Thanks to Ed Thurstan for the results of his neat experiment comparing the light up time of the new-fangled fluoro bulbs compared to the perfectly OK old incandescent bulbs that we now can not buy.
As Ed says:
My 75W incandescent bedside lamp bulb finally failed. So I installed a Philips 18W “Ambiance” fluoro, which is claimed to be equivalent to 100W Incandescent bulb. It emitted a dull glow befitting a mood light in a funeral parlour.
After waiting several minutes for sufficient light to see what I was doing, I set up an experiment with a digital camera to measure the light intensity from the fluoro, and compare it with ancient 60 and 75W incandescent bulbs still working around the house.
I set the camera on a tripod, aimed at a spot illuminated by the lamp. I set the camera to take a shot every 15 seconds, with the aperture and ISO fixed but the shutter speed allowed to vary to maintain a constant exposure.
Then I ran each of the three bulbs through a trial to see how long each took to achieve their maximum intensity from when the lamp was switched on. So the shutter speeds give a direct measure of light intensity.
Finally I normalised the results relative to the maximum intensity of the fluoro being treated as 1.