Plug a sound-activating switching device into a wall outlet close to the light you wish to control.
Run the power cable from the light over to the device and plug the light into the device's port. Some devices have multiple ports so they can control several lights through sound.
Turn on the light manually. Once it has power, the sound-activated switching device will turn it on and off based on your auditory commands. If the outlet is connected to a light switch in the bedroom, the switch should be on at all times for the sound-activated switching device to work.