Your question as to why we use light bulbs, is answered as follows: light bulbs are also a part of Krsna's energy. Just as we use automobiles, adding machines, typewriters, dictaphone etc.
Whatever is there should be employed in service of Krsna. Without using matter in service of Krsna it becomes the cause of bondage, but by using it in the service of Krsna it helps us to become Krsna conscious.