Karin -

It would not be practical to use the new compact flourescent (energy saver) spiral bulbs.

One of the characteristics of these bulbs is that there is a pronounced 'warm up' time. It takes time for the bulb to rech peak light output. The actual time to reach peak output is probably around 4-5 minutes, depending on the manufacturer, but practically, the change in output is very noticeable during the first minute.

Most enlarging exposures are in the range of second, and rarely exceed one minute. In order to get predictable results, you need for enlarging lamp to have essentially constant output during this period so that the only variables that you have to deal with are the duration of the exposure and the lens aperture. If the lumen output of the enlarging lamp were to vary during the exposure, that would be an additional varible that would be extremely frustrating.

There are some enlargers (ie, so-called 'cold-light' enlargers) that use fluorescent-like light sources. These have either a provision to pre-warm the bulb, or else have a shutter so that the lamp can be left on continuously.