Tube Lights: Everything You Ever Wanted to Know (But Were Afraid to Ask)

Introduced in 1938, the fluorescent bulb was the first major lighting advance to achieve widespread commercial adoption following the 1905 introduction of the tungsten incandescent bulb.  Fluorescent bulbs represented a huge increase in efficiency and operating life over incandescent lamps, enabling cooler, brightly lit offices, factories, and schools, as well as home kitchens and baths. This article describes how tube lights work and explains some basic things you should know about fluorescent lighting.

Today, you can find two common types of tube lights:  fluorescent tubes and LED tube lights.  Until recently, the term “tube light” was synonymous with fluorescent light.  LED tube lights have begun to gain traction as a replacement for fluorescent lamps due to their ability to reduce electricity consumption, eliminate the requirement for toxic mercury, and significantly longer operating lives; however, the vast majority of tube lights are still the familiar fluorescent bulbs.  Some purists object to calling these lights “fluorescent tubes,” preferring to call them “fluorescent bulbs” or “fluorescent lamps,” but with the introduction of LED tube lights designed to replace the fluorescent bulbs in these fixtures, the use of the term “tube light” is becoming more common.

Fluorescent lamps are a type of gas discharge tube similar to neon signs and mercury or sodium vapor street or yard lights.  The basic concept behind a fluorescent lamp is that a flow of electrical current occurs between two metal conductors placed in a glass tube, a process also known as arcing.  The pair of metal connectors (electrodes) is sealed along with a drop of mercury in a gaseous phase and some inert gases (usually argon) at very low pressure inside the glass tube.  The inside of the tube is coated with a phosphor which produces visible light when excited with ultraviolet (UV) radiation.  The electrodes are in the form of filaments which for preheat and rapid or warm start fixtures are heated during the starting process to decrease the voltage requirements and remain hot during normal operation as a result of the gas discharge (bombardment by positive ions).

When the lamp is off, the mercury/gas mixture is non-conductive.  When power is first applied, a high voltage (several hundred volts) is needed to initiate the discharge.  However, once this takes place, a much lower voltage -usually under 100 volts for tubes under 30 watts, 100 to 175 volts for 30 watts or more – is needed to maintain it.

The electric current passing through the low pressure gases emits quite a bit of UV (but not much visible light).  The internal phosphor coating efficiently converts most of the UV to visible light.  The mix of the phosphor(s) is used to tailor the light spectrum to the intended application.  Thus, there are cool white, warm white, colored, and black light fluorescent (long wave UV) lamps.  There are also lamps intended for medical or industrial uses with a special envelope such as quartz that passes short wave UV radiation.

Fluorescent lamps are from 2 to 4 times more efficient than incandescent lamps at producing light at the wavelengths that are useful to humans.  As a result, they operate at a cooler for the same effective light output.  In addition, the bulbs themselves last a lot longer (10,000 to 20,000 hours versus 1,000 hours for a typical incandescent bulb).  However, for certain types of ballasts, this is only achieved if the fluorescent lamp is left on for long periods of time without frequent on-off cycles.

A fluorescent tube is incorporated into a fluorescent lighting system which may be a separate fixture or self-contained within a bulb as in the case of compact fluorescent (CFL) bulbs.  A fluorescent lighting system consists of two or three main components: (1) the fluorescent lamp (fluorescent bulb), (2) the ballast, and (3) the starter system. In addition, the system for a tube lamp includes a lamp holder and a switch.  Depending on the particular fluorescent lighting system, the starter may be a replaceable component, a starter may not be required, or the starter function may be integrated into the ballast. The starting function may also rely on the physical design of the fixture. To retrofit a fluorescent light fixture to support an LED tube light, the ballast (and the starter if a separate one is present) must be disconnected.

Let’s take a closer look at each of these components.  Turning first to the lamp holder, the most common is designed for the straight bi-pin base bulb.   The 12-, 15-, 24-, and 48-inch straight fixtures are common in household and office use.  The 4-foot (48″) type is the most widely used size.   Ballasts are available for either 1 or 2 lamps.  Fixtures with   4 lamps usually have two ballasts.  The modern electronic ballast performs two functions: current limiting and providing the starting kick to ionize the gas in the fluorescent tubes.  Older fixtures may have a starter.  The starter is a device to initiate the electrode preheating and high voltage “kick” needed for starting.  Again, in most fixtures in use today, the ballast handles this function.  Finally, the switch provides on/off control unless connected directly to building wiring in   which case there will be a switch or relay elsewhere.  The power switch   may have a momentary “start” position if there is no starter and the ballast does not provide this function.

An LED tube light is radically different in design and operation from a traditional fluorescent lamp.  The LED tube light consists of four essential components: the LED circuit board, a heat sink and power supply, and a shell. The LED tube light contains no gas and does not require a ballast or starter. The LEDs themselves are semiconductors, and LED lights are often described as solid state lighting.

Fluorescent tubes are identified by several letters and numbers and will look something like “F40CW-T12” or “FC12-T10.”

The typical labeling you will see is of the form FSWWCCC-TDD (although, variations on this format are not uncommon):

Abbreviation	Meaning
F	Fluorescent lamp
WW	Nominal power in Watts (e.g., 4, 5, 8, 12, 15, 20, 30, 40)
CCC	Color (e.g., W=White, CW=Cool white, WW=Warm white, BL/BLB=Black light)
T	Tubular bulb
DD	Diameter of tube in of eighths of an inch (e.g., T8 is 1″, T12 is 1.5″)

Despite all of their advantages over incandescent lights, fluorescent lights due create some safety and environmental concerns.   Fluorescent and compact fluorescent lamps (CFLs), high intensity discharge lamps (HID) lamps contain a small amount of mercury and are identified with the elemental symbol Hg.  With the growing adoption of CFLs, there has been increasing awareness of the need to safely dispose of these bulbs.  In fact, ten states and multiple local jurisdictions prohibit the disposal of mercury containing products, including CFLs and other mercury containing lamps, in solid waste.  However, CFLs average less than 4 milligrams of mercury.  This is about the amount that would cover the tip of a ballpoint pen. By comparison, older thermometers contain about 500 milligrams of mercury, an amount equal to the mercury in 125 or more CFLs.  Still, given the shear volume of these bulbs that are thrown away each year, they result in a lot of mercury pollution.  The statistics are actually pretty staggering.  As of 2008, seventy-one percent of mercury-containing lamps used by businesses and 98 percent used in homes still were not being recycled. Each year, the lighting industry uses approximately 9 tons (8.2 metric tons) of mercury in manufacturing fluorescent lamps.  Of the 514 million lamps per year that enter the solid waste stream, about 142 million come from private homes and 372 million come from businesses, the government, and institutions. You can help eliminate this problem by looking for recycling options. Web sites such as Earth 911 and Light Recycle can provide local disposal options.

A more immediate danger is posed by the phosphor-coated glass on a broken fluorescent bulb.  If cut with fluorescent lamp glass, phosphor that gets into the wound can prevent blood clotting and will interfere with healing. Such injuries should be treated seriously and immediate medical attention should be obtained for people or pets that are cut. Medical personnel should be informed that the injuries were caused by a broken fluorescent lamp, and that mercury was present.

Ballasts can also overheat and fail.  Because a failing ballast can grow extremely hot, it can become a fire hazard. Modern ballast designs have an internal temperature sensor that shuts the ballast off it gets too hot. In most designs, when the ballast cools off, the sensor will allow the ballast to turn back on. A fixture where some or all of the lamps shut off by themselves and later come back on is probably a fixture with a failing ballast.

Finally, some research suggests that fluorescent lighting may trigger headaches, migraines and other physical symptoms. Research in England revealed that 100Hz fluorescent lighting creates an imperceptible flicker that can cause visual discomfort and make it more difficult to read accurately. Long-term clinical studies by the Irlen Institute have concluded that fluorescent lighting in schools may be related to many academic and health problems. A 2006 study by Capital E found that students in schools with natural light instead of fluorescent lighting had a 10 percent to 21 percent higher learning rate and higher test scores. A document prepared by the Irlen Institute reports that fluorescent lighting may trigger headaches, migraines and other physical symptoms.

The new LED tube lights appear to eliminate all of these safety and environmental issues, and we can expect to see them gradually replace fluorescent tube lights.

Tagged as: fluorescent tubes, Technology, tube lights