Quote Originally Posted by Bill Burk View Post
...I put a meter similar to Nicholas' under the brightest (shadow) spot and change my f/stop on the enlarging lens until it "nulls" at the point where my time should be 32 seconds. ... Even still, I sometimes have print-to-print variations that I blame on variations in brightness of the old fluorescent ring light source. ... For now I am settling on my old "null" meter and pledging to check before each print.
You might want to do a dummy print and see how much the light output changes over your standard 32 second printing time. The light change over the printing time should be small when the lamp has warmed up but may be quite large if you are starting with a cold lamp.

For the most consistent results you might try turning the enlarger on and waiting until the meter reading stops climbing before making a print - that way you will always be working with a hot lamp.

Even an incandescent condenser head has a few minute stabilization time during which the light output rises by 0.03 stops or so - admittedly irrelevant for printing but interesting for the technoids among us.