Fluorescent Lighting

Fluorescent lamps use 25%–35% of the energy used by incandescent lamps to provide the same amount of illumination (lamp efficiency of 30–110 lumens per watt). They also last about 10 times longer (7,000–24,000 hours).

Types of Fluorescent Lamps

Two general types of fluorescent lamps include these:

  • Fluorescent tube and circline lamps
  • Compact fluorescent lamps (CFLs)

Fluorescent Tube and Circline Lamps

The light produced by a fluorescent tube is caused by an electric current conducted through mercury and inert gases in the tube. The gas in the tube glows with ultraviolet light. This in turn excites a white phosphor coating on the inside of the tube, which emits visible light throughout the surface of the tube. It is important to note that much more mercury is saved from reduced electricity generation than is contained in fluorescent bulbs.


Fluorescent lamps require a ballast to regulate operating current and provide a high start-up voltage. Electronic ballasts outperform standard and improved electromagnetic ballasts by operating at a very high frequency that eliminates flicker and noise. Electronic ballasts also are more energy-efficient. Electronic ballasts do not contain PCBs (Poly-chlorinated Biphenols) as some of the magnetic ballast do. Special ballasts are needed to allow dimming of fluorescent lamps.


Improvements in technology have resulted in fluorescent lamps with color temperature and color rendition that are comparable to incandescent lamps.

The traditional/standard tube-type fluorescent lamps are usually identified as T12 (12/8 of an inch tube diameter). They are installed in a dedicated fixture with a built-in ballast. The two most common types are 40-watt, 4-foot (1.2-meter) lamps, and 75-watt, 8-foot (2.4-meter) lamps. Now, tubular fluorescent technology has improved. New products such as T8 and T5 are much more energy efficiency than T12 (T12 – 57 lumens/watt; T8 – 92 lumens/watt; T5 – 103 lumens/watt). Tubular fluorescent fixtures and lamps are preferred for ambient lighting in large indoor areas. In these areas, their low brightness creates less direct glare than incandescent bulbs.


Circular, tube-type fluorescent lamps are called circline lamps. They are commonly used for portable task lighting.

circline-lamps-2.jpg circline-lamps.jpg

Compact Fluorescent Lamps (CFLs)

CFLs combine the energy efficiency of fluorescent lighting with the convenience and popularity of   incandescent fixtures. CFLs fit most fixtures designed for incandescent bulbs and use about 75% less energy. Although CFLs cost a bit more than comparable incandescent bulbs , they last 6-15 times as long (6,000-15,000 hours).


CFLs work much like standard fluorescent lamps. They consist of two parts: a gas-filled tube, and a magnetic or electronic ballast. The gas in the tube glows with ultraviolet light when electricity from the ballast flows through it. This in turn excites a white phosphor coating on the inside of the tube, which emits visible light throughout the surface of the tube. Although CFLs are efficient and convenient to use, there are some challenges CFLs face and these include:

Premature CFL burnout: CFLs must last long enough for their energy efficiency to make up for their higher purchasing cost, what are the top three reasons for premature CFL burnout?

  • Frequent on/off switch - As anyone who frequently replaces CFLs in closets or hallways has likely discovered, rapid cycling can prematurely kill a CFL. Repeatedly starting the lamp shortens its life, because high voltage at start-up sends the lamp's mercury ions hurtling toward the starting electrode, which can destroy the electrode's coating over time.
  • Lighting fixtures are in areas that limit heat dissipation - Incandescents thrive on heat, the hotter they get, the more light you get out of them. But a CFL is very temperature sensitive. CFLs still generate significant amount of heat.  If lighting fixtures are in areas that limit heat dissipation, excess heat will cause premature burnout of the ballast.  For example, tightly enclosed ceiling fixture, recessed lighting fixture, "recessed cans"—insulated lighting fixtures—prove a particularly nasty compact fluorescent death trap, Among other things, these high temperatures can destroy the lamps' electrolytic capacitors—the main reason that CFLs fail when overheated.
  • Rough handling - There are a number of CFLs in the market that glass coils are directly connected to the ballast.  If you screwed into the based by holding on to the glass coils, you may cause the seal between the ballast and the thin glass tubes to crack.

Disposal of CFLs: Like all fluorescent lamps, CFLs contain a tiny amount of mercury, which is needed to make the inert gasses conductive at all temperatures and to make the lamp work properly and efficiently. Mercury can be hazardous to the environment, so it is important to recycle your used CFLs rather than throw them away.

CFLs Full Brightness and Cold Temperature: CFLs can be used for outdoor applications.   However, it is important to note that in cold weather, below 0°F, it will take 30 to 60 seconds for the bulb to reach full brightness. Optimum operating temperature is between 0°F and 100°F.

Could CFLs Work on Dimmers? - Yes! Although standard CFLs are not suitable for use with dimmer switches or other lighting controls, many CFL models are dimmable, as indicated on the package, and are and compatible with other lighting controls .

The chart below compares various type of fluorescent lighting

Fluorescent Lighting Type Efficacy
Color Rendition Index
Color Temperature
Straight tube 30–110 7000–24,000 50–90 (fair to good) 2700–6500 (warm to cold) Indoors/outdoors
Compact fluorescent lamp (CFL) 50–70 10,000 65–88 (good) 2700–6500 (warm to cold) Indoors/outdoors
Circline 40–50 12,000     Indoors

Fluorescent High Bay

Traditionally fluorescent lamps dominate the market for lighting commercial, institutional, and industrial spaces with ceilings less than 15 feet high. In recent years, however, the emergence of more intense and efficient fluorescent lamps coupled with specially designed reflecting fixtures has enabled fluorescent systems to break through the ceiling-height barrier and compete directly with High Intensity Discharge (HID) lamps in indoor applications. Most of today's fluorescent high bay fixtures use linear fluorescent lamps, either T8s or high-output T5s, because they provide longer life, higher efficacy, and less lumen depreciation than compact fluorescent lamps (CFLs) and twin-tube lamps. Better reflector designs allow fluorescent high bay lamps to be applicable at any height where an HID lamp is used. Although fluorescent high bay fixtures are available in a number of shapes, most modern fluorescent high-bay fixtures are square or rectangular.


Fluorescent High Bay Make-Over

The two pictures below shows the difference in illumination by traditional HID lamps (left) and Fluorescent High Bay (Right) in a school gym.


Twice the light, half of the energy!

The two pictures below shows the difference in illumination by traditional HID lamps (left) and Fluorescent High Bay (Right) in a printing facility. The meters show the amount of light (measured in lumens) in each setting. The wattage in each light fixture was decreased from 400 watts to 256 watts when HID was replaced with Fluorescent High Bay.


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