The long bright white life of pulse start metal halide
When metal halide technology was introduced in 1964, it quickly leaped over the mercury lamp technology it was designed to replace. Metal halide lamps were more energy-efficient, had a higher color-rendering index (CRI), and had higher lumen maintenance than mercury lamps. But, metal halide lamps still suffered from several disadvantages-they took too long to start (and restart), the lumen depreciation curve was too steep, and color consistency was not good enough for more demanding white light applications.
Starting The first metal halide lamps were probe-start HID lamps like the mercury-vapor lamps they replaced. HID lamps with starting probes, or electrodes, can be started by a voltage generated by the ballast. This voltage is applied to the starting electrode through a resistor. A bi-metal switch inside the lamp disconnects the starting electrode once the lamp has warmed up.
High-pressure sodium (HPS) and low-wattage metal-halide systems do not have starting probes. Instead, they use a pulse starter to ignite the lamps. This method of starting is not new-what is new is its use in higher-wattage metal halide lamps.
Higher-wattage pulse-start metal halide represents the first new system technology in more than 30 years. It is called a breakthrough technology by some because it will drive the trend toward white light and replace the higher-wattage white light sources such as incandescent and halogen. The high degree of improvement resulting from adopting pulse-start technology is substantial enough to expect that it will quickly obsolete existing standard metal halide in the 175-W to 1000-W range.
Pulse-start system The old system compromises made to accommodate the probe starting method were eliminated with the design of the new pulse-start system. The pulse-start system consists of a new family of lamps, a reduced crest-factor ballast, and a separate pulse-start ignitor. There are significant performance improvements when upgrading to pulse start systems like higher lamp efficacy (lumens per watt), improved lumen maintenance, and faster warm up and restrike.
New lamp design The disadvantages of the old pinched seal arc tube lamps have been overcome with a new design-a formed body arc tube. There is no need for a starter electrode as found in standard, pinched arc tubes. Formed body arc tubes feature uniform geometry and higher fill pressures. The smaller pinch seals of the new arc tubes provide less heat loss, so temperature control is improved and lamp-to-lamp color shift is reduced. The new lamps can operate at lower ambient temperatures-about 10 degrees F lower than the pinched body lamps (-40 degrees F instead of -30 degrees F). The high mass pinch seal arc tubes have been replaced with a lower mass design, resulting in faster starting and restarting. These changes result in higher lamp efficacy (up to 110 lumens per watt), improved lumen maintenance (up to 80%), consistent lamp-to-lamp color (within 100 degrees K) and 50% faster warm up and restrike (three to five minutes vs. eight to 15 minutes), and longer life (20,000 hours).
Not all lamp manufacturers make all wattage lamps. Figure 1 shows the current status of lamp manufacturers and the lamps currently available. The old system compromises in ballast design have been eliminated with new ballasts designed to optimize pulse-start systems. The new ballasts take advantage of the lower open-circuit voltage requirement and the lower current requirement of the PS lamp. System performance is improved with lower ballast losses, higher system energy savings, and longer ballast life.
There are three new ballast types, the standard (super) CWA, for all voltages; the linear reactor, for 277-volt system only; and the premium regulated-lag ballast, for most voltages. Some of the linear reactor designs have the ignitor built in. The ignitor that supplies the high-voltage pulse to start the lamp is usually a separate component.
CWA (superCWA) A two-coil ballast, the CWA allows voltage transformation to allow its use on all voltages. The SuperCWA features lower crest factor than standard CWA (1.6 vs. 1.8). The advantages of this design include longer lamp life, improved lumen maintenance, and lower ballast losses. Lower ballast losses mean the ballast runs cooler, assuring that retrofits will not overheat.
For new installations or for relighting projects, the advantage of longer lamp life results in fewer fixtures, lowering first costs. For the end-user, the advantages of longer lamp life and lower ballast losses translate into reduced maintenance cost (with both lamp and ballasts lasting longer) and significant energy savings. For some applications the opportunity to rate the fixture at a higher ambient temperature may be important.
Linear reactor These single coil ballasts are designed to operate on 277 V ac mains. Reactor circuitry can reduce the normal ballast losses by approximately 50% by eliminating the need for voltage transformation. Combined with pulse-start lamps, they have system energy savings of 25%, with little or no light loss. They are designed to operate 150-W to 400-W pulse-start lamps on an input voltage of 277-V ac and use an ignitor to start the lamp. Strike time is less (two minutes compared to four minutes with standard systems), and restrike time is less-three to four minutes, compared with 15 to 20 minutes with standard. The linear reactor has the lowest current crest factor (1.4), which extends lamp life and reduces maintenance cost. The low crest factor also improves lumen maintenance, which translates to fewer fixtures.
Regulated lag ballasts (reg lag) These three-coil reg lag ballasts were primarily used for high-pressure sodium lamps until recently when they have been used to operate pulse-start metal halide lamps. This is a premium, specified ballast with excellent lamp regulation. A 10% change in line voltage will only change the lamp wattage 4% to 5 %, which improves lamp-to-lamp color consistency and allows greater voltage dips without extinguishing lamps. The size and cost of the reg lag ballast are higher than the CWA, and it is not designed for energy savings. However, low current crest factor of 1.5 can extend lamp life to 40,000 hours, reducing maintenance costs.
Electronic A few manufacturers of electronic ballasts have models that will operate pulse-start lamps. Unlike electronic ballasts for fluorescent lamps, they do not operate the metal halide lamps at high frequency, although the starting pulse may be high frequency. Advantages of metal halide electronic ballasts include improved lamp stability, including color consistency, and increased energy efficiency.
Mix and match Lamp safety requires that contractors and maintenance staffs ensure standard lamps are not installed on pulse-start systems. There is no physical way that prevents this accidental replacement, and the lamp could explode. There is no danger when pulse-start lamps are installed on standard systems; they simply will not light.
HID upgrades The trend is toward white light for both interior and exterior systems. This trend provides the opportunity to change high-pressure sodium (HPS) systems to metal halide systems by changing fixtures. Even standard metal halide systems that have recently been installed may be upgraded economically to pulse-start systems.
Pulse-start systems can be specified in new construction or retrofit projects. In addition to the performance improvements already outlined, additional benefits of using pulse-start systems in new installations include lower initial cost, maximum system efficiency, and an immediate return on investment.
Retrofit applications that can benefit from pulse-start conversions include: big box retail, manufacturing and industrial facilities, parking garages, area lighting and existing high-pressure sodium (HPS). For these applications, pulse-start systems can be used to either provide the same light for less energy or provide more light for the same energy. Figure 2 shows the same light, less energy scenario.
Note that two new sizes of pulse start lamps are available to compete with standard (universal) 400-W lamps and standard (BU) 400-W lamps. Figure 2 compares the pulse-start lamps with the standard lamps.
A retrofit of a gas station canopy. Relighting and retrofit solutions for a supermarket application (5200 burn hours) using 400-W pulse start systems with linear reactor ballasts is shown in Figs. 5 and 6. Contractors can benefit from additional work associated with the conversion of existing standard metal halide systems or high-pressure systems to pulse-start systems. The trend toward white light will only accelerate and the savvy contractor will sell their customers on the improvements resulting from the conversion to pulse-start metal halide systems.