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Compared to general service incandescent lamps giving the same amount of visible light, CFLs use less power and have a longer rated life. In the United States, a CFL can save over 30 USD in electricity costs over the lamp's lifetime compared to an incandescent lamp and save 2000 times its own weight in greenhouse gases. The purchase price of a CFL is higher than that of an incandescent lamp of the same luminous output, but this cost is recovered in energy savings and replacement costs over the bulb's lifetime. Like all fluorescent lamps, CFLs contain mercury; this complicates the disposal of fluorescent lamps and causes a health risk when they are broken.
CFLs radiate a different light spectrum from that of incandescent lamps. Improved phosphor formulations have improved the subjective color of the light emitted by CFLs such that the best 'soft white' CFLs available in 2007 are subjectively similar in color to standard incandescent lamps.
History of CFL
The parent to the modern compact fluorescent lamp (CFL) was invented in the late 1890s by Peter Cooper Hewitt.The Cooper Hewitt lamps were used for photographic studios and industries. Edmund Germer, Friedrich Meyer, and Hans Spanner then patented a high pressure vapor lamp in 1927. George Inman later teamed with General Electric to create a practical fluorescent lamp, sold in 1938 and patented in 1941. The modern CFL was invented by Ed Hammer, an engineer with General Electric, in response to the 1973 oil crisis. While it met its design goals, it would have cost GE about 25 million USD to build new factories to produce them and the invention was shelved. The design was eventually leaked out and copied by others.
Market of Energy Saving Lamp
A compact fluorescent lamp used outside an office complex.Globally introduced in the early 1980s, CFLs have steadily increased in sales volume. The most important advance in fluorescent lamp technology (including CFLs) has been the gradual replacement of magnetic ballasts with electronic ballasts; this has removed most of the flickering and slow starting traditionally associated with fluorescent lighting. There are two types of CFLs: integrated and non-integrated lamps.
Integrated lamps combine a tube, an electronic ballast and either an Edison screw or bayonet fitting in a single CFL unit. These lamps allow consumers to easily replace incandescent lamps with CFLs. Integrated CFLs work well in standard incandescent light fixtures. This lowers the cost of CFL use, since they can reuse the existing infrastructure. In addition, incandescent light fixtures are relatively inexpensive.
Non-integrated lamps allow for the replacement of consumable bulbs and the extended use of electrical ballasts in a light fixture. This fluorescent bulb itself does not include a ballast. Since the ballasts are placed in the light fixture they are larger and last longer, vis-a-vis the integrated ones. Non-integrated CFL housings can be both more expensive and sophisticated, providing options such as dimming, less flicker, faster starts, etc.
The ballasts make these light fixtures relatively expensive. They cost anywhere from 85 to 200 USD for each recessed can. If a ballast with dimming capabilities is desired the cost is anywhere from 125 to 300 USD per recessed can. Non-integrated CFLs are more popular for professional users, such as hotels and office buildings. The more advanced capabilities of these sophisticated external ballasts (e.g., faster starts, limited flicker, dimming, longer lifespans, etc.) are starting to appear in integrated CFLs.
Another style of non-integrated fitting is the "two piece", where the initial system includes a base adapter and detachable fluorescent tube module, and subsequently only the tube unit is replaced. The Thorn 2D and some Philips PL versions are examples, but while replacement tubes are generally still available, it is rare to see the complete kit on sale, having been overshadowed by cut-price one-piece units.
CFL power sources
CFLs are produced for both alternating current (AC) and direct current (DC) input. DC CFLs are popular for use in recreational vehicles and off-the-grid housing. Some families in developing countries are using DC CFLs (with car batteries and small solar panels) and/or wind generators, to replace kerosene lanterns.
CFLs can also be operated with solar powered street lights, using solar panels located on the top or sides of a pole and luminaires that are specially wired to use the lamps.
Lifespan of Energy Saving LightsModern CFLs typically have a lifespan of between 6,000 and 15,000 hours, whereas incandescent lamps are usually manufactured to have a lifespan of 750 hours or 1,000 hours. These lifetimes are quoted according to IEC60969, which specifies that "life to 50% of failures shall be not less than value declared by the manufacturer". Some incandescent bulbs claim long rated lifespans of 20,000 hours with reduced light output (approximately 500 versus 800 lumens). The lifetime of any lamp depends on many factors including operating voltage, manufacturing defects, exposure to voltage spikes, mechanical shock, frequency of cycling on and off and ambient operating temperature, among other factors. The life of a CFL is significantly shorter if it is only turned on for a few minutes at a time: In the case of a 5-minute on/off cycle the lifespan of a CFL can be up to 85% shorter, reducing its lifespan to the level of an incandescent lamp. The US Energy Star program says to leave them on at least 15 minutes at a time to mitigate this problem.
CFLs give less light later in their life than they do at the start. The light output depreciation is exponential, with the fastest losses being soon after the lamp was new. By the middle to end of their lives, CFLs can be expected to produce 70-80% of their original light output. (An Incandescent lamp which gives 93% or less of its initial light output at 75% of its rated life is regarded as unsatisfactory, when tested according to IEC Publication 60064. Light loss is due to filament evaporation and bulb blackening. ) The response of the human eye to light is logarithmic: Each f-number (or photographic 'f-stop') reduction represents a halving in actual light, but is subjectively quite a small change. A 20-30% reduction over many thousands of hours represents a change of about half an f-stop, which is barely noticeable in everyday life.
Energy efficiency of CFL LampsThe chart shows the energy usage for different types of light bulbs operating at different light outputs. Points lower on the graph correspond to lower energy use.For a given light output, CFLs use between one fifth and one quarter of the power of an equivalent incandescent lamp. For example, lighting accounted for approximately 9% of household electricity usage in the United States in 2001, so widespread use of CFLs could save most of this, for a total energy saving of about 7% from household usage.
If incandescent lamps are replaced by CFLs the heat produced by the building's lighting system will be reduced. At times when the building requires both heating and lighting, the building's central heating system will then supply the heat. Depending on the fuel used for heating and for electricity production, this may result in either a small increase or a small decrease in the total cost and environmental impact of changing to CFLs.
In contrast, if the building requires both illumination and cooling, then CFLs will use less electricity themselves and will also reduce the load on the cooling system compared to incandescent lamps. This results in two concurrent savings, and since most air conditioners are also electrically powered, they are directly comparable.
There is a third case where electric lighting is used with natural ventilation and without either heating or cooling. In this case the energy savings due to CFLs are simpler to estimate, as described above.
For more details on this topic, see Luminous efficacy. In order to compare the actual energy efficiency of CFLs with various other lamp technologies such as incandescent, LED and halogen, factors to compare include total lumens, the usefulness of different frequencies of light, the distribution of light around the lamps and other factors.
CFL CostIn addition to the above savings on energy costs, the average life of a CFL is between 8 and 15 times that of incandescents. While the purchase price of a CFL is typically 3 to 10 times greater than that of an equivalent incandescent lamp, the extended lifetime (fewer lamps to replace and reduced labor) and lower energy use will compensate for the higher initial cost in many applications. A US article stated "A household that invested $90 in changing 30 fixtures to CFLs would save $440 to $1,500 over the five-year life of the bulbs, depending on your cost of electricity. Look at your utility bill and imagine a 12% discount to estimate the savings."
Cost-Effectiveness in Commercial Buildings
CFLs are extremely cost-effective in commercial buildings. A CFL replacing a 75 W incandescent fixture offers an average yearly savings of $22 when the impact of replacing incancesdents HVAC systems and other operating expenses are accounted for. The capital investment of $2 per fixture is typically paid back in about one month. Savings are greater and payback periods shorter in regions with higher than average electric rates and, to a lesser extent, higher than average cooling requirements.
CFLs, much as other fluorescent lights, may emit a high-pitched buzzing sound, where incandescents do not. Such sounds are particularly noticeable in quiet rooms, and can be annoying under these circumstances. Newer compact fluorescent light bulbs are nearly noiseless, but some poorly made CFLs may still emit an audible buzz.
As with all fluorescent lights, CFLs also generate some higher electrical frequencies which both radiate from the light unit itself, and transfer along the interconnecting electrical wiring. This is not generally considered to be a significant problem, but it can result in electronic interference with some other devices.
Comparison with alternative technologiesSolid-state lighting has already filled a few specialist niches such as traffic lights and may have the potential to compete with CFLs in the near future. LED lamps have current efficiencies of 30% with higher levels attainable (recently up to 85 lm/w LEDs are available), and a lifetime of around 50,000 hours. Currently LED lamps do not deliver the intensity of light output for domestic uses at a reasonable cost.
General Electric is attempting to develop more efficient incandescent bulbs that can produce the same light output as a 60-watt bulb (~800 lumens) but with half the wattage (30 watt). Their ultimate goal is to manufacture an incandescent bulb that will match the CFL's performance (a 15 watt bulb outputting 60-watt equivalency).
Color temperature is a quantitative measure. The higher the number in kelvins, the 'cooler', i.e., bluer, the shade. Color names associated with a particular color temperature are not standardized for modern CFLs and other triphosphor lamps like they were for the older-style halophosphate fluorescent lamps. Variations and inconsistencies exist among manufacturers. For example, Sylvania's Daylight CFLs have a color temperature of 3500 K, while most other lamps with a 'daylight' label have color temperatures of at least 5000 K. Some vendors do not include the kelvin value on the package, but this is beginning to change now that the Energy Star Criteria for CFLs is expected to require such labeling in its 4.0 revision.
Some manufacturers now label their CFLs with a 3 digit code to specify the color rendering index (CRI) and color temperature of the lamp. The first digit represents the CRI measured in tens of percent, while the second two digits represent the color temperature measured in hundreds of Kelvins. For example, a CFL with a CRI of 82% and a color temperature of 2700K would be given a code of 827.
CFLs are also produced, less commonly, in other colors:
Red, green, orange, blue, and pink, primarily for novelty purposes Blue for phototherapy Yellow, for outdoor lighting, because it does not attract insects Black light (UV light) for special effects Black light CFLs, those with UVA generating phosphor, are much more efficient than incandescent black light lamps, since the amount of UV light that the filament of the incandescent lamp produces is only a fraction of the generated spectrum.
Being a gas discharge lamp, a CFL will not generate all frequencies of visible light; the actual color rendering index is a design compromise (see below). With less than perfect color rendering, CFLs can be unsatisfactory for inside lighting, but modern, high quality designs are proving acceptable for home use.
Other terms that apply to CFLs: Full Spectrum High Definition