Sorry for the stupid question, but what actually makes the lamp comes on, the tension applied to it, the eletric current that passes through it or the potency dissipated by it? I think its the current but I'm not sure and I don't know why? But if it were the current, what makes the lamp burn, and what makes it not comes on? I mean , I know that if it were the current, a big current will make it burn, but how much? A lamp of 4W and 1V for example, has a current of 4/1 = 4A, so 4,00001 A would burn it? And 3,999999 A would make it not comes on?