A compact fluorescent lamp (CFL), also known as a compact fluorescent light bulb (or less commonly as a compact fluorescent tube [CFT]) is a type of fluorescent lamp. Many CFLs are designed to replace an incandescent lamp and can fit in the existing light fixtures formerly used for incandescents.
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.
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.
Comparison with incandescent lamps
Lifespan:
Modern 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. 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.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:
For a given light output, CFLs use between one fifth and one quarter of the power of an equivalent incandescent lamp.Since lighting accounted for approximately 9% of household electricity usage in the United States in 2001,widespread use of CFLs could save as much as 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.
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.
Radio Frequency:
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.
How they work:
There are two main parts in a CFL: the gas-filled tube (also called bulb or burner) and the magnetic or electronic ballast. Electrical energy in the form of an electrical current from the ballast flows through the gas, causing it to emit ultraviolet light. The ultraviolet light then excites a white phosphor coating on the inside of the tube. This coating emits visible light. CFLs that flicker when they start have magnetic ballasts; CFLs with electronic ballasts are now much more common.
Electronic ballasts contain a small circuit board with rectifers, a filter capacitor and usually two switching transistors connected as a high-frequency resonant series DC to AC inverter. The resulting high frequency, around 40 kHz or higher, is applied to the lamp tube. Since the resonant converter tends to stabilize lamp current (and light produced) over a range of input voltages, standard CFLs do not respond well in dimming applications and special lamps are required for dimming service.
Energy savings:
Since CFLs use less power to supply the same amount of light as an incandescent lamp of the same lumen rating, they can be used to decrease energy consumption at the location in which they are used. In countries where electricity is largely produced from burning fossil fuels, the savings reduces emissions of greenhouse gases and other pollutants; in other countries the reduction may help reduce negative impacts from radioactive waste, hydroelectric plants, or other sources; see environmental concerns with electricity generation for details.
While CFLs require more energy in manufacturing than incandescent lamps, this is said to be offset by the fact that they last longer and use less energy during their lifespan. However there is no standard way to calculate the amount of energy 'embodied' in a device (e.g. Should one include the energy consumption/transport of workers in the factory?), and currently there is little in the way of trustworthy evidence to demonstrate the differences between the manufacturing, delivery, and retailing consumption of energy in the different forms of lighting.
A comparison of energy consumption and carbon dioxide production, also needs to specify whether this is in hot, medium or cold climates. The 'inefficiencies' of incandescent lightbulbs in cold countries are virtually zero, since the generated heat offsets some of the need for central heating.
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.
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.
Comparison with incandescent lamps
Lifespan:
Modern 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. 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.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:
For a given light output, CFLs use between one fifth and one quarter of the power of an equivalent incandescent lamp.Since lighting accounted for approximately 9% of household electricity usage in the United States in 2001,widespread use of CFLs could save as much as 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.
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.
Radio Frequency:
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.
How they work:
There are two main parts in a CFL: the gas-filled tube (also called bulb or burner) and the magnetic or electronic ballast. Electrical energy in the form of an electrical current from the ballast flows through the gas, causing it to emit ultraviolet light. The ultraviolet light then excites a white phosphor coating on the inside of the tube. This coating emits visible light. CFLs that flicker when they start have magnetic ballasts; CFLs with electronic ballasts are now much more common.
Electronic ballasts contain a small circuit board with rectifers, a filter capacitor and usually two switching transistors connected as a high-frequency resonant series DC to AC inverter. The resulting high frequency, around 40 kHz or higher, is applied to the lamp tube. Since the resonant converter tends to stabilize lamp current (and light produced) over a range of input voltages, standard CFLs do not respond well in dimming applications and special lamps are required for dimming service.
Energy savings:
Since CFLs use less power to supply the same amount of light as an incandescent lamp of the same lumen rating, they can be used to decrease energy consumption at the location in which they are used. In countries where electricity is largely produced from burning fossil fuels, the savings reduces emissions of greenhouse gases and other pollutants; in other countries the reduction may help reduce negative impacts from radioactive waste, hydroelectric plants, or other sources; see environmental concerns with electricity generation for details.
While CFLs require more energy in manufacturing than incandescent lamps, this is said to be offset by the fact that they last longer and use less energy during their lifespan. However there is no standard way to calculate the amount of energy 'embodied' in a device (e.g. Should one include the energy consumption/transport of workers in the factory?), and currently there is little in the way of trustworthy evidence to demonstrate the differences between the manufacturing, delivery, and retailing consumption of energy in the different forms of lighting.
A comparison of energy consumption and carbon dioxide production, also needs to specify whether this is in hot, medium or cold climates. The 'inefficiencies' of incandescent lightbulbs in cold countries are virtually zero, since the generated heat offsets some of the need for central heating.
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