I am looking for way how to do relative calibration of light sensor (PMT). I would appreciate any suggestions or links to sources with description how to do it in very simple (understand also cheap if possible) way. For example. Let say that I have integration sphere with two outpust. I have two optical cables connecting to sphere. Lets assume that those two cables are identical. Optical cable enlight PMT sensor from some distance in black box. I can measure light characterstics by PMT (not calibrated). With distribution maximum at point I_max_one_source. If I connect two cables from integration sphere to black box, playing role of two very close sources, should I see 2 times more pulses on PMT? So will I see distribution with maximum at point I_max_two_sources = 2 x I_max_one_source? Any other way or suggestions how to do simple calbration are appreciated. Thanks for answers to naive questions from beginner in the field.