Hello,
I am lucky and still have an original Philips lamp 6604 for my Leitz Focomat V35 enlarger.
I made some tests to see what the lux is at different aperture and hights of the enlarger . I used the android lux app : Lux meter.
So you can compare the lux readings of your alternative lamps such as the Philips 13139 or Osram EFN 75W, 12V with the original Philips 6604 lamp.
No negative in carrier, full dark in darkroom, lux measurements readings in the middle, left under corner and right upper corner on the baseboard of the enlarger.
The results are;
I am lucky and still have an original Philips lamp 6604 for my Leitz Focomat V35 enlarger.
I made some tests to see what the lux is at different aperture and hights of the enlarger . I used the android lux app : Lux meter.
So you can compare the lux readings of your alternative lamps such as the Philips 13139 or Osram EFN 75W, 12V with the original Philips 6604 lamp.
No negative in carrier, full dark in darkroom, lux measurements readings in the middle, left under corner and right upper corner on the baseboard of the enlarger.
The results are;