The entrance and bathroom (as in bath room, American readers) ones seem instantaneous.

In the living room there are two. One looks pretty much instantaneous. Strangely, the other one seems to vary, it sometimes take a while, but the immediate light is quite enough to be useful.

Now, none of those was sold as having no significant heating up time. You can get some of those, but they don't have quite the same energy saving so I didn't.
On the other hand, I'm not sure about the power conversions. The manufacturer will claim it's as bright as a so many watts incandescent bulb, and sometimes I'm not too sure it's quite true.

I've never had to change one.

LEDs are brightest of all, by some distance, and last forever.

Earth provides enough to satisfy every man's need, but not every man's greed. Gandhi