Average Rated Life
HID LAMP LIFE VERSUS OPERATING CYCLE
is the life value assigned to a particular lamp type. Statistically, Average Rated Life is a numeric value in hours of the median, (50% point), of a population of lamps that remain operating. For example, if a lamp had an Average Rated Life of 10,000 hours and 100 new lamps were installed in the same location, approximately 50 lamps would still be operating after 10,000 hours.
The starting process of HID lamps
place the highest level of stress on the lamp electrodes. Shortly after the arc tube fill gasses breakdown, the tungsten electrodes undergo a condition called sputtering. The sputtering condition vaporizes a small amount of the electrode, which is deposited on the arc tube inner wall. Tungsten deposited from the electrode on
the arc tube wall builds up as a black deposit resulting in reduced lamp lumens, higher arc tube wall temperatures and possible premature rupture of the arc tube. Electrodes of a HID lamp are designed to withstand operating cycles of 1 start every 10 hours to achieve the life rating of the lamp. Operating cycles less than 10 hours will result in shorter lamp life.
There are other factors that can impact HID lamp life, such as:
- type of ballast used,
- age and condition of the capacitor,
- lamp luminaire temperatures,
- operating position of the lamp.
HID lamps should only be operated in the position specified in the lamp literature or catalog. The following guidelines apply to the expected Average Rated Life when the lamp is operated with the recommended ballasts.
Published Average Rated Life is achieved using a 10-hour (on) operating cycle.
A five-hour operating cycle may result in achieving only 75% of the published Average Rated Life.
A two and one-half hour operating cycle may result in achieving only 50% of the published Average Rated Life.
WARNING: 24-HR OPERATING CYCLE
In applications where Metal Halide lamps are on a 24-hour operating cycle, 7 days a week, they are to be turned off once per week, for at least 1 hour. This is to prevent the remote possibility of a lamp rupturing and the heated components separating from the lamp, causing personal injury and, or property damage.