Comparison with incandescent lamps

Lifespan

The average rated life of a energy saving light is between 8 and 15 times that of incandescents. Compact Fluorescent Light typically have a rated 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 with long rated lifespans of 20,000 hours have reduced light output.  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, lamp orientation and ambient operating temperature, among other factors. The life of a energy saving light 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 energy saving light 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.
Compact Fluorescent Light produce 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 first used. By the end of their lives, Compact Fluorescent Light 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, compact fluorescent lamp use between one fifth and one third 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 compact fluorescent lamp could save as much as 7% from household usage.
If incandescent lamps are replaced by compact fluorescent lamp 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. If the building requires both illumination and cooling, then compact fluorescent lamp 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.
In order to compare the actual energy efficiency of compact fluorescent lamp 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, the efficiency of the energy saving light ballast and other factors.

Cost

While the purchase price of an integrated energy saving light 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 compact fluorescent lamp 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."
compact fluorescent lamp are extremely cost-effective in commercial buildings. A energy saving light replacing a 75 W incandescent fixture offers an average yearly savings of $22 considering direct energy saving, reduced HVAC cost, and reduced labor to change lamps. 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.

Starting time

Incandescents give light almost immediately upon the application of voltage. compact fluorescent lamp take a perceptible time to achieve full brightness, and can take much longer in very cold temperatures. Certain styles of lamp using a mercury amalgam can take up to three minutes to reach full output. Coupling this with the shorter life of compact fluorescent lamp when turned on and off for short amounts of time may make incandescent bulbs more attractive for applications such as outdoor or motion-activated lighting.

Comparison with alternative technologies

Another type of fluorescent lamp is the Electrodeless lamp, known as a radiofluorescent lamp or fluorescent induction lamp. These lamps have no wire conductors penetrating their envelopes, and instead excite mercury vapor using a radio-frequency oscillator. Currently, this type of light source is struggling with a high cost of production, stability of the products produced in China, establishing an internationally recognized standard and problems with EMC and RFI. Induction lighting is excluded from Energy Star standard for 2007 by the EPA.

Some manufacturers make energy saving light bulbs with an external nano-particle coating of titanium dioxide. The manufacturer claims that the titanium dioxide when exposed to UV light produced by the energy saving light can neutralize odors and kill bacteria, viruses, and mold spores.

The Cold Cathode Fluorescent Lamp (Cenergy saving light) is one of the newest forms of energy saving light. Ccompact fluorescent lamp use electrodes without a filament. The voltage of Ccompact fluorescent lamp is about 5 times higher than compact fluorescent lamp and the current is about 10 times lower. Ccompact fluorescent lamp have a diameter of about 3 millimeters. Ccompact fluorescent lamp were initially used for backlighting LCD displays, but they are now also manufactured for use as lamps. The efficacy (lumens/watt) is about half that of compact fluorescent lamp. Their advantages are that they are instant-on, like incandescents, they are compatible with timers, photocells and dimmers, and they have a long life of approximately 50,000 hours. Ccompact fluorescent lamp are a convenient transition technology for those who are not comfortable with the short lag time associated with the initial lighting of compact fluorescent lamp. They are also an effective and efficient replacement for lighting that is turned on and off frequently with little extended use (e.g. a bathroom or closet).