Oh hi Bill! Somehow I hadn't seen your post when I responded to this thread, but it prompted a PM when I did read it. I think with a 40 second exposure you will have a warm-up and then a period of quite steady light. The length of the warm-up will depend on the temperature at the start which increases as you use your enlarger. And even back-to-back test strip then final print could have slightly different proportion of that 40 seconds being in the warm-up stage. If we were talking about a 2 or 3 minute exposure, the peak brightness would occur in the middle somewhere ( probably around 20 seconds ), so it gets even more complicated! Hopefully my PM makes sense... it would be obvious if I could show you a couple of graphs.
Originally Posted by Bill Burk