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Fluorescent lamps are more efficient than incandescent light bulbs of an equivalent brightness. This is because a greater proportion of the power used is converted to usable light and a smaller proportion is converted to heat, allowing fluorescent lamps to run cooler. A typical 100 Watt tungsten filament incandescent lamp may convert only 2.6% of its power input to visible light, whereas typical fluorescent lamps convert between 6.6% and 15.2% of their power input to visible light – see the table in the luminous efficacy article. Typically a fluorescent lamp will last between 10 to 20 times as long as an equivalent incandescent lamp.
The higher initial cost of a fluorescent lamp is usually more than compensated for by lower energy consumption over its life. The longer life may also reduce lamp replacement costs, providing additional saving especially where labour is costly. Therefore it is widely used by businesses worldwide, but not so much by households.
Psychological and physiological sensitivity
Certain individuals possess a pathological sensitivity to fluorescent light. For example, some people with photo-sensitivity due to neurological conditions such as epilepsy, autism and Asperger’s syndrome may feel sick or overstimulated by the near-subconscious flickering of fluorescent tubes. People who have diseases such as lupus may experience intensification of symptoms if exposed to fluorescent lighting for long periods of time.
Fluorescent lamps require a ballast to stabilize the lamp and to provide the initial striking voltage required to start the arc discharge. This increases the cost of fluorescent luminaries, though often one ballast is shared between two or more lamps. Electromagnetic ballasts with a minor fault can produce an audible humming or buzzing noise.
Conventional lamp ballasts do not operate on direct current. If a direct current supply with a high enough voltage to strike the arc is available, a resistor can be used to ballast the lamp but this leads to low efficiency because of the power lost in the resistor. Also, the mercury tends to migrate to one end of the tube leading to only one end of the lamp producing most of the light. Because of this effect, the lamps (or the polarity of the current) must be reversed at regular intervals.
Fluorescent lamp ballasts have a power factor of less than unity. For large installations, this makes the provision of electrical power more expensive as special measures need to be taken to bring the power factor closer to unity.
Fluorescent lamps are a non-linear load and generate harmonics on the 50 Hz or 60 Hz sinusoidal waveform of electrical power supply. This can generate radio frequency noise in some cases. Suppression of generation of harmonics is standard practice, but imperfect. Very good suppression is possible, but adds to the cost of the fluorescent fixtures. The result can be interference with some radio reception bands in some cases.
Optimum operating temperature
Fluorescent lamps operate best around room temperature (say, 20 Â°C or 68 Â°F). At much lower or higher temperatures, efficiency decreases and at low temperatures (below freezing) standard lamps may not start. Special lamps may be needed for reliable service outdoors in cold weather. A “cold start” electrical circuit was also developed in the mid-1970s.
Non-compact light source
Because the arc is quite long relative to higher-pressure discharge lamps, the amount of light emitted per unit of surface of the lamps is low, so tube lamps were large compared with incandescent sources. However, in many cases low luminous intensity of the emitting surface was useful because it reduced glare. The bulk created by this lamp affected the design of fixtures since light must be directed from long tubes instead of a compact source. Recently, a new type of fluorescent lamp, the CFL has been introduced to address this issue and allow regular incandescent sockets to be fitted with this type of lamp, thereby negating the need to mount it on special fixtures.
Fluorescent fittings using a magnetic mains frequency ballast do not give out a steady light; instead, they flicker (fluctuate in intensity) at twice the supply frequency. While this is not easily discernible by the human eye, it can cause a strobe effect posing a safety hazard in a workshop for example, where something spinning at just the right speed may appear stationary if illuminated solely by a fluorescent lamp. It also causes problems for video recording as there can be a ‘beat effect’ between the periodic reading of a camera’s sensor and the fluctuations in intensity of the fluorescent lamp.
Incandescent lamps, due to the thermal inertia of their element, fluctuate to a lesser extent. This is also less of a problem with compact fluorescents, since they multiply the line frequency to levels that are not visible. Installations can reduce the stroboscope effect by using lead-lag ballasts, by operating the lamps on different phases of a polyphase power supply, or by use of electronic ballasts.
Electronic ballasts do not produce light flicker, since the phosphor persistence is longer than a half cycle of the higher operation frequency.
The issues with color faithfulness of some tube types are discussed above.
Unless specifically designed and approved to accommodate dimming, most fluorescent light fixtures cannot be connected to a standard dimmer switch used for incandescent lamps. Two effects are responsible for this: the waveshape of the voltage emitted by a standard phase-control dimmer interacts badly with many ballasts and it becomes difficult to sustain an arc in the fluorescent tube at low power levels. Many installations require 4-pin fluorescent lamps and compatible controllers for successful fluorescent dimming; these systems tend to keep the cathodes of the fluorescent tube fully heated even as the arc current is reduced, promoting easy thermionic emission of electrons into the arc stream.
Disposal and recycling
The disposal of phosphor and particularly the mercury in the tubes is an environmental issue. (Incandescent lamps do not contain mercury.)
For large commercial or industrial users of fluorescent lights, recycling services are available in many nations, and may be required by regulation. In some areas, recycling is also available to consumers. The need for a recycling infrastructure is an issue with instituting proposed bans of incandescent bulbs.