An energy-saving light bulb uses approximately 1/4 of the energy consumed by an incandescent bulb to produce the same light output. For example, a 15-watt compact fluorescent bulb (CFL) emits the same light as a 60-watt incandescent bulb.
Some CFL products are even more efficient, needing only three to 13 watts to generate bright light.
An incandescent light bulb works by running a current through a filament in a glass enclosure filled with argon gas. A great deal of heat is needed to create light this way.
Incandescent bulbs use 90 percent of their electricity to generate this heat. In contrast, energy-saving CFL bulbs work when moving electrons collide with trace amounts of mercury, creating ultraviolet light that triggers a phosphor coating inside the bulb.
Light is produced with very little heat, making a CFL 75 percent more efficient than an incandescent bulb.
The price of energy-savings light bulbs sometimes deters people from buying them, as on average the cost of a single CFL bulb is $350, compared to 50 cents for a traditional 60-watt bulb. Nonetheless, the lower wattage and longer life span of a CFL actually saves money over time.
A single CFL bulb costs about $120 a year to operate, while a standard bulb costs about $480. According to an energy cost calculator, using a CFL bulb saves you approximately $42 during its lifetime.
(see Reference 1).
An energy-saving light bulb radiates a different light spectrum that may be unappealing for some. Incandescent light is warmer and softer, while fluorescent light might seem harsh or dim.
CFL bulbs also may take a while to reach to their full light output, while incandescent bulbs are at full strength instantaneously. However, higher quality CFLs have improved their light output and appeal by developing better phosphor formulations, resulting in warmer, softer light.
The average life span of an incandescent bulb is 750 to 1,000 hours, while energy-saving light bulbs last at least 10 times longer---on average eight to 10 years, or 10,000 hours. LED light bulbs, which are making their way to the market, last even longer, with an average lifetime of 50,000 hours.
In its lifetime, a single CFL light bulb helps reduce greenhouse gases by eliminating 691 pounds of carbon dioxide that would have been produced to create an incandescent light bulb. However, CFL bulbs contain small amounts of mercury, a toxic substance that must be carefully disposed of to avoid contamination.
Aside from that, the US. government's Energy Star program claims that using CFL bulbs actually results in less mercury being released into the environment, as coal-fired plants use 136 milligrams of mercury to produce a 60-watt incandescent bulb and 33 milligrams for a CFL bulb.
So although a CFL bulb contains approximately 4 milligrams of mercury, using one instead of one incandescent bulb results in 53 fewer milligrams of mercury being released into the environment. (see Reference 3).