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Lamp Life Concerns Shouldn't Limit Use of Lighting Controls
September 20, 2011
Today's tip comes from James Piper, contributing editor for Building Operating Management magazine: Lamp life concerns shouldn't limit the use of lighting controls.
Fluorescent lamps have a rated service life that depends on a number of factors including how many hours they operate each time they are turned on. For example, a lamp with a 20,000 hour rated service life typically assumes that the lamp will operate for three hours per start. If they burn more than three hours every time they are started, their service life will increase, and vice versa.
In a typical office space, lamps are rated for a 20,000 hour service life based on a three hour operation per start. Assume that the lamps operate uninterrupted for ten hours per day. Using manufacturer's data, the service life of the lamps would be extended to approximately 26,000 hours, or 2,600 work days.
Let's assume that the lamps are turned off for just ten minutes per hour. Lamp life would be reduced significantly, to approximately 13,000 hours. Converting this to the equivalent number of work-days results in a service life of 1,560 days. But assuming an electricity rate of $0.12 per kWh, the savings by switching the lamps off ten minutes per hour would be approximately $12.48 over the life of the lamp. Even factoring in labor cost to replace the lamps, the energy savings exceeds the cost of reduced lamp life. And this was for one lamp with a relatively short turn-off period. Consider the savings that can be achieved for large areas where lamp operating time can be reduced by 50 percent.
Actual savings will vary with the number of times they lamp is started, the type of lamp and ballast installed, and the cost of electricity.
How often a lamp should be turned off is primarily dependent upon the cost of electricity. As a rule of thumb, if the space is to be unoccupied for more than ten minutes, it is beneficial to turn the lamp off. Facilities with particularly high electrical rates will benefit from turning the lamp off for periods as short as three to five minutes.
One way to hold down labor costs is through the use of a group relamping program. Group relamping programs can reduce the average labor cost of a single lamp replacement by 90 percent or more.