Two filament bulbs A and B are connected in series combination. Filament of A is made of carbon and that of B is made of platinum. At t=0, the combination is connected to a d.c. source. Then after a long time

The same current flowing through the filaments of A and B with the rise of temperature, resistivity of carbon decreases and that of platinum increases since rate of heat generation is i2R,and brightness is proportional to rate of heat generation. Energy loss or heat is more where resistance is more.