Incandescent Light Bulb Versus Compact Fluorescent Light

With the planned phase-out of incandescent light bulbs, much attention is focused on compact fluorescent lights (CFLs) which are touted as a more energy-efficient and longer lasting alternative. Here is a comparison between the two lighting technologies to help you make the transition to CFLs.

Incandescent Light Bulb

Thomas Edison invented the first commercially practical incandescent light in 1879. His design, which featured a more effective incandescent material, a higher resistance, and a higher bulb vacuum, improved upon earlier designs that dated back to the mid 1800's. An early version of Edison's bulb employed a carbonized bamboo filament that could last for over 1200 hours. The tungsten filament, still in use today, was introduced in 1906.

The modern incandescent light bulb consists of a filament of coiled tungsten wire housed inside a glass bulb. When an electric current is passed through the filament, it heats to a high temperature until it glows, thereby producing light. The bulb is filled with an inert gas, typically argon, to reduce evaporation of the tungsten filament and prevent combustion.

Incandescent light bulbs come in a range of shapes and sizes, the most familiar being the pear-shaped household bulb. Other types include candle, twisted candle, flame, globe, mushroom, and various kinds of reflector bulbs including flood, track, and recessed lights.

Compact Fluorescent Light

A compact fluorescent light (CFL) is an energy-saving fluorescent lamp designed to replace an incandescent bulb. The most common type is the helical (three-dimensional spiral) CFL, invented in 1976 by an engineer at General Electric in response to the 1973 oil crisis. Sales of helical lamps have steadily increased since large-scale manufacturing began in China in the mid 1990's.

A typical CFL consists of a tube which is curved to fit into the space of an incandescent bulb and a compact electronic ballast in the base of the lamp. When mercury vapor inside the tube is excited by an electric current, this produces ultraviolet light, which is re-radiated as visible light when it strikes fluorescent phosphors coated on the inside of the bulb. The use of an electronic rather than electromagnetic ballast eliminates most of the flickering and slow starting typically associated with fluorescent lighting.

Light Quality

An incandescent light bulb produces warmer color tones, or temperatures, than a compact fluorescent bulb. Warm color temperatures are preferred by many people in bedrooms, dining rooms, and living rooms because of the soothing atmosphere produced.

Some people complain about CFL light being harsh and unnatural but good quality CFLs provide light with a color rendering index (CRI) of 80 to 90, approaching the quality of incandescent bulbs which have a CRI of 100. Light sources with higher CRI's tend to make people and objects look better than light sources with lower CRI's.

Energy Efficiency

Only about 10% of the power consumed by an incandescent light bulb is converted into light. The remaining 90% is lost as heat. In contrast, compact fluorescent bulbs convert nearly all of the consumed power into light. A CFL uses about 75% less energy than an incandescent bulb of equivalent brightness and lasts 6 to 15 times longer. A 20-watt CFL produces the same amount of light as a 75-watt incandescent bulb.

Although the heat produced by an incandescent bulb is generally considered wasteful, it is advantageous for applications such as incubators, poultry brooding boxes, heat lights for reptile tanks, and industrial heating and drying processes.

Life Span

The lifetime of incandescent light bulbs, which is determined by evaporation of the tungsten filament, ranges from several hundred to about 2,000 hours. Common household bulbs typically have a rating of 750 or 1000 hours. Hotter filaments are more efficient but evaporate faster than cooler filaments so there is a tradeoff between bulb efficiency and longevity.

CFLs typically have a rated lifespan of 6,000 to 15,000 hours. The life of a CFL is significantly shorter if it is turned on and off frequently. It is recommended that fluorescent lamps be left on when leaving a room for less than 15 minutes to mitigate this problem.

Cost

CFL's cost more than incandescent bulbs - typically 3 to 10 times as much - but are actually more economical in the long run because of their greater lifetime and energy efficiency. According to GE, replacing a conventional 60-watt bulb with a 13-watt CFL can save a single household $30 in energy costs over the life of the bulb.

Environmental Impact

CFLs contain mercury, a toxic chemical, so they should be recycled rather than just thrown into the garbage. If a bulb breaks accidentally, there are EPA-specified clean-up steps to prevent the mercury fumes from spreading.

Other Considerations

Incandescent lights are generally a better choice than CFLs in cold areas, in fixtures subjected to shock or vibration such as garage door openers, and in fixtures that are frequently switched on and off, and in dimmers (although CFLs are making progress in this area).