Wiring a down-light into an existing lighting circuit is a great way to add illumination to an area without having to add a switch. A good place for adding a down-light would be an area or room where there are existing fixtures and switches, but you want to add more light to accent to a furniture piece or wall art. Kitchen islands and nook counters are also very popular places to add down-lights to supplement the existing illumination. Down-lights are perfect for projecting light exactly where you want it.
Examine your house circuit breaker box and locate the breaker that controls the existing lighting circuit you're augmenting. If the breaker is 20 amps you will need to use #12-2 romex wire for your jumper wires. If your breaker is 15 amps you will need #14-2 romex. Turn off the breaker that controls the circuit you'll be working on.
Measure and cut an opening in the ceiling for the new down-light fixture. Remove the fixture that is closest to the new down-light location. If it's recessed you can remove the bulb to reach the screws holding it in place around the inside of the can. Remove the screws and either push the recessed can into the ceiling or pull it through the hole and let it hang down into the room. You should now have access to the electrical box through the hole where the can was.
Install new romex cable from the existing light fixture to the new down-light location. If your adding more than one down-light add a jumper wire between each one. Each jumper wire has a black, a white and a bare copper ground.
Attach all the bare, and green if any, ground wires together in each location. Attach all black wires together in each location. Attach all white wires together in each location. Install the new down-light fixture.
Replace all of the fixtures, bulbs and trims and turn on the circuit breaker.
Recessed down-lights are easy to add. They can be hooked up, and hang through the hole you cut to install them. After all of the connections are made, just push the fixture into the hole, snap the support clips into place and install the trim and bulb.
Always turn off the breaker switch that supplies power to the circuit you are working on to avoid electric shock.