Turn on a table lamp in the socket. Repeatedly press the switch button. The bulb does not burn. Remove the bulb from the socket and show that it is completely intact. Put it in place. Pressing the switch button and say the magic phrase: "Light, Sargis!" This time, the bulb will light up.
The secret of focus will not guess only very small audience. The fact that you pre-slightly twisted the bulb from the socket. So it is not burned. Before the show turned the bulb on the audience, leave the button switch in the off position. Show the audience that the bulb fit, thereby averting unnecessary suspicion. Replace the bulb, this time to the end. Now after your "spells" it will light up immediately.