To separate the operation of two lights in a room, consider replacing the single switch with a double switch. The double switch lets you operate each light on its own switch, allowing you to turn only the light you need on and leave the other light off. A double switch uses the same space as the original switch. You do not have to cut the drywall to expand the size of the switch box. Wire the double switch using the existing wiring from the single switch.
Turn off the breaker that supplies power to the circuit. A test on the circuit will verify you turned off the right breaker. Touch one lead from the two-lead tester to the black wire inside the switch box leading back to the circuit panel. The tester will not light if you turned off the right breaker. There are two other black wires inside the switch box that lead to each light fixture; these will not have power running through them until connected to the switch.
Tie the three white wires together inside the switch box, two white wires connected to the two separate lights and the white wire from the circuit panel. Twist one red wire connector clockwise onto all three white wires to tie them together. Push this set of wires to the back of the switch box.
Connect the three bare copper ground wires together from inside the switch box, the two bare copper wires that lead to the two separate lights and the bare copper wire that leads back to the circuit panel. Use an additional red wire connector on all three wires, connecting them. Push the set of bare copper wires into the switch box next to the set of white wires.
Wrap the black wire from the circuit panel around the brass screw on the right side of the double switch. Tighten the screw to hold the wire. The circuit panel black wire supplies electricity to the double switch.
Wrap one black wire from one of the light fixtures around one of the brass screws on the left side of the double switch. Wrap the remaining light fixture wire around the remaining screw on the side of the double switch. Tighten both brass screws to hold the black wires from the light fixtures to the double switch.
Install the double switch inside the switch box. Push the switch and its wires into the box, connecting the switch to the box at the top and bottom using the screws that came with the double switch. Cover the switch with a duplex cover plate and turn on the breaker to the circuit.