Do 100,000-Hour Induction Lamps Save Garage on Lighting Costs?
Donald R. Monahan, PE
Two new lamps are now available for parking facility lighting that offers a 100,000-hour lamp life. These lamps will survive four to six times as long as other parking facility lamp types, providing lamp life of more than 11 years for lights that burn 24 hours per day, 365 days a year. Parking facility owners may then experience a considerable reduction in re-lamp maintenance costs utilizing this new technology. However, does this reduced re-lamp cost justify changing? What are the other lighting characteristics of this new technology that impact parking facility lighting costs?
The new lamp is called an induction lamp. Osram Sylvania (Icetron Lamp) and Philips (QL lamp) currently manufacture induction lamps. The Icetron Lamp has a rectangular donut shape. The QL lamp has a typical "A" lamp shape similar to an incandescent bulb. The cost of the Induction Lamp is approximately $110 compared to $3 for a T8 fluorescent lamp or $30 for a 150W metal halide lamp.
Induction lamps are electrode-less fluorescent lamps. The system consists of three components -- the high frequency generator, the power coupler, and the discharge vessel (bulb). A 120-240 volt power supply is connected to the high-frequency generator, which sends an electronic current to an induction coil on the power coupler. The current passing through the induction coil generates an electromagnetic field, which excites mercury atoms in the gas fill of the bulb. The ionized mercury emits ultraviolet radiation. When struck by the UV radiation, fluorescent phosphors coating the inside of the glass bulb emit light. Since the system does not include electrodes or filaments, exceptionally long life is achieved with this new technology.
The rated life of the lamp is the number of operating hours at which 50 percent of a large number of tested lamps have survived. The rated lamp life for induction lamps is more than 100,000 hours. A survival rate of 90 percent occurs at 60,000 hours and a survival rate of 80 percent occurs at 80,000 hours. Philips guarantees the QL lamp for five years.
The light output of the lamp is measured in lumens. The higher the light output, the fewer the number of fixtures required to produce a given light level. The initial light output of a 165-watt QL induction lamp is approximately 12,000 lumens. Comparative lumen output for a 150-watt pulse-start metal halide lamp is 15,000 lumens. A 150-watt high-pressure sodium lamp has an initial light output of 16,000 lumens. An 8-foot-long fixture with four T8 fluorescent lamps will consume approximately 116 watts with an initial light output of 11,600 lumens. Therefore, the initial lumens of the induction lamp are somewhat lower than other typical parking structure lamp types at approximately the same wattage.
The light output of all lamps depreciates with the number of operating hours. One should then compare the maintained light output or lumens at the end of the rated life of the lamp. The light output at the end of the rated life of QL lamp is approximately 55 percent of the initial light output. At 60,000 hours, the light output is approximately 70 percent of the initial light output. Since most parking facility owners do not replace lamps until they burn out, the lamp lumen depreciation (LLD) at the end of the rated life should be used in the illuminance calculations.
The lumen depreciation at the end of the rated life of the induction lamp is substantially below the T8 fluorescent lamps (0.55 LLD vs. 0.88 LLD), and somewhat below the pulse-start metal halide lamp (LLD = 0.65) or HPS lamp (LLD = 0.73). When one takes into account other light loss factors for dirt depreciation, ballast factors and temperature factors, the maintained lumens for the QL induction lamp is significantly less than other parking facility lamp types. The net impact of the lower maintained light output at the end of the rated life of the lamp is that approximately 50 percent more induction lamp fixtures will be required compared to other lamp types to produce the equivalent illuminance.
The induction lamps add approximately $200 to the cost of a normal parking facility luminaire. In addition, very few fixtures are available for parking facility lighting that utilize the induction lamp. Therefore, the higher cost per fixture and increased number of fixtures will increase both the initial cost and the operational cost. Since the parking facility lighting operational cost is approximately two-thirds to three-quarters of the total lifecycle cost, one needs to determine whether the savings in maintenance cost will offset the higher operating cost and higher initial cost for the induction lamps.
Ignoring temperature effects, the average maintained illuminance on the floor for the fluorescent fixtures with four T8 lamps is approximately equivalent to the 150-watt pulse-start metal halide fixtures. However, the average maintained illuminance on the floor for the induction lamp fixtures is two-thirds of the fluorescent or metal halide fixtures at the same fixture spacing. The induction lamp has approximately the same light level as the other two, but requires 50 percent more fixtures.
The 25-year maintenance cost of the induction lamps is 51 percent of the maintenance cost of the metal halide lamp fixtures and 59 percent of the maintenance cost of the fluorescent fixtures even with 50 percent more fixtures. Therefore, one can see the benefits of the longer lamp life on the maintenance costs.
However, the initial cost of the induction lamp system is 2.3 times the cost of the fluorescent lighting system and 1.5 times the cost of the metal halide lighting system. The higher initial cost is due to a combination of the greater number of fixtures required as well as the higher unit cost per fixture. The operational cost of the induction lamps is more than double the operational cost of the fluorescent lamp fixtures and 30 percent more than the metal halide fixtures.
The higher initial cost and operating cost of the induction lamp fixtures more than offsets the savings in maintenance cost, when compared to a fluorescent lighting system or metal halide lighting system with equivalent illuminance. The total 25-year life cycle cost of the induction lighting system is 1.9 times the cost of the fluorescent lighting system and 1.25 times the cost of the metal halide lighting system.
If the technology of induction lamps advances to the point where the maintained lumen characteristics improve significantly, and the cost of the lamps decrease significantly, then induction lamps could be a viable alternate to metal halide lighting systems; however, it is not likely that induction lamps will overcome the advantage of T8 fluorescent lighting systems, particularly where cold ambient temperature is not a factor in the reduction of light output.
Donald R. Monahan, PE, is a consultant with Walker Parking Consultants/Engineers, Inc., in Denver, CO. He can be reached at firstname.lastname@example.org. There are a number of graphs and statistical charts that give detailed cost information on these products. PT didn't have room for them. If you are interested, drop Don an e-mail.
Article Abstract from March, 2003