minutes after startup to stabilize. After any power interruption (1/20th of a second or more), a lamp that is hot will not restart immediately and must cool sufficiently before restarting. This time delay is called the restriking time and may take anywhere from 10-20 minutes for MH lamps.

As aquarists we are concerned with the characteristics that impact the selection of the lamp and its associated hardware. Metal halide lamps come in a wide variety of configurations differentiated by a number of factors: their wattage, their color temperature, their mounting base, their bulb’s shape, their electrical characteristics, their operating position, and their manufacturer. When working with a MH lighting system it is best to start by selecting the lamp first, and then selecting the other components based on the particular lamp chosen. In addition, some thought should be put into the types of lamps you may be using in the future. This has become more important recently, with many manufacturers of lighting systems selling specific ballasts for specific lamps.

The first choice to make is the wattage of the MH lamp to be used. Typical MH lamps are available in 70-watt, 100-watt, 150-watt, 175-watt, 250-watt, 400-watt and 1000-watt versions. The ones most commonly used for home aquaria are the 150-watt, 175-watt, 250-watt and 400-watt configurations, with the 70-watt lamps becoming more popular for nano reefs. The first determining factor in selecting the lamp’s wattage is dictated by the type of corals being kept, their light requirements and the aquarium’s depth. Generally speaking, for lamps with similar color temperatures, the higher the lamp’s wattage, the more light it produces.

Once the appropriate wattage has been determined, the next steps are to determine the type of lamp based on how it is to be mounted in the fixtures, and its starting requirements. The classifications that are commonly encountered in the reef hobby are single-ended (SE) and double-ended (DE). Single-ended lamps typically have a screw at one end and are designed to be mounted in a single socket. Double-ended lamps, on the other hand, are designed to be mounted in a pair of sockets, one at each end. Also, DE lamps do not have the large outer envelope typically found on single-ended lamps that is used to limit the lamp’s UV radiation. Double-ended lamps require an additional safety glass to be installed in the lamp’s fixture in order for them to be safe for your tank’s inhabitants.

Metal halide lamps are sensitive to the manner in which they are mounted, due to the sensitivity of the arc’s shape, in the arc tube. Lamps are designed to operate best only in a certain orientation. However lamps marked as “Universal lamps” can be operated in any position, but the lamp’s life and its light output are reduced when it’s used in an off-vertical position. For best performance, if the lamp’s operating position is known in advance, the position-oriented bulbs are best. Various codes are used to designate a lamp’s recommended burning position (e.g., U = universal, BH = base horizontal, BUD = Base up/down (vertical), etc.). Most modern aquarium lamps tend to be universal lamps and are usually used in horizontal burning positions. When using lamps in the horizontal position, it may be best to orient the lamp so that its exhaust tip (affectionately called the nipple) on the inner arc tube points up.

Starting Metal Halide Lamps


A metal halide lamp’s starting requirements are important because they impact the type of ballast that the lamp requires. Two methods are used to start MH lamps: probe start (standard start) and pulse start. Probe start refers to the method used to ignite the arc in the arc tube. A traditional or probe start metal halide lamp has three electrodes – two for maintaining the arc and a third internal starting electrode, or probe. A high open circuit voltage from the ballast initiates an arc between the starting electrode and the operating electrode at one end of the arc tube. Once the lamp reaches full output, a bi-metallic switch closes to short out the probe, thereby discontinuing the starting arc.

Pulse-start MH lamps do not have a starting probe electrode. An igniter in the pulse start system delivers a high voltage pulse (typically 3 to 5 kilovolts) directly across the lamp’s operating electrodes to start the lamp, eliminating the probe and bi-metallic switch needed in probe start lamps, as shown in Figure 2. Without the probe electrode, the amount of pinch (or seal) area at the end of the arc tube is reduced, which allows for increased fill pressure and reduced heat loss. Furthermore, using an ignitor with a lamp reduces tungsten sputtering by heating up the electrodes faster during starting, reducing the lamp’s warm-up time.

Figure 2. Two diagrams showing the difference between a probe start and a pulse start lamp design (source Venture Lighting™).

ANSI Lamp Designation


To provide a common system for identifying lamps, and to allow lamps to be cross-referenced with different manufacturers to select the proper ballast, the ANSI (American National Standards Institute) system is used to designate lamps. Designation of MH lamps that follow the ANSI system starts with “M” followed by a number (an “H” designation stands for mercury vapor lamps, and “S” for sodium lamps), which identifies the lamp’s electrical characteristics and, consequently, the appropriate ballast. After the lamp’s numbers are two letters that identify the bulb’s size, shape, finish, etc., excluding color. After this section, the individual manufacturer may, at its discretion, add any additional numbers or letters to indicate information not covered by the designation’s standard section, such as the lamp’s 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. A lot of European lamps are used in the hobby, and these do not exactly follow the ANSI standard but, instead, use the European standard, which, in some cases, may be slightly different from the ANSI standard.

Another term typically encountered in the aquarium lighting industry is HQI. HQI is a trademark of OSRAM, and stands for a specific brand of lamps made by OSRAM. The aquarium industry has been quite loose with this term and has applied it to any European metal halide lamp and now, even more loosely, to any DE lamp. European MH lamps do not directly conform to the ANSI standard and have different operating current and voltage requirements. In most cases, a direct match may not exist with U.S. ballasts, so the aquarium industry has tried to find ballasts that work with those lamps, and have labeled these as HQI ballasts. For example, the M80 and M81 ballasts are called “HQI ballasts” in the aquarium industry, for 150-watt and 250-watt lamp applications, respectively.

Table 1 shows a list of the available lamps frequently used in the hobby, along with their ANSI designations.

Table 1

Watts

Single or
Double-Ended

Base/ Mounting
Code

Starting Method

ANSI
Designation

150W

SE

Medium

Pulse

M102/M142

DE

Rc2

Pulse

M81

175W

SE

Mogul

Probe

M57

Pulse

M137/M152

250W

SE

Mogul

Probe

M58

Pulse

M138/M153

DE

R7

Pulse

M80

400W

SE

Mogul

Probe

M59

Pulse

M135/M155

Choosing the Color Temperature


The wattage, type of lamp (SE or DE) and starting requirements determine the ANSI code associated with the lamp (and the ballast). The aquarist next faces the choice of selecting the lamp’s color temperature. Lamps below 5000 Kelivn (K) are not usually recommended for use in reef aquaria. Desirable lamps in the hobby usually have color temperatures designated as 5500K, 6500K, 10,000K, 11,000K, 12,000K, 12,500K, 13,000K, 14,000K, 15,000K, 18,000K, 20,000K or 50,000K, with the generally loose understanding that the higher the lamp’s color temperature, the more blue its light output, however, this often is not the case.

Each lamp has its own spectral signature (how much light it produces at different wavelengths), and it’s important to remember that the ratings and color temperature supplied by aquarium vendors often do not correspond to the lamp’s actual output. Additionally, the lamp’s output is affected by the ballast used to drive it. It is the spectral characteristics and the intensity at different wavelengths that should be of greatest interest to reef aquarists. It is worthwhile to check the spectral characteristics of the lamps and ballast that you select by reviewing the data on the following website: www.reeflightinginfo.arvixe.com.

Lamp Bases


After the specific lamp has been selected, the next step is to check the lamp’s mounting base. The lamps most commonly used in the hobby are single-ended, 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. European lamps also have a mogul base, but it is slightly different from the E-39 and is called E40. The differences are small enough that the E40 base lamps will work fine in the typical E39 mogul base used in the U.S. Double-ended 150-watt lamps use the RSC (RX7s) base, while the 250-watt double-ended lamps use the Fc2 base. Figure 3 shows the various shapes and configurations of lamps and bases, along with the restrictions on their various operating positions.

Figure 3. Designations of various bulbs and bases, and operating positions
(source Venture Lighting™).

Figure 4. Deterioration of the arc tube and contents over time.

Metal halides lamps have a finite life and deteriorate with use. While the lamp may be rated for several tens of thousands of hours of use, in typical reef applications the lampsí output may drop by 30% or more in a year, necessitating a change of lamp. Several effects take place in these arc tubes that ultimately affect the lampís light output: deposits of electrode material build up on the arc tubeís wall, changes occur in the arc streamís chemical composition, the quartz deteriorates to a more crystalline form that is opaque to light, etc. Each time a MH lamp is turned on; tungsten sputters from its electrodes and, over time, blackens the arc tubeís wall. Figure 4 compares a new lamp (left) to a lamp used for over a year (right). The deterioration in the lampís arc tube manifests itself as a change in its spectrum, shifting the lampís color temperature toward lower Kelvin values. This is often referred to in the hobby as a spectrum shift, and results from decreased output at different wavelengths, with larger reductions at smaller wavelengths i.e. towards the blue end of the spectrum.

Ballasts


The ballast provides the proper starting voltage, operating voltage and current to the lamp to initiate and sustain its arc. High intensity discharge (HID) lamps have negative resistance, which causes them to draw an increasing amount of current; hence, they require a current-limiting device. The ballast provides the following functions:

  • It provides starting voltage and, in some cases, ignition pulses. All ballasts must provide some specific minimum voltage to ignite the lamp. In the case of pulse start lamps, an additional high voltage pulse is needed to ionize the gases within the lamp. These pulses are superimposed near the peak starting voltage waveform;
  • It regulates the lamp’s current and power. The ballast limits the current through the lamp once it has started. The ballast’s current is set to a level that delivers the proper power to the lamp. In addition, the ballast regulates the lamp’s current through the range of typical line voltage variations, thereby keeping the lamp’s power fairly stable to maximize the lamp’s life and performance and;
  • It provides appropriate sustaining voltage and current wave shape to achieve the lamp’s rated life. The ballast provides sufficient voltage to sustain the lamp as it ages.

Choosing the Ballast


Once the lamp is selected, the next step is to select the ballast that will be used to drive it. When putting together a MH lighting system, it is very important to match the ballast to the lamp(s). An easy way to do this is by using the ANSI designation. For example, when using a lamp designated M-57, look for a ballast with that same designation. For lamps with no ANSI designation, it is best to call the lamp’s manufacturer for their recommendation on the correct ballast to use. Table 2 shows a complete list of aquarium metal halide lamps and their ballast requirements as specified by their respective manufacturers. There is a trend in the reef aquarium hobby to use ballasts that do not match the lamp’s design specifications, often to “overdrive” a lamp, and hence, to generate more light output from a given lamp. This can lead to premature failure and shorter lamp life and, in some cases, explosive failure due to rupturing of the lamp’s inner and outer arc tube.

Table 2. Aquarium Metal Halide Lamps and Their Recommended Ballasts as Specified by Manufacturers (Compiled by Paul Erik Hirvonen).
70/75-watt MH DE Lamps

Lamp Standard

Lamp Type

Recommended
Ballast

Aqualine Buschke

HQI/M85

PULSE

M85

BLV

HQI/M85

PULSE

M85

Ushio

HQI/M85

PULSE

M85

Venture

HQI/M85

PULSE

M85/M98

150-watt MH SE Lamps

Lamp Standard

Lamp Type

Recommended
Ballast

Iwasaki 6500K Med

M102

PULSE

M102

Iwasaki 50,000K Med

M102

PULSE

M102

150-watt MH DE Lamps

Lamp Standard

Lamp Type

Recommended
Ballast

Aquaconnect

HQI/M81

PULSE

M81

Aqualine Buschke

HQI/M81

PULSE

M81

CoralVue

HQI/M81

PULSE

M81

Giesemann Megachrome

HQI/M81

PULSE

M81

BLV

HQI/M81

PULSE

M81

Iwasaki

HQI/M81

PULSE

M81

Radium

HQI/M81

PULSE

M81*

Sylvania

HQI/M81

PULSE

M81

Ushio

HQI/M81

PULSE

M81

Venture

HQI/M81

PULSE

M81/M102

XM

HQI/M81

PULSE

M81

* Note Radium Blue/20,000K (HRI-TS 150W/230/B/RX7S) is rated at 160W and may not operate on electronic ballasts with safety shutoff.

175-watt MH SE Lamps

Lamp Standard

Lamp Type

Recommended
Ballast

Aquaconnect 14,000K

Euro PS

PULSE

M137/M152

Aqualine Buschke 10/13,000K

Euro PS

PROBE*

M137/M152*

BLV Nepturion 10,000K

Euro PS

PULSE

M137/M152

CoralVue 10,000K, 14,000K, 20,000K

?

PROBE

?

CoralVue ReefLux 10,000K, 12,000K

?

PROBE

?

EVC 10,000K, 14,000K, 20,000K

M57

PROBE

M57

Hamilton 14,000K

M57

PROBE

M57

Helios 12,500K, 20,000K

M57

PROBE

M57

Iwasaki AQUA 2 15,000K

M57

PROBE

M57

PFO Lighting 11,000K, 18,000K

M57

PROBE

M57

Ushio Aqualite 10,000K, 14,000K, 20,000K

M137/M152

PULSE

M137/M152

Venture 5,000K,10,000K

M57

PROBE

M57

XM 10,000K, 15,000K, 20,000K

M57

PROBE

M57

* Note Aqualine Buschke 10/13,000K (175W SE) is a probe start lamp but is recommended for use on a pulse start ballast. A probe start ballast may not provide adequate sustaining voltage during warm-up and might cause cycling.
* Note Euro PS refers to low lamp current Pulse Start European specification.

250-watt MH SE Lamps

Lamp Standard

Lamp Type

Recommended
Ballast

Aquaconnect 14,000K

M80/HQI

PULSE

M80/HQI*

Aqualine Buschke 10/13,000K

?

PROBE*

M138/M153*

Blueline 10,000K+, 10,000K Superwhite

M58

PROBE

M58

BLV Topflood 5200K

M80/HQI

PULSE

M80/HQI*

BLV Nepturion 10,000K, 14,000K, 20,000K

M80/HQI

PULSE

M80/HQI*

BLV Colorlite Blue (20,000K)

M80/HQI

PULSE

M80/HQI*

CoralVue 10,000K, 14,000K, 20,000K

?

PROBE

?

CoralVue ReefLux 10,000K, 12,000K

?

PROBE

?

EVC 10,000K, 14,000K, 20,000K

M58

PROBE

M58

Giesemann Megachrome Marine 12,500K

M80/HQI

PULSE

M80/HQI*

Giesemann Megachrome Coral 14,500K

M80/HQI

PULSE

M80/HQI*

Hamilton 14,000K

M58

PROBE

M58

Iwasaki 6500K Clean Arc

M58

PROBE

M58

Iwasaki 6500K Clean Ace

H37

PROBE

H37

Osram Daylight (HQI-T 250W/D)

M80/HQI

PULSE

M80/HQI*

PFO Lighting Krystal Star 11,000K, 18,000K

M58

PROBE

M58

Radium Blue/20,000K

M80/HQI

PULSE

M80/HQI*

Sunburst 12,000K

M58

PROBE

M58

Ushio Aqualite 10,000K (UHI-S250AQ/10/CWA)

M58

PROBE

M58

Ushio Colorlite Blue/20,000K (UHI-S250/E39/BLUE)

M80/HQI

PULSE

M80/HQI*

Venture 5,000K,10,000K

M58

PROBE

M58

XM 10,000K, 15,000K, 20,000K

M58

PROBE

M58

* Note Aqualine Buschke 10/13,000K (250W SE) is a probe start lamp but recommended for use on a pulse start ballast. A probe start ballast may not provide adequate sustaining voltage during warm-up and might cause cycling.
* Note HQI refers to high lamp current European specification. Operating it on a standard American pulse start (ANSI M138/M153) ballast will reduce its output and may cause color shift.

250-watt MH DE Lamps

Lamp Standard

Lamp Type

Recommended
Ballast

Aquaconnect 14,000K

M80/HQI

PULSE

M80/HQI

Aqualine Buschke 10,000K, 20,000K

M80/HQI

PULSE

M80/HQI

BLV Nepturion 10,000K, 14,000K, 20,000K

M80/HQI

PULSE

M80/HQI

CoralVue 10,000K, 14,000K, 20,000K

M80/HQI

PULSE

M80/HQI

CoralVue ReefLux 10,000K, 12,000K

M80/HQI

PULSE

M80/HQI

EVC 10,000K, 14,000K, 20,000K

M80/HQI

PULSE

M80/HQI

Giesemann Megachrome Marine 12,500K

M80/HQI

PULSE

M80/HQI

Giesemann Megachrome Coral 14,500K

M80/HQI

PULSE

M80/HQI

Giesemann Megachrome Blue 22,000K

M80/HQI

PULSE

M80/HQI

Hamilton 14,000K

M80/HQI

PULSE

M80/HQI

Helios 12,500K, 20,000K

M80/HQI

PULSE

M80/HQI

PFO Lighting Krystal Star

M80/HQI

PULSE

M80/HQI

Phoenix Electric HexArc 14,000K

M80/HQI

PULSE

M80/HQI

Ushio Aqualite 10,000K, 14,000K, 20,000K

M80/HQI

PULSE

M80/HQI

XM 10,000K, 15,000K, 20,000K

M80/HQI

PULSE

M80/HQI

400-watt MH SE Lamps

Lamp Standard

Lamp Type

Recommended
Ballast

Aquaconnect 14,000K

HQI

PULSE

HQI*

Aqualine Buschke 10,000K

?

PROBE

M135/M155

BLV Nepturion 10,000K, 14,000K, 20,000K

HQI

PULSE

HQI*

BLV Colorlite Blue (20,000K)

HQI

PULSE

HQI*

CoralVue 10,000K, 14,000K, 20,000K

?

PROBE

?

CoralVue ReefLux 10,000K, 12,000K

?

PROBE

?

EVC 10,000K, 14,000K, 20,000K

M59

PROBE

M59

Giesemann Megachrome Marine 12,500K

HQI

PULSE

M135/M155/HQI*

Giesemann Megachrome Coral 14,500K

HQI

PULSE

M135/M155/HQI*

Hamilton 14,000K

M59

PROBE

M59

Helios 12,500K, 20,000K

M59

PROBE

M59

Osram Daylight (HQI-BT 400W/D)

HQI

PULSE

M135/M155/HQI*

Osram Daylight (HQI-T 400W BLUE)

Euro PS

PULSE

M135/M155

PFO Lighting Krystal Star

M59

PROBE

M59

Radium Blue (20,000K)

Euro PS

PULSE

M135/M155

Sylvania Aqua Arc 10,000K

M59

PROBE

M59

Ushio Aqualite 10,000K (UHI-S400AQ/10)

HQI

PULSE

M135/M155/HQI*

Ushio Aqualite 10,000K (UHI-S400AQ/10/CWA)

M59

PROBE

M59

Ushio Aqualite 14,000K, 20,000K

HQI

PULSE

M135/M155/HQI*

Ushio Colorlite Blue (20,000K) (UHI-S400BL)

M59

PROBE

M59

Venture 5,000K,10,000K

M59

PROBE

M59

XM 10,000K, 15,000K, 20,000K

M59

PROBE

M59

* Note Aqualine Buschke 10/13,000K (400W SE) is a probe start lamp but is recommended for use on a pulse start ballast. A probe start ballast may not provide an adequate sustaining voltage during warm-up and might cause cycling.
* Note HQI refers to high lamp current European specification. Operating it on a standard American pulse start (ANSI M135/M155) ballast will reduce its output and may cause color shift.
* Note Euro PS refers to low lamp current Pulse Start European specification. Operation on an HQI ballast is not advised by the manufacturer and will overdrive the lamp.

400-watt MH DE Lamps

Lamp Standard

Lamp Type

Recommended
Ballast

CoralVue 10,000K, 14,000K, 20,000K

HQI

PULSE

M135/M155/M108/HQI*

Hamilton 10,000K, 20,000K

HQI

PULSE

M135/M155/M108/HQI*

IceCap 10,000K, 20,000K

M108

PULSE

M135/M155/M108

Osram Daylight (HQI-TS 400W/D)

HQI

PULSE

M135/M155/M108/HQI*

PFO Lighting Krystal Star 11,000K, 18,000K

HQI

PULSE

M135/M155/M108/HQI*

Radium 5,200K (HRI-TS 400W/D/230/FC2)

HQI

PULSE

M135/M155/M108/HQI*

* Note HQI refers to high lamp current European specification. Operating it on a standard American pulse start (ANSI M135/M155) ballast will reduce its output and may cause color shift.

Ballast Circuit Types


Several different types of circuits are used for HID ballasts. Probe start and pulse start lamps need different ballasts. The different types of circuits used with standard MH lamps are Reactor (R), High Reactance Auto Transformer (HX-HPF), Constant Wattage Autotransformer (CWA), Super Constant Wattage Auto Transformer (SCWA), Constant Wattage (CW), etc. There are specific advantages and disadvantages to these different circuit types, and lamps may be designed to work with a specific type of circuit. It is not the intent here to discuss the various circuits and their utility, but rather to make the reader aware that there are differences in the circuit that pertains to how the ballast behaves with respect to variations in input voltage and also in their output to the lamps.

Most ballasts (except electronic ballasts) used for metal halide lighting are the CWA (constant wattage autotransformer) type. This is a lead circuit ballast and consists of a high reactance autotransformer (core-coil) with a capacitor in series with the lamp. However, ballasts for 150-watt and 250-watt DE lamps tend to be the HX-HPF circuit type and require an igniter along with the capacitor and core-coil. Ballasts for pulse start lamps also have an additional igniter to start the arc, and have their own set of ballast circuit types.

Capacitors are needed to improve a ballast’s (input) power factor, and are integral components of CWA and regulated lag circuits; they will not operate without capacitors. Both oil-filled (wet) and dry-film capacitor technologies are commonly used with ballasts. Oil-filled capacitors come in metal cases and are filled with a dielectric fluid; dry-film capacitors do not use a dielectric fluid. High intensity discharge lamp igniters provide a brief, high voltage pulse or pulse train to break down the gas between the electrodes of an arc lamp. Pulses can range from several hundred volts to 5kV. Typical durations are in the µsec range. They are usually timed to coincide with the peak of the open circuit voltage.

It is important to realize that a particular ballast specification corresponds to specific operational characteristics and, for proper functioning of lamps, it is important that the right ballast be used. To see the differences in the way ballasts operate lamps, compare the ANSI and European specifications (Table 3), which specify the arc operating voltage, current and required starting voltage (ignition voltage) / current for each standard/specification.

Table 3: ANSI and European Lamp/Ballast Requirements
(Compiled by Paul Hirvonen)

ANSI Code

Wattage Rating

Arc Operating Voltage

Arc Operating Current

Starting Method

Minimum Starting OCV For Lag (Reactor) Ballast

Minimum Starting OCV For Peak Lead (CWA) Ballast

Lamp Starting Voltage Pulse Height

Lamp Starting Current

Nominal Ratings

Vrms

Vpeak

Vrms

Vpeak

Min.

Max.

Min.

Max.

M58

250W

133V

2.1A

Probe Start

350

495

270

1.8 CF

N/A

N/A

2.1A

3.5A

M153

250W

133V

2.1A

Pulse Start

254

345

254

483

3.0kV

4.0kV

2.1A

3.2A

M80

250W

100V

3.0A

Pulse Start

230

325

TBD

TBD

4.0kV

6.0kV

3.0A

5.2A

250 HQI*

250W

100V

3.0A

Pulse Start

198

TBD

198

TBD

4.0kV

5.0kV

3.0A

4.5A

M59

400W

135V

3.25A

Probe Start

350

495

280

1.8 CF

N/A

N/A

3.2A

5.0A

M155

400W

135V

3.25A

Pulse Start

254

345

254

483

3.0kV

4.0kV

3.2A

5.0A

400 HQI*

400W

120V

4.0A

Pulse Start

198

TBD

198

TBD

4.0kV

5.0kV

4.6A

7.5A

*The 250 HQI and 400 HQI are European metal halide specifications which most single-ended and double-ended European lamps are built to.

The ANSI information in the table above was compiled from the following references:

  • ANSI M58 Document: ANSI C78.1378-1997
  • ANSI M153 Document: ANSI C78.01650-2003
  • ANSI M80 Document: ANSI C78.1387-2001
  • ANSI M59 Document: ANSI C78.1375-1997
  • ANSI M155 Document: ANSI C78.01650-2003

The ANSI specifications for universal operating position SE metal halide lamps are tested and rated with the lamp’s operating base up. These operating values vary with the lamp’s operating position. Operation of metal halide lamps below the limits of the ANSI standards will reduce the lamps’ efficacy and may result in color shift, arc instability, flicker and reduced lamp life. The lamp’s manufacturer should be consulted before operating metal halide lamps at reduced wattage or in applications using dimming circuits.

Ballast Configurations


Any ballast rated for the lamp it is designed for will function properly, but may come in different configurations, each with its pros and cons, as well as differences in prices and the amount of DIY work required. Several manufacturers’ ballasts 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. Ballasts for MH lamps are often available in a multi-tap configuration. This means that the same ballast can be used with different input voltages (e.g., 120/208/240/277) by selecting the right combination of wires leading into the transformer’s coil. The correct combination of wires to use for a specified voltage is indicated in the wiring diagram and is often labeled on the wires, too.

Figure 5. Components of a core-coil ballast.

(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. Core-coil ballasts are sold as kits, which include the transformer, capacitor (and ignitor, if needed) and mounting rails. These ballasts are the cheapest kind because they are mass-produced for commercial MH lighting purposes. Unfortunately, they are designed to fit into the standard housing of commercial lighting fixtures, meaning that a box will have to be found or fabricated to house the ballast. This is the ballast configuration typically found inside the commercially sold ballast boxes in the aquarium industry. Running these ballasts exposed is extremely dangerous and is therefore not a good idea.

(2) F-can Ballasts
The F-can ballast is very similar in appearance to the fluorescent ballast is potted in fluorescent type cans and utilizes asphalt based insulating materials. F-can ballasts may also have thermal protectors, which cut off power to the ballast if it overheats. These ballasts are also called tar ballasts due to the black asphalt based material used in their construction. Because these ballasts are already enclosed in a fluorescent type case, they are much easier to work with than core and coil ballasts, and can easily be mounted anywhere. Because these ballasts are designed for indoor use, they tend to have less "ballast hum." They are more expensive than core-coil ballasts, but their additional cost may be offset by the cost of the box and additional DIY work needed to install core-coil ballasts.

(3) Electronic Ballasts
Recently, electronic ballasts based on digital electronics have become available for metal halide lamps. Manufacturers claim that these ballasts provide better performance in a smaller package, have a high power factor, save energy, generate less heat, have less change in output power and have lower maintenance costs than F-can and core/coil ballasts. Manufacturers also claim that high frequency ignition reduces blackening on the arc tube’s wall, which gives better color stability and longer lamp life. In addition, electronic ballasts can dim the lamp up to 33% of its full light output. Two concerns with electronic ballasts operating at high frequency are acoustic resonance and electromagnetic interference. Several users have reported interference with other electrical signals, such as TV, and interference with home automation signals, such as those used for X10 devices.

Reflectors/Reflecting Surfaces


To maximize utilization of a lamp’s light output, 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. Several such reflectors are available commercially. Before using such a reflector, it would be wise 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 intend to add in the future. It is my experience that any reflector is better than no reflector, and that reflector designs do make a significant difference in how light is distributed over the tank. For more information on the differences between various reflectors, see the following list of articles.

  1. Joshi, S. and Marks, Timothy, 2003. Analyzing Reflectors: Part I - Mogul Reflectors. Advanced Aquarist, March 2003.
  2. Joshi, S. and Marks, Timothy, 2003. Analyzing Reflectors: Part II - Double Ended Lamp Reflectors. Advanced Aquarist, July 2003.
  3. Joshi, S. and Marks, Timothy, 2004. Analyzing Reflectors: Part III. Advanced Aquarist, March 2004.
  4. Joshi, S. 2004. Analyzing Reflectors: 400W DE Reflectors. Advanced Aquarist, Dec. 2004.

Acknowledgements


I would like to thank Paul Hirvonen for his comments and edits, and for providing the detailed information on the recommended ballasts for lamps (Table 2) and the ANSI ballast specifications (Table 3).



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Facts of Light – Part 5: Everything You Need to Know About Metal Halide Lamps and Ballasts by Sanjay Joshi - Reefkeeping.com