Rav Chaim Ozer's Lightbulb Havdalah Ruling
To publicize that turning on a lightbulb on Shabbos is lighting a fire, Rav Chaim Ozer Grodzinski ruled that an incandescent bulb may be used for Havdalah.
There is an interesting story related about Rav Chaim Ozer Grodzinski (d. 1940), a preeminent av beis din in Vilnius, Lithuania. With the advent of the lightbulb, people were unsure whether it was permitted to turn off and on the lights on Shabbos. Rav Chaim Ozer was adamant that turning on an incandescent lightbulb is the equivalent of lighting a fire on Shabbos and is therefore absolutely forbidden. To publicize his psak, he ruled that an incandescent lightbulb may be used for Havdallah because it is the same as reciting a berachah over fire. This psak was not universally accepted.