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Comparison With Incandescent Lamps

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Lifespan

Modern CFLs typically have a life span of between 6,000 and 15,000 hours (though total light output generally drops during long term use), whereas incandescent lamps are usually manufactured to have a life span of 750 hours or 1000 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.” Special-purpose incandescent lamps used for projectors and photographic lighting have shorter lifespans. The lifetime of any lamp depends on many factors including manufacturing defects, exposure to voltage spikes, mechanical shock, frequency of cycling on and off and ambient operating temperature, among other factors.

Energy Consumption

For a given light output, CFLs use between one-fifth and one-quarter of the power of an equivalent incandescent lamp, thereby saving significant amounts of energy in use and reducing the need for electrical generation. However, the energy required to manufacture these lamps is higher than incandescent lamps, and as a result the total lifetime energy use (from manufacture to disposal) compared to other forms of lighting is less than the simple comparison of electricity consumption implies. For industrialized countries, lighting makes up about one fifth of electricity consumption, so there are potentially significant benefits.

Incandescent lamps are less efficient than CFLs because incandescent lamps convert approximately 90% of the energy they consume into heat (compared to 30% for a CFL). Lighting accounted for approximately 9% of household electricity usage in the United States in 2001. If widespread use of CFLs could save three-quarters to four-fifths of this, it would amount to a total energy saving of about 7% from household usage.

Energy Efficiency

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

Cost

In addition to the above savings on energy costs, CFLs’ average life 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 and lower energy use will compensate for the higher initial cost in many applications. CFLs will fail prematurely if overheated and are not suitable for enclosed or non ventilated light fixtures, including most recessed lighting fixtures. Adapting fixtures or installing new ones for CFLs will raise the initial installation cost when required.