Low-voltage LED landscape lighting

How the system works

The heart of the system is a transformer, a box mounted on the house or a post that converts 120 volt household power to about 12 volts. The transformer plugs into a GFCI protected outdoor outlet with a weatherproof in-use cover. The National Electrical Code requires GFCI protection on outdoor receptacles, and Article 411 covers lighting systems that run at 30 volts or less.

A licensed electrician installs the outlet and mounts and connects the transformer. We do not do line-voltage electrical work. Our part starts on the low-voltage side: laying out the fixtures, running and burying the cable, making the connections, and aiming the lights.

From the transformer, low-voltage cable runs out to the fixtures. The code sets 6 inches of cover as the minimum for landscape lighting cable at 30 volts or less in a yard, and 18 inches under a residential driveway. We bury cable at or below 6 inches in lawns and beds and sleeve it in conduit where it crosses under a walk or patio.

Fixture types

Path lights are short fixtures on a stake with a hood that throws light down and out onto a walkway. They are spaced along a path, usually staggered from side to side, so the ground is lit without every light shining into people's eyes. Too many path lights in a straight line make a walk look like a runway.

Uplights sit at the base of a tree, a column, or the front of the house and aim upward. They are what give a house or a large tree its shape at night. Wall wash lights are wider beam fixtures set back from a wall or a stone face to spread even light across it. Both are aimed so the light falls on the target and not into windows or the neighbor's yard.

Step lights mount in the riser of a step or the face of a wall and throw light down onto the tread. They are the safest way to light steps because each tread is lit from just above it, with no fixture in the walking path. Step and wall lights are easiest to install when the steps or wall are being built, since the cable can be run through the block before the cap goes on. That is one reason we plan lighting with hardscape projects.

Wire sizing and voltage drop

Voltage drops along the length of a cable, and the drop gets larger as the run gets longer and the load on it gets heavier. On a 12 volt system a small drop is a large share of the voltage. Fixtures at the end of an undersized run get less voltage and look dimmer or shift in color compared to the ones near the transformer.

Lighting manufacturers give general guidance on cable size. A 12 gauge cable carries about 100 feet cleanly with a load of 100 watts or less, and longer or heavier runs step up to 10 gauge or larger. The target is to keep every fixture within about 10 percent of the transformer's output, so on a 12 volt system no fixture drops much below about 10.8 volts. We measure voltage at the far fixture before the trench is closed.

Transformers are sized so the total fixture load stays at or below about 80 percent of the transformer's rating. That leaves room for voltage stability and for adding fixtures later. Many transformers have multiple taps, for example 12, 13, 14, and 15 volts, so a long run can be fed from a higher tap to make up for the drop along the cable.

Hub wiring vs daisy chain

In a daisy chain, one cable runs out from the transformer and each fixture connects to it in turn. It uses the least cable, but every fixture sees a little less voltage than the one before it. On a short run with a few fixtures this is fine. On a long run the last lights are visibly dimmer.

In a hub layout, a single heavier cable runs from the transformer to a central point, and shorter leads branch from that hub to each fixture. Every fixture sits at about the same distance from the power source, so they all get close to the same voltage. Hub wiring takes more planning and more connections, and it is how we lay out most systems with more than a handful of fixtures.

A loop layout is a third option, where the cable runs out to the fixtures and back to the transformer so power feeds from both ends. It is useful along a long driveway edge or a property line where the fixtures are in one long row.

Timers, photocells, and control

Most transformers come with a photocell, a small sensor that turns the lights on at dusk and off at dawn. A photocell alone leaves the lights on all night, which is why most systems pair it with a timer that shuts them off at a set hour.

An astronomic timer adjusts the on time to sunset through the year without a photocell, which avoids problems when the sensor is shaded by a tree or lit by a porch light. Many newer transformers connect to a phone app or a home automation system, so zones can be scheduled separately. A common setup is front yard lights on until midnight and step lights on until sunrise.

If the lights are wired in separate zones back to the transformer, each zone can have its own schedule. That is easier to plan before the cable goes in than to add after.

Lumens and color temperature

Lumens measure how much light a fixture puts out. Landscape lighting needs far less than most people expect. Path and step lights are low output, usually a few hundred lumens or less, because they light the ground a few feet away. Uplights on a large tree or the face of a house run higher. Starting lower and adjusting after dark avoids glare and a yard that looks overlit.

Color temperature is measured in kelvin. Warm white in the range of 2700K to 3000K is standard for residential landscape lighting. It flatters stone, brick, siding, and plants, and it matches the interior light coming through the windows. Cooler light, 4000K and up, looks harsh against a house and makes greenery look gray.

Keep the color temperature the same across every fixture in view. A mix of 2700K and 4000K fixtures in the same yard is obvious at night. Many LED fixtures now allow the color temperature or output to be adjusted, which helps match fixtures added in later years.

Maintenance

LED landscape systems need much less upkeep than the old halogen systems, since there are no bulbs to replace every year or two. The work that remains is mostly keeping the fixtures clear. Mulch piles up over path lights, shrubs grow in front of uplights, and lawn care equipment knocks fixtures out of aim.

Once a year, usually in spring, walk the yard at night and check every fixture. Straighten leaning stakes, clean lenses and well lights of dirt and leaves, trim plants blocking the beam, and check that the timer matches the season. Fixtures that flicker or go dark usually point to a loose connection or a nicked cable, often from an edging tool or aeration.

Tell anyone doing lawn aeration, bed edging, or planting where the cable runs. A simple sketch of the layout kept with the transformer manual saves a lot of digging later. If a problem is on the line-voltage side, such as the outlet or the transformer not powering up, that goes to a licensed electrician.

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