FYI
Aristo coldlights do have an additional heater above the light chamber. Aristo calls it the thermo and there is a separate cord with which to plug in. There is some temperature control there, too. If one measures the light output versus temperature, you will notice as the temperature increases, the light output increases to some maximum at which point the light output will decrease with temperature. It is at this point that one hopes the light chamber's temperature is regulated. Of course, turning on the lamp will heat the lamp, too. I believe this increase in light output with temperature is dominated by the phosphor temperature, as I've cooled spots on my tube with canned air, and there forms a little dim spot. ( Don't do this yourself as you could crack the tube. )
Small differences in print exposures can be noticed in productions runs especially, but also in single prints in critical highlights. As highlights in prints get very little exposure above threshold, the slightest change in overall exposure can move the highlight exposure above or below threshold.
If you use a coldlight, you pretty much have to have a light integrator or stabilizer. Personally, I use a MetroLux and expusure are perfectly repeatable, even when the exposure is broken into many pieces, as MetroLux includes the decay light (after the lamp is turned off) in the exposure.
