Smart Buildings Systems for Architects, Owners and Builders

Incandescent light bulbs produce light by running electricity through a
metal filament inside a bulb which heats it and causes it to glow and emit visi-
ble light. When fluorescent lights are turned on electricity flows to two electro-
des on opposite ends of the lamp causing them to heat up. The electrodes,
which are very similar to a filament in an incandescent bulb, then become
hot and emit electrons that collide with and ionize noble gas atoms inside
the bulb. This creates a voltage difference between the two electrodes causing
electricity to flow between the two electrodes through the gas in the tube.
These gas atoms become hot vaporizing the liquid mercury inside the tube.
The mercury vapor then becomes excited and emits ultraviolet light which hits
a white phosphor coating that converts the ultraviolet light into visible light.
Due to an effect known as “avalanche ionization” (in which the gas con-
tinues becoming more excited and higher intensity light would be emitted until
the light failed) a device is necessary to regulate the electricity flowing through
the bulb. Thus, it is necessary to have a ballast to regulate current through the
gas. Modern ballasts supply the electricity needed to start the lamp and pro-
duce light, then regulate the current so that the lamp will produce the desired
light intensity (Fig. 4.5).
There are two main types of ballasts: magnetic and electronic. Magnetic
ballasts use electromagnetic induction to create the voltages used to start
and operate fluorescent lights. They contain copper coils that produce electro-
magnetic fields to control voltage. Magnetic ballasts, which have been used in
fluorescent lights since their origin, are considered outdated and are being
phased out by newer electronic ballasts. Electronic ballasts use solid-state cir-
cuitry, rather than magnetic coils, to control voltage to the lamp, making them
more energy efficient.

Argon

AC SUPPLY Gas

Mercury

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Electrode Starter

Switch

Phosphor

Coating

Pins

Ballast

Figure 4.5 Ballast.

Lighting Control Systems 55