Compact Fluorescent Lamp (CFL) – Working Principle, Types, Advantages and Disadvantages:

A compact fluorescent lamp (CFL), also known as a compact fluorescent light or energy saving light, is a type of fluorescent lamp which combines the energy efficiency of fluorescent lighting with the convenience and popularity of incandescent fixtures. CFLs can replace incandescents that are roughly 3-4 times their wattage, saving up to 75% of the initial light energy. Although CFLs costs 3-10 times more than comparable incandescent lamps. they last about 10 times as long (10,000 hours).

CFLs are most cost effective in areas where lights are ON for long periods of time.

Because of the potential of reducing electric consumption and pollution, some organizations have encouraged the adoption of CFLs. Some electric utilities and local governments have subsidized CFLs as a means of reducing electric demand. In India also almost all the states are encouraging the adoption of CFLs in place of incandescent lamps and are providing incentives or even distributing CFLs to people free of cost to save electricity.

CFLs radiate a light spectrum different from that of incandescent lamps. Improved phosphor formulations have improved the perceived colour of the light emitted by CFLs such that some sources rate the best “soft white” CFLs as subjectively similar in colour to standard incandescent lamps.

Like all fluorescent lamps, CFLs contain mercury, which makes their disposal complicated.

Working Principle:

CFLs work much like standard fluorescent lamps. They consist of two components : a gas-filled tube, and a magnetic or electronic ballast. The gas in the tube glows with ultraviolet light when switched ON and electric current 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 tube surface.

CFLs with magnetic ballasts flicker slightly at start. They are also heavier than those with electronic ballasts. This may make them too heavy for some light fixtures. Electronic ballasts are more expensive, but light immediately (especially at low temperature). They are also more efficient than magnetic ballasts. The tubes will last about 10,000 hours and the ballast about 50,000 hours. Most currently available CFLs have electronic ballasts.

Electronic ballasts contain a small circuit board with rectifiers, a filter capacitor and usually two switching transistors connected as a high-frequency resonant series dc to ac inverter. The resulting high frequency (about 40 kHz or higher) is applied to the lamp tube. Since the resonant converter tends to stabilize lamp current and so the light produced over a range of input voltages, standard CFLs do not respond well in dimming applications and special lamps are required for dimming services.

CFLs are designed to operate within a specified temperature range. Temepratures below the range cause reduced output. Most of the CFLs are for indoor use, but there are models available for outdoor use. Outdoor CFLs need installation in enclosed fixtures so as to minimize the adverse effects of low temperatures.

Types of CFLs: CFLs are available in a variety of styles or shapes. Some have two, four, or six tubes while others have circular or spiral-shaped tubes. The size or total surface area of the tube(s) determines how much light it produces.

Some CFLs have the tubes and ballast permanently connected. Other CFLs have separate tubes and ballasts which facilitates in replacement of tubes without changing the ballast. They are also of types enclosed in a glass tube. These look somewhat similar to conventional incandescent lamps, except they are larger.

Types of Compact Fluorescent Lamp (CFL):

CFLs are of two types, namely

1. integrated and
2. non-integrated lamps.

Integrated lamps combine a tube, an electronic ballast and either an Edison screw or a bayonet in a single unit. The incandescent lamps can be easily replaced with CFLs. Integrated CFLs work well in many standard incandescent light fixtures, reducing the cost of conversion.

Non-integrated CFLs have the ballast permanently installed in the luminaire, and only lamp is usually replaced at the end of life. Since the ballasts are placed in the light fixture, they are larger and last longer in comparison to the integrated ones. Non-­integrated Compact Fluorescent Lamp housings can be both more expensive and sophisticated. They have two types of tubes : bi-pin tubes and quad-pin tubes. Bi-pin tubes are designed for conventional ballasts, and quad-pin tubes are designed for electronic ballasts or conventional ballasts with external starters. A bi-pin tube contains an integrated starter which obviates the need for external heating pins but causes incompatibility with electronic ballasts.

CFLs are produced for operation on both dc and ac supply. DC CFLs are popular for use in recreational vehicles and off­-the-grid housing. CFLs can also be operated with solar powered street lights, using solar panels located on the top or sides of a pole and light fixtures that are specially wired to use the lamps.

Advantages of CFLs Over Incandescent Lamps:

1. Life Span: As already mentioned, the average rated life of a Compact Fluorescent Lamp is about 10 times that of incandescent lamps.

The lifetime of any lamp depends on various factors, such as operating voltage, exposure to voltage spikes, mechanical shock, frequency of cycling on and off, lamp orientation, ambient temperature, manufacturing quality etc. The life of a Compact Fluorescent Lamp is significantly reduced if it is turned on and off frequently. In the case of a 5 minute on/off cycle the life span of a Compact Fluorescent Lamp can be reduced to “close to that of incandescent lamp”.

CFLs provide less light in their lives than when they are new. The light output decay is exponential, with the fastest losses being soon after the lamp is first used. By the end of their lives, they can be expected to produce 70-80% of their original light output.

2. Energy Efficiency: For a given light output, CFLs consume 20 to 33 per cent of the power of equivalent incandescent lamps. Electrical power equivalents for different lamps are indicated below.

3. Heating and Cooling: If in a building, indoor incandescent lamps are replaced by CFLs, the heat produced due to lighting will be significantly reduced. In warm climates office/industrial buildings where air-conditioning is usually required, CFLs would reduce the load on the cooling system resulting in saving in electrical consumption, in addition to the energy efficiency savings of using CFLs instead of incandescent lamps. However, in cooler climates in which buildings need heating, the heating system would need more electrical energy. While the CFLs are still saving electricity, total greenhouse gas emissions may increase in certain scenarios, such as the operation of natural gas furnace to replace unintended heating from CFLs running on low-GHG electricity. Thus overall energy cost saving depends on the climate, increased heating demand offsets some of the lighting energy saved.

4. Efficiency: The typical luminous efficiency of CFLs is 60 to 72 lumens/watt, and that of normal domestic incandescent lamps is 13 to 18 lumens/watt. Compared to a theoretical 100% efficient lamp, these figures are equivalent to lighting efficiency ranges of 9 to 11% for CFLs (60/680 to 72/680), and 1.9 to 2.6% for incandescent (13/680 to 18/680).

5. Embodied Energy: No doubt, CFLs need more energy in manufacturing than the incandescent lamp but this embodied energy is offset by their longer life and small energy consumption than equivalent incandescent lamps.

6. Cost: While the purchase price of an integrated Compact Fluorescent Lamp is typically 3 to 10 times higher than that of an equivalent incandescent lamp, the extended lifetime and lower energy consumption will more than compensate for the higher initial cost. CFLs are extremely cost-effective in commercial buildings when used to replace incandescent lamps.

7. Starting Time: Incandescent lamps attain full brilliancy a fraction of second after being switched on, CFLs turn on within a second, but many still take time to warm up to full brightness. The light colour may be slightly different immediately after being switched on. Some CFLs are marketed as “instant on” and have no noticeable warm-up period, but others can take up to a minute to attain full brightness, or longer in very cold temperatures. Some that make use of a mercury amalgam can take up to three minutes to attain full brightness. This and shorter life of CFLs when turned on and off for short periods may make CFLs less suitable for applications like motion-activated lighting.

Disadvantages of Compact Fluorescent Lamp (CFL):

1. Health Issues: If individuals are exposed to the light produced by some single-envelope CFLs for long periods of time at distances of less than 20 cm, it could lead to ultraviolet exposures approaching the current workplace limit set to protect workers from skin and retinal damage. The ultraviolet radiation received from CFLs is too small to contribute to skin cancer and the use of double-envelope CFL lamps “largely or entirely” mitigates any other risks.

2. Environmental Issues: CFLs, like all fluorescent lamps, contain small amounts of mercury as vapour inside the glass tubing. Because mercury is poisonous, even these small amounts are a concern for landfills and waste incinerators where the mercury from lamps may be released and contribute to air and water pollution. Health and environmental concerns about mercury have promoted many jursdictions to require used lamps to be properly disposed or recycled rather than being included in the general waste stream sent to land fills. So disposal of used CFLs required proper care.