Nick Zentena said:
If you treat your household bulbs like enlarger bulbs don't be surprised if they don't outlast the enlarger bulbs.
To the intial question. Are you getting the same long times with both formats? Are you using a smaller lightbox for 35mm? Is the lightbox dirty inside?
I've no problem with times on my Beseler colour head. OTOH my Durst is slower. Both use the same bulbs.
Nick,
the enlarger bulbs are MUCH more expensive, and not available in Russia - so 50W gain just doesn't seem to be an adequate solution. So household mains halogen lamps in parabolic reflectors, fitting directly to my colour head and available freely, are just way easier
My Fuji CSD690 uses the same big lightbox with a movable white frame for 135 film (with smaller aperture). I get the same relatively long times with both formats (today I've printed something for my friend from 135 film, and the exposure was around 25 seconds on f/4, 80M filtration and 13*18cm print format).
The lightbox is not dirty inside, it's built in a funny yet good way: the light enters it through a slightly matted heat filter from its SIDE, not top, then the foam white walls reflect it to three (!!!) center filters. These are just plates of glass with some kind of dot pattern printed on them with white enamel, denser in centre, more loose to the edges. Finally the mixed and levelled light reaches a bottom plate of light box, made from thick opal plastic. So no wonder that this box eats away PLENTY of light - but it makes the remainder very good-behaving, soft and perfectly even. I don't know why Fuji engineers have decided to make it that way, really - but it works

That's probably the way the enlarger was engineered

Again, even with 200W of power (both focusing and printing lamps on), I can't say I get the whole additional stop of light, judging by the test exposures...
My safelighting does not fog the VC paper even after half-an-hour exposure, so it's not a problem too. Really, the prints come out with a very good sharpness and gradation, with no trace of fog, so I think the machine should just work that way
And the lenses give the same excellent sharpness and contrast at both their maximum apertures (2.8 and 5.6 resp.) and stopped down to 1-2 stops. No focus shift or distortion. It looks like some stopping is more important to Tessar-type enlaring lenses - with 6-lens Fujinons and Rodagons the maximum aperture can be used for work, unless someone wants to tilt the easel a bit to correct the convergence, needing bigger DOF in printing.
Cheers, and thanks for your advices - Zhenya