What are some important characteristics of metal halide lamps?
Note: This is a complex question and has been separated into the following sections:
Color variation and color shift
Mid-wattage metal halide (MH) lamps have many characteristics that make them good choices for a variety of applications, including white light, energy efficiency, and long life.
Table 1 summarizes some characteristics of the technology available as of 2003. The information in the table has been compiled from manufacturers' literature.
(NOTE: Table 1 is available online as a separate PDF file by clicking the link below. If you obtained a printable PDF file of this report, Table 1 is at the end. )
Click here to view Table 1 "Characteristics of mid-wattage metal halide lamps."
Relative energy savings using mid-wattage MH lamps will depend on the application. Manufacturers' claims for the energy efficiency of their products rest on two assumptions:
- Although both probe-start and pulse-start MH lamps have high efficacies or lumens per watt (Figure 5), pulse-start MH lamps have higher rated efficacies.
- If pulse-start MH lamps indeed have higher efficacies and greater lumen maintenance than probe-start MH lamps, then for the same target illuminance, specifiers could use either lower wattage lamps or fewer luminaires than would be required for probe-start MH lamps. For example, manufacturers claim that a 320 watt (W) pulse-start MH lamp has similar initial light output as a 400 W probe-start MH lamp, so the same amount of light is achieved by using lower wattage lamps. Another option is to use fewer luminaires of the higher lamp wattage (400 W, for example) to achieve the target illuminance. In this case, it is important to follow the recommended luminaire spacing criteria to maintain a uniform light distribution. (See lumen maintenance section of this question).
|Figure 5. Initial lumens per watt for probe-start and pulse-start technologies