The message
from "Bioboffin" contains these words:

That's very dependent on the make and model. We've some that start in
ten seconds or so, others that take more.

I find the slow warm up is a benefit first thing in the morning in winter.

We have Ikea R50 spots in our bedside reading lamps. Very gentle on the
brain, they are, taking about 30 seconds to get even half-way.

--
Skipweasel
Pay no attention to that man behind the curtain.