By A-line light bulb, I assume you are referring to a legacy style incandescent bulb running off of 120VAC in the U.S., and similar 240VAC versions other places. I have built a 120 VAC led bulb in the past, but did not have good results with it. I wired about 44 LED's in series with a resistance in series to limit current from a rectified 120VAC source. This is not a good way to go. First, with the exception of the latest LED's out there, it is less efficient than a comparable flourescent, say a circle line 22 Watt, or even a compact flourescent. Second, when LED's fail, they can fail to short which can increase current through the remaining LED's in a string. The more LED's in series, the more likely this is to be a problem. I think only one of five strings survived about a year of operation in the one I built.
If I were to build one now, I would look for the most efficient switching power supply to bring the mains voltage down to a voltage suitable to drive 1 to 3 LED's that would fit in the package that I was trying to put together. Then I would either use a dedicated LED driver chip to power a string of 3 LED's or build one of Commanda's LED driver circuits that use a FET as a variable resistance element. You can read about my endeavors with Amanda's Circuit here, which also has links back to her set of posts on the subject:
http://www.fieldlines.com/story/2007/10/12/182256/43
My prototype has thus far proven to be reliable and reasonably efficient. It may be possible to get an off the shelf switching power supply that limits the current out which would further increase efficiency and eliminate the need for a separate driver circuit for one string of LED's or a small equalizing resistor for multiple strings.
Rich
