good they are of the same watts, in fact probe putting both on the right side and gives the total light high, only when putting the other on the left side does not give the total light high, that is my observation I wait for your response
Then verify that the cables have good contact and more important the mass or negative. If you do not look at the filaments, that inside the lamp they are not twisted. This sometimes happens with defiant lparas that come with failure.