Ballasts

Lighting/Fan Control
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Receptacle
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Safty
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Locking / corrosion
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Ballast
Pot Light
Track Light
Exit Light
Fluorescent
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An electrical ballast (sometimes called control gear) is a device intended to limit the amount of current in an electric circuit.

Ballasts vary greatly in complexity. They can be as simple as a series resistor as commonly used with small neon lamps. For higher-power installations, too much energy would be wasted in a resistive ballast, so alternatives are used that depend upon the reactance of inductors, capacitors, or both. Finally, ballasts can be as complex as the computerized, remote-controlled electronic ballasts used with fluorescent lamps.

Ballasts are used where a load does not regulate its own current consumption well enough. These are most often used when an electrical circuit or device presents a negative (differential) resistance to the supply. If such a device were connected to a constant-voltage power supply, it would draw an increasing amount of current until it was destroyed or caused the power supply to fail. To prevent this, a ballast provides a positive resistance or reactance that limits the ultimate current to an appropriate level. In this way, the 'ballast' provides for the proper operation of the negative resistance device. Examples of such negative-resistance devices are gas-discharge lamps.

Ballasts can also be used simply to deliberately reduce the current in an ordinary, positive-resistance circuit.

An electronic lamp ballast uses solid state electronic circuitry to provide the proper starting and operating electrical condition to power one or more fluorescent lamps and more recently HID lamps. Electronic ballasts usually change the frequency of the power from the standard mains (e.g., 60 Hz in U.S.) frequency to 20,000 Hz or higher, substantially eliminating the stroboscopic effect of flicker (100 or 120 Hz, twice the line frequency) associated with fluorescent lighting (see photosensitive epilepsy). In addition, because more gas remains ionized in the arc stream, the lamps actually operate at about 9% higher efficacy above approximately 10 kHz. Lamp efficacy increases sharply to about 10 kHz and continues to improve until approximately 20 kHz.[1] Because of the higher efficiency of the ballast itself and the improvement of lamp efficacy by operating at a higher frequency electronic ballasts offer higher system efficacy. In addition, the higher operating frequency means that it is often practical to use a capacitor as the current-limiting reactance rather than the inductor required at line frequencies. Capacitors tend to be much lower in loss than inductors, allowing them to more closely approach an "ideal reactance".

Efficacy is the correct term and is the term used in this industry. Efficacy means "capacity or power to produce a desired effect" while "efficiency" refers to the ratio of power input vs power output. Since "lumen" is a measure of perceived light or the "desired effect" and not that of optical output of the lamp, term efficacy is used. A 60W fluorescent lamp with red phosphor producing 30W of optical power and the same wattage green phosphor lamp producing 30W of optical power would both have an efficiency of 50%, however the green lamp would have a higher efficacy due to the sensitivity of our eyes, a watt of green light has greater lumens than a watt of red light.

Two different fluorescent lamps of the same wattage could be giving off the same amount of photometric power within the visible spectrum, but could have different efficacy depending on the way it conforms to the way our eyes respond. The modern polychromatic lamps are designed on this concept. White light is made by blending individual color phosphors that matches the sensitivity of our eyes instead of emitting light in broad spectrum including where our eyes are not so sensitive.

Instant start

Starts lamps without heating the cathodes at all by using a high voltage (around 600 V). It is the most energy efficient type, but gives the least number of starts from a lamp as emissive oxides are blasted from the cold cathode surfaces each time the lamp is started. This is the best type for installations where lamps are not turned on and off very often.

Rapid start

Applies voltage and heats the cathodes simultaneously. Provides superior lamp life and more cycle life, but uses slightly more energy as the cathodes in each end of the lamp continue to consume heating power as the lamp operates.

Programmed start

More advanced version of rapid start. Applies power to the filaments first, then after a short delay to allow the cathodes to preheat, applies voltage to the lamps to strike an arc. Gives the best life and most starts from lamps. This is the preferred type of ballast for applications with very frequent power cycling such as vision examination rooms and restrooms with a motion detector switch.

Metal halide lamps require electrical ballasts to regulate the arc current flow and deliver the proper voltage to the arc. Probe start metal halide bulbs contain a special 'starting' electrode within the lamp to initiate the arc when the lamp is first lit (which generates a slight flicker when the lamp is first turned on). Pulse start metal halide lamps do not require a starting electrode, and instead use a special starting circuit referred to as an ignitor to generate a high-voltage pulse to the operating electrodes. American National Standards Institute (ANSI) lamp-ballast system standards establish parameters for all metal halide components (with the exception of some newer products).

A few electronic ballasts are now available for metal halide lamps. The benefit of these ballasts is more precise management of the lamp's wattage, which provides more consistent color and longer lamp life. In some cases, electronic ballasts are reported to increase efficiency (i.e. reduce electrical usage). However with few exceptions, high-frequency operation does not increase lamp efficiency as in the case of high-output (HO) or very high-output (VHO) fluorescent bulbs. High frequency electronic operation does however allow for specially designed dimming metal halide ballast systems.