And there are also screw-in forms of fluorescent lamps that fit the sockets on standard light fixtures and in floor and table lamps. Known as CFL (compact fluorescent light) bulbs, they were regarded as an excellent energy-saving alternative to incandescent bulbs—at least until the advent of LED technology. Fluorescent tubes (officially known as “lamps”) come in five basic types, identified as T2, T5, T5HO, T8, and T12, and The “T” designation stands for “tubular,” and the following number refers to its diameter in 1/8-inch diameter increments. A T12 bulb, for example, is 12/8 inch in diameter, or 1 1/2 inches. A T2 bulb, on the other hand, is 2/8, or 1/4 inch, in diameter. Here’s what you should know about each basic fluorescent tube size.
Fluorescent Tubes vs. Fluorescent Bulbs
In a fluorescent tube, there is an electrode at either end of the tube. A device known as a ballast steps up the 120-volt line current in the circuit to a level sufficient to energize the mercury vapor within the tube. The electron flow moves from the electrode at one end of the tube to the electrode at the other tube, and light is produced as ionized mercury atoms strike the powdered phosphor that lines the inside of the tube. A screw-in fluorescent light bulb is essentially a miniaturized version of the long bulbs used in shop lights and similar fixtures. In the bulb version, a miniaturized ballast is integrated into the base of the screw-in portion of the bulb. Most screw-in fluorescent bulbs consist of small T2 tubes tightly coiled together so that the bulb remains roughly the size of a standard incandescent light bulb. In CFL bulbs that screw into standard light fixture sockets, the ballast that steps up current is integrated into the screw-in base rather than placed in the light fixture itself. This allows the CFL bulb to be used in standard light fixtures that can also accept incandescent or LED bulbs. Be sure to do your due diligence before making a selection of light fixture, especially if you need a cold weather-start light fixture. A rapid-start, instant-start, or electronic type ballast may be the right choice for you. Your local dealer can help you choose the right fixture if you give him or her the parameters of your needs for your installation. These are now less popular as users have migrated smaller and more efficient T5 and T8 tubes. Older factories are seeing the benefits of moving away from these older style tubes, and with the new age of LED lighting, it looks as though the days of these old-style fluorescent tubes are numbered. The tube diameter, as defined by the T rating, is just one element that goes into choosing a fluorescent tube. There are several other considerations when it comes to matching a fluorescent tube to a specific fixture:
Wattage: Light fixtures will be rated for the wattage of fluorescent tubes they accept. This will vary according to the diameter and length of the tube. For example, T12 bulbs are typically 48 inches long and use 40 watts to provide 2500 lumens of light output. T5 bulbs, on the other hand, are typically about 45 inches long and use only 28 watts to produce the same 2500 lumens of light output.Light output (Lumens): This is a measure of the amount of illumination provided by the fixture. The higher the number, the brighter the light.Color rendering index (CRI): This refers to the color of the light produced, on a 100-point scale, where 100 is the relatively warm light produced by standard incandescent light bulbs. CRI ratings under 70 tend to produce a greenish color that’s not all that pleasing. For most residential use, ratings of 80 to 89 are considered best. T12 tubes generally have a CRI of about 62, while T5 and T8 tubes have a more realistic CRI of 85.Correlated color temperature ( CCT): is a measurement of the color appearance measured in degrees Kelvin within a range of 2700K to 6500K. 2700K is the warmest (closest to yellow) and 6500 is the coolest (closest to sunlight). Most light fixtures will allow you choose tubes with different CCT ratings. If you are using the fixture as a grow light for plants, for example, you’ll want to choose one with a color temperature close to natural sunlight.Shape: Your light fixture may accept traditional straight tube, or it may be designed for curved or round tubes. CFL (compact fluorescents) have narrow tubes that are coiled to create a shape roughly the size and shape of traditional incandescent light bulbs, so that they can be used in standard light fixtures.Base type: Most common fluorescent light fixtures use bases with two pins that fit into slits in the light fixture. But CFL bulbs have screw-in bases that fit standard light fixtures. And there are also single-pin tubes designed for fixtures with that socket design.
For example, a typical fluorescent tube might carry a designation such as this:F/32/T8/ Warm White/ Linear Fluorescent/ 3000K/ 28000 Lumens/ 48", interpreted as follows: F= “Fluorescent"32= 32 wattsT8= diameter (8/8, or 1 inch)Warm White= ColorLinear fluorescent=Tube shape3000K= Color temperature2800 Lumens=Light output48”= Tube length
