Say you've got an old circa 1954 ceiling light fixture. Spec'd for 2
max 40 watt incandescent bulbs.

My Sylvania 100w-output CFL's take 23w input.

100% safe to use 2 of these CFLs instead of 2 40w incandescents??

Thx,
Cathy

As long as the INPUT wattage is within the fixture's rating you are
fine. If the fixture is rated 40 W, then up to a 40 W INPUT lamp can be
used. The output equivalence is irrelevant in this respect.