CF bulbs came about as a means to put energy efficient fluorescent bulbs where they could not be used before because of the awkwardly huge size of the bulbs. The total lumens depends upon the tube length and the tube diameter.
In a CF, the tubes are bent into a tight pattern to reduce the overall length of the bulb. Most CF bulbs have a ballast built into the base, so they can act as a direct replacement for incandescent bulbs. Unfortunately, buying a new ballast with each bulb drives up the price. A 23 Watt CF bulb may cost 30 times as much as the 100 Watt incandescent bulb it replaces.
Non-Ballasted CF Bulbs
Some CF bulbs have the bulb sold separately from the ballast. Most of those have the ballast permanently mounted to the lamp assembly, and the shape of the bulb-to-ballast interface may be proprietary. That means if the bulb ever becomes unavailable, you will have to replace the entire lamp assembly. Plus, you can't take advantage of new technologies that come along.
Since CF bulbs are far more efficient than incandescent bulbs, you need to read the packaging and look at the lumen output. Most CF manufacturers list the equivalent incandescent wattage. A 23 watt CF can produce as much light as a 90 watt incandescent. The energy savings is obvious. CF bulbs also have the long 10,000+ hour life of their full-length cousins.
Differences Between CF and Incandescent Bulbs
One difference between incandescent bulbs and CF bulbs takes a bit of getting used to: CF bulbs are not instant-on. There is about a half-second delay. It is a small delay, but if you hit the light switch expecting instant light, the delay can be unsettling. Also, CF bulbs take a few minutes to reach maximum brightness.
Two factors set apart good CF bulbs from lesser ones. First is color. Many inexpensive CF bulbs have terrible color. If you are unsure about the color, buy the bulb at a store that will let you return it if you don't like it. Philips has done extensive development in their phosphors, and the color from their fluorescent bulbs is the best I've ever seen. I have used two Philips CF bulbs in my living room lamps for many years.
The second factor is outdoor use. CF bulbs face the same temperature limitations as their full-length cousins. A very notable exception is some of Philips's Marathon and Earth Light CF bulbs. Some of them are packaged as being for outdoor use. How is that possible? Chemistry! Philips uses clever mercury alloy. The alloy's chemistry controls the level of mercury vapor in the bulb, thus the light output is controlled over...