Welcome to the forum. Can you provide a little more info on what you are looking for? In a series circuit and if all the bulbs are the same make, model, and wattage, they are should be the same brightness.
The best example of this is the old "all American five" tube radio where they had tube filaments ranging from 12v to 50v and they all used 150MA but the effective resistance was selected so they could take 120v line power in series to light them all up. (The octal set was 12SA7 converter, 12SK7 IF amp, 12SQ7 audio detector and signal amp, 50L6 audio power, and 35Z5 rectifier). Later they came out with a 100MA "miniature" string but it worked the same. That was what we had in your basic table radio until the late 60s early 70s when transistors took over. I still believe the tube radios were better at pulling in distant stations and sounded better but that is just old guy nostalgia.
Greg LOL. Skeeter, another good example: You have a 24 volt power supply. But you do not have any 24 volt bulbs. But you do have 12 volt bulbs. If you put two 12 volt bulbs in series with the 24 volt supply you will have 12 volts at the mid point between the bulbs and the supply. But you still have 24 volts output at the supply.
If they are the same wattage AND the same voltage rating, then the bulbs should be the same brightness. If they are then you may just have a bad bulb. I would let both bulbs cool off and ohm them out and see what you get.