In article 4, Wayne
Boatwright wrote in part:

Another option I've used in very old lighting with two bulbs is wiring them
in series. The bulbs last forever and the color and intensity is just
right. I have one fixture that remains on constantly, that the bulbs are
probably 30 years old or older.

As an aside, it's been said that Edison's home in Florida that is wired
with DC power still has the working original bulbs throughout.

Just keep in mind that such century-life incandescents have energy
efficiency so low that in order to produce a given amount of light, you
increase your electric bill more than you decrease your lightbulb
replacement costs.

The first-mass-marketed carbon filament incandescents had energy
efficiency of a couple to at most a few lumens per watt.

There is a "centennial bulb" with a webcam showing a publicly accessable
view of it continuing to work. I give low odds of its energy efficiency
exceeding that of a 230 volt incandescent being powered by 120 volts, or
roughly 1/4-1/3 that of modern 60-100 watt 750-1000 hour incandescents.

http://www.centennialbulb.org

- Don Klipstein )