Metal halide (MH) lamps, as with all HID lamps, use a ballast to regulate circuit conditions – voltage, current, and waveform – for starting and operating the device.
A lighting ballast has three primary functions:
- establish an electric arc through the lamp
- limit current through the lamp after ignition
- compensate for variations in line voltage and ensure consistent lumen output
Core-and-coil vs. Electronic Ballasts
The first lighting ballast technology used to operate MH lamps were electromagnetic, also known also as a “core and coil” ballast for bulky, heavy, magnetic core of laminated steel plates wrapped in copper windings.
In the 1980s, more energy-efficient, solid-state, electronic ballasts were developed using semiconductors as the primary means to control lamp starting and operation.
There are four main reasons electronic ballasts are superior to electromagnetic ballasts:
- Increased light output increased – Electronic ballasts increase the mean lumen output of HID lamps. A 400 W metal halide lamp operated with an electronic ballast produced 15% more light output after 8,000 hours than the same lamp with an electromagnetic ballast.
- Use less energy to operate – A typical magnetic ballast for a 400 W metal halide lamp consumes 50–70 W, whereas an electronic ballast consumes as little as 5–20 W.
- Lamp life is up to 30% longer – Electronic ballasts keep MH lamps brighter for a longer period of time than the same lamps with magnetic ballasts, which lowers lamp replacement costs and makes them practical for high-bay, indoor applications.
- Provide dimming option – Electronic ballasts with dimming provide additional savings when full light output is not required. Some electronic ballasts are continuously dimmable down to 50% of lamp power.
Other benefits of electronic ballasts include:
- improved efficiency and color stability
- lower warm-up and restrike times
- smaller size and lower weight
- much less lamp flicker
- less lamp noise
- improved lumen maintenance
- elimination of harmonic distortion in the supply current
- the capacity to operate multiple luminaires off one ballast
Probe- and pulse-start ballasts
When lamps are cold, the ballast’s operating voltage may not be enough to create an arc and rely on two primary starting methods: probe-start and pulse-start.
Traditional MH lamps use probe-start, electromagnetic ballasts technology, which employs the use of two operating electrodes and a third, starting probe electrode in the arc tube.
Probe-start ballasts start lamps when it discharges a high open circuit voltage between the starting probe and one of the operating electrodes. Once the lamp is started, a bi-metal switch shuts off the starting probe electrode from the circuit.
Market demand for probe-start ballasts began to wane once industry realized the third electrode and other moving parts such as the switch led to inconsistencies in the lamp’s lumen and color output over their lifetimes.
The development of pulse-start electronic and electromagnetic ballasts, which create arcs by generating a high-voltage pulse using a circuit called an igniter, also moved industry away from probe-start ballasts.
Benefits of pulse start Metal Halide lamps
A metal halide lamp using an electronic ballast is about 70% more energy efficient than typical standard HID electromagnetic ballasts with probe-start metal halide lamps.
Probe-start/pulse-start differences
| Features | Probe Start MH | Pulse Start MH |
|---|---|---|
| Color | White | Brighter White |
| Efficacy (Lumens per Watt) | 60-85 | 90-110 |
| Lumen Maintenance | 65% | 75% |
| Lamp Life (hours) | 10,000 | 15,000 |
| Lamp Life (years) | 2.5 | 4.0 |
Source: Department of Energy
Other benefits of pulse-start ballasts include:
- lifetime of up to 15,000 hours – 50% longer than probe-start MH lamp of same wattage
- maintain higher, consistent CRI than probe-start ballasts
- superior cold-starting capability, starting at temperatures as low as -40°F
- re-start, referred to as re-strike, times can be four times as fast as probe-start MH lamps
MH lamp warm-up and restrike times
| Lamp/ballast type | Warm-up time (minutes) | Restrike time (minutes) |
|---|---|---|
| Probe-start/magnetic | 4 to 5 | 10 to 20 |
| Pulse-start/magnetic | 2 to 3 | 3 to 5 |
| Ceramic/magnetic | 2 to 3 | 10 to 20+ |
| Quartz pulse-start/electronic | 1 to 3 | 2 to 4 |
| Ceramic/electronic | 1 to 3 | 10 to 20+ |
Source: Department of Energy
New standards eliminate probe-start devices
The Energy Independence and Security Act of 2007 mandated significant changes for metal halide lighting fixtures using certain ballasts.
Starting in 2009, probe-start magnetic ballasts and lamps for operation of lamps up to 400 W were virtually eliminated from new luminaires to meet new efficiency standards.
The law requires a minimum ballast efficiency of 88% for pulse start ballasts and a minimum ballast efficiency of 94% for magnetic probe start ballasts. Compliant luminaires now bear a capital “E” printed in a circle on their packaging and ballast label.