Probably the weirdest kind of lightbulb I’ve heard of is the electron stimulated luminescence bulb.

They were basically little CRT screens that produced white light instead of a picture. They had about the same efficiency and lifespan as CFL bulbs (which were around at the same time) but better color rendering capability (higher CRI). They also didn’t use mercury in their construction.

They never caught on probably because of how bulky they were, with cost probably being a factor as well (though if they were as manufactured at the scales CFLs were the cost may have come down). Today LEDs are better than both of course.

Speaking of cost and LEDs, it’s pretty remarkable just how cheap lighting has gotten. Consider this article, where they talk about the cost of producing light with candles vs with incandescent bulbs. But since 2006 we have developed some LED bulbs that approach or exceed 200 lumens per watt. That’s a more than 11x improvement over the 17 lumens per watt figure given in that article. That adds another .9 to the percentage cost drop before we even consider the longer lifetime of the LED bulb.

I think I calculated at some point that Philips Ultra Efficient bulbs cost less than $1 per year per bulb to operate if you add the cost of power + the purchase price of the bulb amortized over its lifetime. At this point lighting up a room is almost free.