The next few blogs will explain industry standards for determining the life of a particular lighting technology.
High Intensity Discharge (H.I.D.) lamps today consist mainly of Metal Halide and High Pressure Sodium. Low Pressure Sodium are not very common and Mercury Vapor technology is being phased out.
Manufacturer's will report a Metal Halide lamp, for example, has an 'Average Rated Life' of 20,000 hours. How is this determined and what exactly does it mean?
According to Philips Lighting, Metal Halide rated average life is the life obtained, on average, from large representative groups of lamps in laboratory tests under controlled conditions at 10 or more operating hours per start. It is based on survival of at least 50% of the lamps, and allows for individual lamps or groups of lamps to vary considerably from the average.
Metal Halide, in particular, are sensitive to the position in which it is being used. According to Philiips Lighting 2011 Lighting Catalog, a MS400/U/PS (Universal burn position-Pulse Start) has a rated average life of 15,000 hours. The same 400 watt metal halide with a specific burn position-MS400/BU/PS (Base Up-Pulse Start) has an average rated life of 20,000 hours.
Extreme temperatures and high or low operating voltages will have an impact on life of lamp, something not considered by the manufacturer when determining average rated life.
Venture Lighting, another Metal Halide lamp manufacturer adds, "Rated life does not account for the lumen depreciation, color shifting, and loss in efficacy that always occur as lamps age. To consistently provide a quality lighting system, you must not only consider the lamps that fail, but the lamps that continue to operate. Lower light output (lumen depreciation) occurs even though the lighting system continues to consume the same (or sometimes slightly more) electricity."
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