In the Blink of a Lamp

During The winter holiday season, houses are often decorated inside and out with little blinking lights. But, when the regular house or commercial lights blink or flicker, that’s a different story, and it is about to change. The effect isn’t fully understood yet, though Congress has passed a law that will drive the change to newer lighting technologies. The Energy Independence and Security Act (EISA) of 2007 directs the Department of Energy (DOE) to undertake new energy conservation standards rulemakings, which includes amending previous rules with regard to general-service fluorescent lamps, incandescent reflector lamps and general-service incandescent lamps. While it doesn’t phase out incandescent lights by 2012 (as some articles have indicated), EISA established minimum efficiency and lifetime requirements, which apply to general-service incandescent lamps, requiring an improvement in the performance standard. This, basically, amounts to mandated phase-out.

Incandescent lamps are prone to light flicker when the voltage fluctuates, especially in the 1–20 hertz (Hz) range of fluctuations. It only takes a 0.3 volts root-mean-square (Vrms) variation at 8.8 Hz for most people to perceive that the light is flickering. Incandescent lamps are not an issue for harmonics or power factor, as they are nearly a pure resistive-type load. However, the biggest problem is the very low efficiency in converting electrical power to light output when compared to other types of lamps, with 90 percent of the watts (W) consumed given off as heat, not light. The technical term for the relationship between the light output, lumens and the power consumed (W) is called efficacy and is measured in lumens per watt (LPW). Incandescent lamps have an efficacy ranging from 15 to 20 LPW.

Fluorescent lamps have an efficacy ranging from 60 to almost 100 LPW. While fluorescent lamps have been used in commercial and industrial applications for years, these efficacy factors have driven the growth of a replacement for the screw-in incandescent lamp, i.e., the compact fluorescent lamp (CFL). CFLs last about 10 times longer than incandescent lamps and use about 75 percent less energy. Most currently available CFLs have electronic ballasts, which operate at much higher frequencies than the magnetic ballasts, which reduce the harmonic contributions historically associated with general-service fluorescents. Some older CFLs have magnetic ballasts, which is why some lamps flicker when you first turn them on.

“When compared to regular fluorescent lights with magnetic ballasts, the use of high frequency electronic ballasts (20,000 Hz or higher) in fluorescent lights resulted in more than a 50 percent drop in complaints of eye strain and headaches,” according to “Fluorescent Lighting, Headaches and Eyestrain,” a study published in Lighting Research and Technology, 1989.

CFLs aren’t without their drawbacks; for instance, they cost 3–10 times as much as incandescents. According to, CFLs also contain an average of 5 milligrams (a range of 0.9 to 18 milligrams) of mercury, which requires proper disposal and handling of breakages. Also, a recent study shows that the life span of a CFL can be reduced by as much as 85 percent under normal use due to switching on and off. And CFLs are nearly six times more expensive to make in terms of energy consumption.

Given that there is an AC-DC-AC converter in the base, there are current harmonics, and the power factor is less than unity (0.90 to 0.95). There is also the issue of infrared emissions during warm-up that can override the remote control systems for TVs, VCRs, DVD players, etc.

Another emerging technology lamp type using light-emitting diodes (LEDs) is about twice as efficient as CFLs and lasts 3–5 times longer than CFLs (or 50 times longer than incandescents). A 13W LED lamp produces 450 to 650 lumens, which is equivalent to a standard 40W incandescent lamp; some high-power LEDs (HPLED) can produce more than a thousand lumens. For comparison, there are white LEDs with luminous efficacy of 150, about double CFLs and 10 times that of incandescents. Depending on the design, they can have little harmonic currents and be virtually unaffected by voltage fluctuations (flicker-free). But, LED lamps are quite pricey now and will remain so until volume manufacturing makes more cost-effective solutions.

High-intensity discharge (HID) lamps include mercury vapor, metal halide (also HQI), high-pressure sodium, low-pressure sodium and less-common xenon short-arc lamps. With life spans of 24,000 hours and efficacy of 70–110, HID lamps claim the highest effectiveness and longest service life of any type of lamp. Having a ballast to start or ignite the gas within the lamp means that these also will have harmonic currents, though generally rated below 20 percent for the newer ones. Of all the aforementioned types of lighting, these are the only ones that have a “dark” period. In the case of a power failure, they will take several minutes to cool down, then several minutes to restart, and can take five minutes to warm up to full brilliance. And more so than CFLs, large mercury-vapor and metal halide lamps can contain more than 250 milligrams of mercury.

Depending on the requirements for cost, light output, harmonic current distortion, on/off cycling, life span and serviceability, there is a range of newer technology lamps to choose from when doing new construction and/or retrofit projects. And the majority of them will blink less when the voltage fluctuates.

BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.

About the Author

Richard P. Bingham

Power Quality Columnist

Richard P. Bingham, a contributing editor for power quality, can be reached at 732.248.4393.

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