CFL Glossary of Terms

  • Compact Fluorescent Lamp (CFL): Also known as compact fluorescent light, energy saving light, or (less commonly) as compact fluorescent tube (CFT). It is a type of fluorescent lamp designed to replace an incandescent lamp; this means it can fit into most existing light fixtures formerly used for incancesdents.
  • Standard CLF Bulbs: CFL are compact because of the tiny fluorescent tube that was wounded into a spiral shape so it may fit in the shape and space of a traditional incandescent light bulb. Not surprisingly, CFLs are sometimes called mini-spirals, spirals or spring bulbs. The coiled tube can take the place of the standard bulb glass; it can also be placed inside a glass shell of a standard looking bulb to make it appear more conventional, in which case there is a modest loss of luminance. When selecting a CFL to replace an incandescent lamp, note the space the incandescent bulb fits into, as the equivalent CFL may be slightly bigger.
  • Globe CFL Bulbs: Most conventional globe bulbs are standard bulbs with an enlarged, globe-shaped glass. Since the glass is already enlarged in these conventional globe bulbs, the replacement CFL globe is usually exactly the same size. Most globe bulbs (incandescent and CFLs) are sold by the diameter of the glass globe.
  • Floodlight or Spotlight CFL Bulbs: Many homes today have recessed or built-in lighting that use a range of reflector bulbs. Reflector bulbs come in three primary sizes, R20 (small), R30 (medium), and R40 (large). Within each size, it is possible to get a range of different wattages. When other letters are prefixed to a reflector bulb’s designation, they refer to special aspects of the glass face or reflector shape. Common prefixes include BR (bulbous reflector) and PAR (parabolic aluminized reflector). The PAR bulb represents the high end of reflector lights and is designed both to provide a focused light (with little light spread) and to be used in damp locations (like showers or outdoors).
  • Candelabra or Tulip CFL Bulbs: Candelabras, sconces and smaller lamps often require a flame- or tulip-shaped bulb. Conventional versions of these bulbs come with either frosted or clear glass bulbs, with the latter meant to suggest a more flame-like appearance. Also, these bulbs come with both the small candelabra screw base and the medium Edison screw base. Presently, it is difficult for comparable wattage CFLs to match the small size of incandescent bulbs.
  • 3-Way CFL Bulbs: Standard CFLs do not work properly when used in a 3-way socket. A special, enhanced electronic ballast is built in to 3-way CFL bulbs to make them work properly in 3-way sockets. CFLs are now available in a full range of 3-way wattages and colors. These are most frequently available as spiral or spring bulbs. They work precisely like conventional 3-ways, but are somewhat larger. Higher wattage 3-way CFLs are usually sold with extension clamps to raise the lamp shade slightly in order to make more room for the larger CFL bulb.
  • Dimmable CFL Bulbs: Many wattages and styles of dimmable CFLs are now available. Even though dimmable CFLs generally work well, most dimmable CFLs will not dim to as low an illumination as a conventional incandescent bulb.
  • Shape & Size: Shapes of the bulbs can be separated into 6 different categories: standard, globe, floodlight or spotlight, candelabra or tulip, 3-way, and dimmable. A-19 is the archetypal light bulb shape and usually comes with a common screw base called a medium Edison base. While there are many color options for each prospective bulb replacement, the size, shape, or location of use may limit replacement possibilities. A key to avoiding frustration is to know the style and dimensions of each bulb you wish to replace.
  • Bulb Type: Typically a combination of the style of bulb as well as the width of the bulb. Usually, the first couple letters will indicate the type; “G” would indicate “Globe” and “PAR” would indicate “Parabolic Reflector.” The numbers indicate the diameter of the light bulb in eighths of an inch; a “G40” would be a “Globe” style that is “5 inches” in diameter.
  • Based Type: Part of the light bulb that either screws or snaps into a receptacle. Base type terminology may indicate common descriptive words like “Medium” or “Candelabra,” or may even contain numeric codes that signify size and variety, like “E26” or “2GX13.”
  • Average Lifetime (Hours): Average lifetime rating based on large quantities in test groups. This testing takes into account usage of 3 hours per start for fluorescent lamps and 10 hours per start for HID lamps.
  • Energy Used (Watts): Amount of energy required and used by a particular light bulb. It is an international system unit of power equal to one joule per second. Contrary to popular belief, the wattage of a bulb does not directly measure the brightness; the “lumens” of a light is what defines the actual light output.
  • Color Correlative Temperature (CCT): Kelvin number (ranging from 2,700 to 6,500) is a simplified measurement that indicates the general color emitted by a bulb. It generally measures the “warmth” or “coolness” of light source appearance.
  • Color-Rendering Index (CRI): Indicates how accurately the emitted light renders the color of illuminated objects. In other words, it measures a light source and grades its ability to render the color of objects “correctly,” as compared with a reference source with comparable color temperature. Scale ranges from 0 to 100 (i.e., 100 being perfect rendering). Recommended CRI: 80+ for homes, retail, restaurants, lobbies; 60-80 for offices, classrooms, supermarkets; and less than 60 for street lighting and warehouses.
  • Light Output (Lumens): Literal measure of the light-output of a particular light bulb, measured in the number of lumens (e.g., 600 lumens).
  • Volts: Voltage is a measure of electrical potential.
  • Length: Sometimes referred to as “Maximum Overall Length” or MOL. For light bulbs, it measures the absolute length of a light bulb, from the top of the bulb to the bottom of the base and is typically expressed in inches. For light fixtures, it applies to the complete vertical length of the fixture.
  • Width: Refers to the complete diameter of the widest point of the light bulb. For light fixtures, it applies to the widest horizontal point of the fixture.

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