Installing Low-Voltage Outside Lights

Looking to take on the task of installing landscape lighting?

Installation of low voltage outside lights is something that instantly pays dividends. Not only do they give your house a more welcoming, inviting and warm appearance, but they also add a layer of security and safety to your home. If this sounds like the kind of job you want to take on yourself, then you’ll need to become familiar with the components of a landscape lighting system. Included on this list are the transformer, low-voltage lighting cable, fixtures, and bulbs. Here’s a quick breakdown on each of these components:


A transformer is an electrical device that converts (or transforms) a 120 volt current into a safer 12 volt current. This type of transformer is known as an electronic low-voltage transformer. It contains an electronic device called an inverter . The inverter is what actually converts a direct current (DC) to an alternating current (AC).

As a rule of thumb, it’s best to size your transformer based on the cumulative wattage all of the lights in the system will need, plus about 25% more for the cable. The additional wattage also accounts for the prevention of voltage drop (or a reduction in voltage), which occurs the further the line is away from the transformer. So lights closest to the transformer will shine brightest, and those furthest away will shine less so. The quality of the wires used in the system will also affect the degree of voltage drop.

To illustrate further and for the sake of simplicity, let’s say you have just purchased a system that includes 8 fixtures, each with a 10 watt lamp. The minimum amount of wattage you will need is 80 watts (8 fixtures x 10 watts = 80). Next you need to multiply 80 by 1.25 (or 25% more). So, 80 x 1.25 = 100. This is the size of the transformer you will need. You can increase the size of the transformer even further to account for additional fixtures you may add in the future; but generally it’s not advised to exceed the load wattage by more than 100%.


As you might guess, a low-voltage landscape lighting system requires specialized cables to run from the transformer to the fixtures. It is possible to install these cables without digging up or otherwise disturbing an intact landscape. This is done by stapling the cable firmly into place and covering it with dirt or mulch. But the usual method is to bury the cable in a 3 – 6 inch shallow entrenchment.

#12 SPT cable is the most commonly used wire in landscape lighting designs. This cable is composed of tightly bound strands of copper. This distinction sets it apart from wire, which is composed of a single strand of copper. But you will frequently hear the term “wire” used for “cable” when describing the line used in the lighting system.

SPT is an abbreviation for Service Parallel Thermoplastic, which describes the type of cable. #12 references the diameter of the copper strands, as set forth in the standard measurement guide of the American Wire Gauge (or AWG) in the United States. The larger the wire, the smaller the number for the cable. This means a #8 SPT cable has a larger diameter than a #12 SPT cable, and therefore is able to carry a greater electrical load.

Although #12 SPT cable is the standard, other sizes are also used in a residential landscape design. Pigtails (or the wires connected to the fixtures) are commonly #16 SPT cables. For instances when a wire runs longer distances, #8 or sometimes even #10 cables are used to handle the increased wattage load and to reduce voltage drop.


Low voltage landscape lighting fixtures come in all shapes, sizes and colors. When choosing fixtures, look for ones that are not just decorative, but also capable of being easily adjusted or moved as changes are made to your landscape.

Outdoor Area lights are designed to diffuse the light over a large object or area. These lights are also known as spot, wash, up, or outdoor flood lights. They are used to highlight bushes, trees, statues, walls, etc. When implemented skillfully, the effect of these lights can be dramatic.

Outdoor path lights are designed to illuminate the area just beneath and spread out within a few feet of the fixture. These lights are most commonly used on driveways and walkways. Generally, these lights should be spaced between 6 and 10 feet apart. What you don’t want is for your walkway or driveway to resemble a mini-runway.


The vast majority of bulbs used in landscape lighting designs today are halogen. These bulbs are energy efficient and shine a bright, white light. Depending on how bright you want the bulbs to shine, each halogen bulb can range from as low as 7 watts all the way up to 75 watts. Halogen bulbs typically last about 2500 hours. If your bulbs are in use an average of 8 hours per night, this means you can expect to use about 2920 hours each year (8 hours per night x 365 days per year = 2920 hours per year).

This stresses the importance of purchasing quality bulbs to start with and having replacement bulbs on hand. Always remember to replace a bulb as soon as it has burned out because, once a bulb has burned out, increased wattage is transferred to the next bulbs in line. This increased wattage causes these bulbs to subsequently burn out before their time. Another thing to consider is adjusting the amount of wattage in each bulb until you achieve just the right look you are after. Keeping a supply of different watt light bulbs allows you to experiment with different looks with each of the fixtures in your landscape lighting system.

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