How To Design Your 12 Volt Outdoor Lighting System By Kimberly Quang At Isnare.com Ezine Articles

Fixture - a housing and the electrical components contained in that housing, a luminaire.

Lamp - a light bulb.

Transformer - an electrical power source; this device is required to operate any low voltage fixture, in this case 12-volts.

Circuit - a closed, usually circular electrical line that leaves a transformer (positive) and returns to the transformer (common)

Design Voltage - the amount of voltage a fixture is designed to operate on; the actual voltage that you supply may be more or less depending on the wiring method.

Fixture and Lamp Selection

The fixtures and lamps are selected after determining which features of your landscaping are to be used. Decorative fixtures will be placed in plain sight; otherwise, conceal the light source when possible.

Bullet/Directional Lights - These designs help focus and direct the light beams. Some also cut off glare and protect the lamp and socket from debris and moisture.

Area/Path/Bollard Lights - These low level units are designed to cast illumination in a broader pattern for: flower beds, perimeter plantings, driveways, steps and paths.

In-ground/Well Lights - Burying these fixtures flush with the ground conceals the light source. Use for up-lighting trees and shrubs, an grazing textured walls.

Accent/Spot Lights - Versatile/adjustable fixtures used for up-lighting, cross lighting, accenting and grazing. When mounted high up provide focused down-lighting and moonlighting.

Deck/Step/Brick Lights - These wall mount fixtures light pathways, steps, garden walks, deck and pool areas.

Incandescent lamps are the standard type commonly used around the home. They are inexpensive but yield less light than other bulbs. Halogen and Quartz lamps are a compact light source which provides a consistently bright light. These are available as a reflector (MR) and as a projector (PAR) type for controlling the direction of the light. These fit into smaller and less obtrusive fixtures.

Mounting Method

The mounting method is determined by the location of the fixture. Metal canopies allow you to mount fixtures to a deck or soffit, while plastic stakes are for mounting into the ground. There is an extensive variety of selection in mounting hardware, so check to see which kind is offered with your light fixture.

Power Cable

It is important to note that the cable referred to in this document is two-pronged; i.e., there are two independent wires inside.

The cable lengths in your design will determine many further aspects of your lighting system. You want a cable wire that will deliver the best voltage to each individual fixture, and the best method for selecting this cable begins with a layout of your project. Be sure to include all landscape features, buildings, individual light fixtures, and power supplies in your drawing.

Group your light fixtures into clusters of 2 to 6; do not form a group whose total wattages exceed 240 Watts. One cluster at a time, select a fixture -or a point between two fixtures- that is the most centralized and draw a line from the power supply to this point (your center point). From the center point, draw a line to the nearest fixture on the right, and do the same for the nearest fixture to the left. Repeat this process from the two newly connected fixtures until the entire cluster is connected. Click here to view a sample layout.

To achieve this wiring method, you will need a common device known as a T-connector. The T-connector allows you to place your cable along the path of the lights, cut the cable at the last light, and then connect the middle of the laid-out cable to a new piece of cable that will run back to the power supply. Then you will use a similar item known as a Quick Connector to fasten the laid-out cable to each light fixture. These Quick Connectors are included with most low-voltage outdoor landscape lights. If quick connection devices are not available, you can use a common wire nut. Place a small bead of household silicone seal inside the wire nut to create a water-tight fit. Here is an example of a typical layout. The "T" stands for the Transformer, and the "35" represents a 35 Watt light fixture.

Now you must determine the amount of voltage being delivered to each fixture of each cluster. Though you may start with 12 Volts, there is a phenomenon called voltage drop that will reduce the voltage being delivered to each fixture. Voltage drop on your system will affect lamp life and the amount of light the lamps will deliver. Too much voltage drop lowers the light output and changes the color of the light. Too little voltage drop burns the lamps too hot and shortens the lamp life. A good rule of thumb to prevent voltage drop is no more than 100 Watts on 100 feet of 12/2 cable.

Another very effective way to eliminate voltage drop is to use continuous loop wiring. This entails the same preparation as the T-connector method, except you lay the cable from the transformer, along side each light fixture (one cluster per cable), and back to the transformer. To achieve continuous loop, simply connect both ends of one wire of the cable to the Positive lead and both ends of the other wire of the cable to the Common lead. Be very careful to not mix these connections! The two internal wires can be distinguished by their markings. One will have a solid color and the other will have writing, a stripe, or a different solid color. Sometimes, a lighting designer or a home owner will want to take advantage of voltage drop.

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