TechOnline

The fluorescent bulb is substantially more efficient than the incandescent alternative, producing greater direct light (and less heat) per input watt. Though long used in offices and other commercial and residential settings, fluorescent lamps didn't come in forms suitable for small-lamp replacement until the 1980s. The past couple of decades have seen miniaturized screw-in CFL bulbs finally achieve quite low price points, promoting consumer adoption.

The MaxLite bulb examined here is a 20-W lamp claimed to produce equivalent illumination to a 75-W incandescent. Like all of its traditional fluorescent peers, the MaxLite CFL uses a glass tube whose phosphor lining emits from UV radiation produced by ionized gas in the tube. The CFLs achieve miniaturization through both a smaller tube diameter and through folded or spiral-wound construction. The CFL ballast used to light the tube also must be stuffed into the space constraints of a standard screw-in lamp. To do this the MaxLite, and its competitors, use a downsized supply to create a suitable lamp drive in relatively little space.

A pair of transistors, quartet of diodes, and collection of capacitors and inductors all come together to first rectify the AC power and create a follower resonant inverter circuit that generates the high-frequency, high-voltage power used to fire the lamp. I'm no power supply expert so I may have the precise topology wrong, but both inspection of the minimal components and finished goods' price points show that the CFL ballast can be made inexpensively.

The phosphor-coated glass tube has its own evolved history in manufacturing such that the combination of lamp and electronic drive circuits can now be brought to market at prices that start to rival the (relatively) short-lived incandescent alternative. When efficiencies and lifetimes are considered, the CFL begins to look attractive not only for its "green" attributes but also for total cost of ownership.

Wearout of lamp phosphors remains an issue, and vent holes in the lamp-base enclosure suggest that heat-related wearout of ballast electronics might be a factor. Still, the lifetime of quality CFLs can run to many months or even years.