After 25 years of incandescence and collimation, a cold light bulb went off in my head, and I decided to get an Aristo Cold Light head for my D2. So far so good, except that my exposures are now 2 stops greater than previous prints of the same negatives, and the light looks very dim in the dark. Hardly enough to read the f stop on the lens. The installation was straightforward; the unit matches the enlarger; the diffusion panel is stock Aristo; it came with instructions (which I followed explicitly, thank you); and I am using the heater a full half hour prior to making art. Question: Have others noted that the cold light is dimmer than a 75W bulb? Is my unit underperforming or my bulb going south?