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How a Fluorescent Lamp Works
Fluorescent Basics
Lamp Types
Ballasts
Operating a Fluorescent Lamp
Fluorescent Color
Fluorescent Lamp Life
Fluorescent Efficiency
Fluorescent Basics
Fluorescent lamps consist of a phosphor-coated glass tube, which contains a small amount of mercury in a fill gas. When starting current flows through the electrodes, it creates an electric arc through the fill gas. This stimulates the mercury, which emits ultra-violet energy. This, in turn, stimulates the phosphors, which glow and produce white light.
In fluorescent lighting, the quality of the phosphors determines the color and quality of the light.
Fluorescent lamps require a ballast for proper operation and behave differently than incandescent sources.
Types of Fluorescent Lamps
Fluorescent lamps come in two basic types: linear and compact.
Linear fluorescent lamps, often called “tubes”, are tubular shaped, with a bi-pin base at either end. There are three common diameters for linear lamps, shown in 1/8’s of an inch. The wattage and light output of the lamp varies with its length. Linear lamps also require a ballast in the fixture.
Compact fluorescent lamps have a single base. The wattage and light output depend on the number of tubes on the base (twin, quad, or triple) and their length. Compact fluorescent lamps are often called CFL’s. There are two basic types of CFL’s. Pin-base CFL’s are used in dedicated fixtures with ballasts and special sockets. Retrofit CFL’s (also called integrated or screw-based CFL’s) are used in incandescent fixtures. They have an integral ballast and can screw into a standard socket.
ENERGY STAR qualified compact fluorescent lamps are available in a variety of wattages.
Ballasts
All fluorescent lamps need ballasts to start and operate. Each ballast is designed for a specific lamp (or group of lamps). And, a lamp will only operate properly on a compatible ballast.
There are two basic types of ballasts: magnetic and electronic.
Electronic ballasts – today’s standard – are best. They are efficient, mostly flicker-free, and quiet.
Magnetic ballasts emit a low-level hum, which many people find objectionable, and cause fluorescent lamps to flicker.
Advanced Technology GU-24 Line Voltage Socket with Pin-based lamp. The GU-24 socket is a relatively new type of socket that is being used by most major fixture manufacturers in their energy efficient product selections. The GU-24 accepts CFLs (with a GU-24 base) of a variety of wattages. Prior to the GU-24 you could not switch lamp types (lumen output and wattage) in a compact fluorescent fixture. Wattage and brands now can be interchanged.
GU-24 self ballasted lamps are similar to a screw-base compact fluorescent, but rather than using a screw-base, the integrated lamp/ballast connects to the GU-24 socket with pins. A simple twist will disconnect the ballast from the socket, making replacement easy.
Fluorescent Operation
Fluorescent lamps hesitate for a moment or two when starting. The length of the hesitation depends on the type of ballast. Older magnetic ballasts may also “pulse” a couple of times as they try to start the lamp. Newer electronic ballasts start more smoothly.
ENERGY STAR requires that lamps start within one second.
Fluorescent lamps are thermally sensitive. They produce maximum (rated) output at an ambient temperature of 77°F. If the temperature around the lamp is higher or lower, output drops. If the temperature is below 50°F, most ballasts will not start linear lamps. Compact fluorescent lamps generally start at 32°F.
Fluorescent Color
The colors we see in objects around us depend on the colors in the light sources that illuminate those objects. The color in the light source reveals the color of the object.
Fluorescent lamps are described by two color measures: Color Temperature and Color Rendering. The Color Temperature describes the appearance of the light - how “warm” or “cool” it appears. Color Temperature is measured in degrees Kelvin. 3000K lamps are called “warm”; 4100K are “cool”; and 3500K lamps are “neutral”. Color Rendering Index indicates how well a lamp reveals colors in objects. The best is 100. A CRI of 80 or better is good for residential applications.
Fluorescent Lamp Life
Fluorescent lamp life depends on how many times the lamp is started. Lamps are rated at three hours per start. (The lamps are turned on for three hours, then turned off for 20 minutes, then turned on again.) If fluorescent lamps are turned on and off more frequently, they will experience less than rated life.
Linear fluorescent lamps are rated at 15-30,000 hours (most at 20,000). Compact fluorescent lamps are rated at 6-12,000 hours. In residential applications, linear fluorescent lamps will generally last several years, or five-to-ten times as long as most incandescent sources.
Fluorescent Efficiency
Fluorescent lamps produce a lot of light, and they do so very efficiently. An F32T8 lamp is rated at about 2900 lumens, more than a 150 watt incandescent. A single two-lamp fluorescent fixture delivers more light than three typical incandescent “bowls”.
Fluorescent sources are also more efficient than incandescent. They achieve 50-100 lumens per watt (LPW), compared to less than 20 LPW for incandescent. (Note that comparisons between fluorescent and incandescent sources should include the power used by the ballast).
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