Frequently Asked Questions
A: The lights which flicker are the high pressure sodium lamps. This type of lamp has a vapor of sodium inside, which in the presence of a sufficient voltage, will emit energy seen as light. This light has a yellowish color indicative of the sodium vapor inside. As the lamp approaches the end of life (insufficient vapors remaining for continuous operation), the lamp cycles from off to on to off, appearing to flicker. It’s a normal phenomenon which tells us it is time to replace the lamp.
Q: Some lights are bright white and others have more of a yellow glow. Why the difference?
A: The lights that appear to be a white light are called metal halide. They contain a vapor of mercury with some materials called halides that contain thallium, indium and sodium. When these materials are excited by the presence of a voltage, their normal state is raised to the point of luminescence and light is produced. Due to the composition of the elements contained within, the light contains most of the elements of the light spectrum and a white light is produced. Metal halide lighting is the best choice for pedestrian areas, as it provides a truer picture of colors and surroundings. This is especially true of sports lighting. Those lights that have a more yellow glow contain a vapor of sodium, which does not emit the entire light spectrum in luminescence. The High Pressure Sodium light source is much more economical and provides high light output for power input and thus is used in parking lots and roadway lights.
Q: What causes some of the “green boxes” on the campus to hum and is any harmful raidation emitted from these?
A: The boxes you are referring to are transformers. The humming noise is caused by “magnetostriction”, or a very small movement of the metal core of the transformer which is associated with the frequency of the impressed voltage on the transformer assembly. There is no radiation as the assembly is entirely encased and grounded. The hum is only a physical indication the transformer is working properly.
Q: What state and federal regulations do the Power Plants have to meet?
A: Our facilities rely on continuous air emissions monitoring equipment to ensure compliance with all State and Federal air quality requlations. For regulation information go to the North Carolina Department of Environment and Natural Resources, Division of Air Quality website.
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925 Branch St.
Chapel Hill, NC 27599