Tools & Materials
Decks are usually built with summer days in mind, but the entertaining doesn’t have to stop when the sun goes down. Adding outdoor-rated LEDs can illuminate your space in a way that promotes both safe footing and appealing ambience—versus the harsh shadows you get from a spotlight on the house. Learn how to install low voltage deck lighting with this guide.
“Low-voltage lighting is very DIY-friendly,” says Scott Caron, master electrician for Ask This Old House. “The thin wiring is easy to hide on or under the deck.” In addition to putting up festive string lights, he installed three kinds of LEDs on this deck in San Antonio, allowing the homeowners to enjoy their Lone Star evenings. For your own project, start by deciding where to place the transformer, which steps the power down to 12 volts: It needs to plug in to a standard 110-volt outlet, and all your wiring routes back to this point.
Day 1: Install the lights (Steps 2-9).
Day 2: Wire the lights to the transformer (Steps 10-14).
Post light, $92; LED ledge and rail light, $107; up/down light, $128; all in copper, from Focus Industries
Drill a Hole for Wiring
Mark the center of a post about 12 inches above the deck—high enough for the light to illuminate the decking but not so high that it will blind seated guests. Use a paddle bit to drill a inch-diameter hole through the post, as shown. Repeat for every post.
Screw on Post Light
Fish the LED wire through the housing and fresh hole. Attach the fixture to the post with supplied screws, as shown. Secure the wire to the back side of the post with low-voltage staples. Continue stapling every few inches, carrying the wire to the next fixture by tucking it under the handrail or the deck’s framing (you’ll wire it later).
Build Out the Treads
The stairway lights mount to the treads overhanging the risers. If your tread doesn’t have an overhang of at least 1 inch, add one with a 2×2 pressure-treated pine baluster. Measure the width of the tread and cut the piece to fit with a circular saw. Evenly space pilot holes along the front edge of the baluster for 2-inch deck screws. Attach the fixture to the middle of the baluster with supplied screws, as shown, then repeat the process on the remaining treads.
Drill a Pass-Through
Drill a inch-diameter hole in the riser just below the tread to accept the fixture’s wire. Fish the loose end of the wire into the hole, as shown. Repeat the process on the remaining treads.
Fasten the Fixture in Place
Add a bead of polyurethane adhesive to the baluster, then screw the baluster to the tread, as shown, oriented with the LEDs facing the step below. Repeat this process on the remaining treads, then stain the balusters to match the deck.
Cut a Hole
Locate uplights in the center of deck boards about a foot from the tree to illuminate the bark and the canopy. Use a 2-inch hole saw to cut a hole for each light.
Thread the wire into the hole, then press-fit the light in place.
Strip the Wires
Use 14-gauge wire to daisy chain all the lights of a certain type together—post lights to post lights, for example. To start, use wire strippers to remove about an inch of insulation from the wires attached to the light farthest from the transformer. Measure the distance between this light and the next one and cut a length of 14-gauge wire to that length. Split the 14-gauge wire apart, then strip all four ends.
Add Compression Connections
Insert the first light’s ribbed or marked negative wire into one end of the brass compression connection and tighten the set screw with a hex wrench, as shown. Slip the heat-shrink tubing over the connection, then add the ribbed 14-gauge wire to the other end of the connection and tighten it. Repeat the process on the smooth or unmarked positive wires of the same fixture.
Shrink the Wrap
Cover the connection with the heat-shrink tubing, then pass a torch or heat gun over the wrap, holding it a few inches away, to form a watertight seal, as shown. Continue daisy chaining lights in the series until you reach the one closest to the transformer. Add enough 14-gauge wire to reach the transformer, and secure the connections with waterproof wire nuts. Now join the three 14-gauge wires (positives together and negatives together) and add another section of 14-gauge wire to serve as a pigtail. Hide the wiring under the deck or secure it out of sight with staples.
Mount the Box
The bottom of the transformer must be at least 1 foot off the ground and within 2 feet of a standard 110-volt outlet. We placed ours inside the house to keep the timer easily accessible. First, use deck screws to attach the mounting bracket to the wall, checking for level with a torpedo level. Attach the transformer to the bracket.
Wire the Box
Bring the pigtail to the box and thread it through the knockout in the bottom, as shown. Use a small flathead screwdriver to tighten the negative wire into the terminal labeled “common” and the positive wire into the 12.5-volt terminal. Plug the transformer into the 110-volt outlet, then flip the switch to test the lights. Set the timer and install the cover.