Usage mostly, I guess? My family was big on energy efficiency growing up so we were always on the lookout for better fluorescent bulbs, and dang near celebrated when an incandescent got replaced with one--and the rare occasion where an older fluorescent burned out and could be replaced with something more efficient. Got real familiar with color temperature thanks to that.

I also am old enough that I got to watch blue and white LEDs show up on the market in real time as components, then flashlights, then bulbs. I've always had a penchant for electronics so I had piles of loose LEDs around.

Combine that with some outdoorsiness and untrustworthy infrastructure and I had a good collection of weird flashlights when I was a kid. When the first LED flashlights showed up, it was a complete game changer in terms of battery life and brightness. For a while the go-to for us was just blue LED keychain lights because they were dirt cheap, lasted forever, and were brighter than the old lights.

Eventually, this xkcd triggered my sleeper-agent programming and I went nuts with "enthusiast" flashlights. That led to "shit, these are brighter than my room lighting, better fix that"--and a 3 lb 5000 lumen LED corncob designed for gymnasiums dangling over my couch.

Nowadays, thanks to their low power draw, absurd output, and improved heat management you can stick a 6000 lumen photon cannon in a little reading lamp meant for a 40 watt incandescent.

If you're hunting for good bulbs, the big light quality differentiators are color temp, CRI, and flicker. Dimmable & brightness needs vary.

• Color Temp: ≤3500K is cozy, 4000-4500K feels neutral, 5000k+ is blue. Yes, lower numbers are "warmer" and higher numbers are "cooler" and I will never not be mad about those terms
• Color Rendering Index (CRI): the higher the better. LEDs don't necessarily produce a continuous spectrum like incandescents do
  • 60 is the worst waiting room you've ever been in
  • 80 is comparable to your average office fluorescent tubes
  • 90 is getting pretty good, easily enough for places you aren't spending all your time
  • 95+ is top tier LEDs, things will look right
  • 100 is daylight from the sun/incandescence, the standard that defines the scale
• Flicker: honestly if anyone is still making AC LED bulbs that noticeably flicker/strobe they should be tarred and feathered but it's still something to watch out for in product reviews.

If you get real nerdy about it LEDs also inherently have a tint because the white phosphor blend is gonna have a peak somewhere in the spectrum but that isn't usually relevant--it's only notable when that peak doesn't align with the color temperature. The flashlight folks tend to speak fondly of rosy/pink and despise green.