There are three main groups of lamp types available: incandescent, fluorescent, and high intensity discharge. Each lamp type has different characteristics that must be considered when choosing a lamp type for a particular application: color temperature, color rendering, efficiency, and lamp life. This article will look at fluorescent lighting.

The fluorescent lamp is made of a tubular bulb having an electrode sealed into each end and containing mercury vapor with a small amount of inert gas for starting. The inner walls of the bulb are coated with fluorescent phosphors. When voltage is applied, a flow of electrons – traveling at a high rate of speed – is driven from one electrode and is attracted to the other. Collisions between the electrons and the mercury gas atoms in their path cause a state of excitation which results in the emission of ultraviolet radiation; the fluorescent phosphors transform the ultraviolet rays into visible light. (The glass of the bulb allows light to pass through while allowing only a minimal amount of ultraviolet rays to pass through.)

Unlike an incandescent (also known as filament) lamp, a fluorescent lamp cannot be operated directly from the electric circuit. If it were, the lamp would not operate and when the discharge between the electrodes was established, the current would continue to rise until the lamp was destroyed. Therefore, each fluorescent lamp must use a device known as a ballast. The main function of the ballast is to limit the current and to regulate the voltage necessary to operate the lamp. There are two types of fluorescent ballasts available: the electromagnetic type and the solid state electronic type. The electromagnetic ballast has been used since the beginning of fluorescent lighting. The ballast, also known as "core and coil" type, consists of a core of steel laminations surrounded by two copper coils. This transforms the electrical power to control the lamps. In ballasts which are "high power factor," there is also a capacitor that improves the power factor.

The electronic ballast starts and regulates fluorescent lamps by using electronic components rather than the core and coil assembly. The basic advantages of the electronic ballast versus the core and coil ballast are increased efficiency, quieter operation, and cooler operation, which in turn reduces air conditioning costs.

Advantages

Two major reasons fluorescent lamps are a popular choice for many design applications are longer lamp life and higher efficiency. For example, compared with a 75-watt incandescent lamp which has an initial lumen (lumen refers to the amount of light that a lamp produces) output of approximately 750 lumens and a lamp life of 2000 hours, a comparable fluorescent lamp (18-watt compact) has an initial lumen output of about 1250 lumens and a lamp life of 10,000 hours. Note that the fluorescent lamp, while using 18 watts, produces more light than the incandescent lamp which uses 75 watts. Another factor to consider is that fluorescent lamps can be operated at 277 volts while most incandescent lamps must be operated at 120 volts. The advantage to using 277 volts is apparent on larger installations: by using 277 volts, a greater number of light fixtures can be connected to a circuit, thus reducing installation costs.

Most of the new fluorescent lighting installations use light fixtures with electronic ballasts. In fact, a typical four lamp fluorescent fixture using four 32 watt lamps with electronic ballasts consumes approximately 106 watts while the same fixture with standard 40-watt lamps using an electromagnetic ballast consumes approximately 176 watts.

Color

Color temperature and color rendering are two properties of lamps that can effect the way a space and the objects in that space appear to the eye. A warm color has a feeling of intimacy or coziness while a cool color has a more businesslike or institutional-type feeling. The color temperature of a lamp is based on the Kelvin temperature scale and is expressed in degrees Kelvin. Lamps that have a bright-white to blue-light appearance have a high color temperature (4000K and above) and are considered cool white. (Note that the color temperature pertains to the color of the light from the lamp and not actual temperature.) Lamps that have a yellow-white to a red-white color have a color temperature of 3000K and below are considered warm white. For comparison, incandescent lamps and candlelight have a warm color and a color temperature of about 2700K.

Color rendering is the measurement of how accurately a lamp renders the color of the objects it illuminates (compared with daylight). This measurement is known as the Color Rendering Index (CRI). It is based on a scale with a maximum number of 100 (daylight). A typical fluorescent bulb will have a CRI in the 80 to 90 range.