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Compact fluorescent lamp

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A spiral-type compact fluorescent lamp. This style has slightly reduced efficiency compared to tubular fluorescent lamps, due to the excessively thick layer of phosphor on the lower side of the twist. Despite this, it has become one of the most popular types among North American consumers since its introduction in the mid 1990s.[1]

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 standard incandescent lamps of the same luminous flux, 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 their own weight in greenhouse gases.[2] 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.[3]

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.[4]

Contents

History

The parent to the modern compact fluorescent lamp (CFL) was invented in the late 1890s by Peter Cooper Hewitt.[5] The Cooper Hewitt lamps were used for photographic studios and industries.[5] Edmund Germer, Friedrich Meyer, and Hans Spanner then patented a high pressure vapor lamp in 1927.[5] George Inman later teamed with General Electric to create a practical fluorescent lamp, sold in 1938 and patented in 1941.[5] 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.[6] The design was eventually leaked out and copied by others.[6]

Market

Image:CFL-wild-large.jpg
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 CFLs

Integrated lamps combine a tube, an electronic ballast and either a 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 CFLs

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.[7][8]

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 flourescent 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.

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.[9] These lifetimes are quoted according to IEC60969,[10] 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 [11] with reduced light output (approximately 500 versus 800 lumens). [12] 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.[13][14][15] 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 did 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. [16] (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. [17]) 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.[18] 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.[19]

Energy consumption

Image:Electricity use by lightbulb type.svg
The 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.[20] For example, lighting accounted for approximately 9% of household electricity usage in the United States in 2001,[21] so widespread use of CFLs could save most of this, for a total energy saving of about 7% from household usage.

Interaction with other energy sources

All operating electrical lamps contribute heat to a building and therefore, when considering the energy savings of CFLs versus incandescent lamps, it is necessary to consider energy used for illumination as well as energy used for heating or cooling.

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.

Energy efficiency

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 lumens, the subjective usefulness of different frequencies of light, the distribution of light over imaginary 360° spheres around the lamps and other factors. In round figures, typical incandescent lamps are around 2% efficient and domestic CFLs are currently 7%-8% efficient (life cycle comparisons are necessarily more complex).

Cost

In addition to the above savings on energy costs, the average life of a CFL is between 8 and 15 times that of incandescents.[22] 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.[23] 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."[24]

Cost-Effectiveness in Commercial Buildings

CFLs are extremely cost-effective across commercial building types and applications, on average offering undiscounted net savings of about $22 per fixture per year for replacement of a 75W incandescent, with an incremental initial capital investment of about $2 per fixture and a payback period of 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. [4]

Noise

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.

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.

Cold weather function

Incandescents give light almost immediately upon the application of voltage. CFLs take a moment to brighten up, and can take much longer in very cold temperatures. Coupling this with the shorter life of CFLs when turned on and off for short amounts of time may make incandescent bulbs more attractive for things like outdoor and/or motion-activated lighting.

Cleanup of broken bulbs

Broken fluorescent lamps inside a house or an office do pose an environmental hazard beyond that of broken glass, especially to infants, young children, and expectant mothers. Like other fluorescent lamps, broken CFLs release mercury vapors, and require special handling to clean up. The EPA warns against vacuuming, suggesting instead that individuals vacate the room and open windows for fifteen minutes to allow any mercury vapor to air out, then clean up the breakage while wearing protective gloves, and use double plastic bags for all broken pieces. They also suggest using duct tape to pick up small pieces.[3] Special handling upon breakage is currently not printed on the packaging of household CFL bulbs in many countries.[citation needed] It is important to note that the amount of mercury released by one bulb exceeds even the most lenient state level for acute exposure.[25] [26]

Comparison with alternative technologies

Solid-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.[27][28][29]

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). [30] [5]

CFL availability

Standard/Integrated CFLs

The US Environmental Protection Agency (EPA) and the US Department of Energy (DOE) run the Energy Star program, which evaluates the energy efficiency of electrical components, including integrated CFLs. Those CFLs with a recent Energy Star certification start in less than one second and do not flicker. There is ongoing work in improving the 'quality' (color-rendering index) of their light.

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