How to Design a Low Voltage Outdoor Lighting System

How to Design a Low Voltage Outdoor Lighting System - click to enlargeHow to Design a Low Voltage Outdoor Lighting System

Low voltage
(12 volt) systems are popular for landscape lighting for many good reasons. Low voltage systems are perfect for creative highlighting of trees, gardens, artwork and other landscape features. Low voltage fixtures are easy to install. Low voltage cable can be buried in a shallow trench, run through conduit or buried underground. A low voltage system is flexible. You can easily move fixtures to accomodate plant growth or to change lighting effects. Low voltage systems are safe and energy efficient. Transformers reduce standard voltage from 120 volts to a safe 12 volts. There is no risk of electrical shock to children or animals if the cable is accidentally cut. Lamps use less wattage and may not have the brightness of 120 volt, higher wattage lamps.

Deciding what you want to light and which techniques to use.

The first step in designing any lighting system is to determine what you want the light to do for you. Walk around your property, look out your windows and doors, and think about the kind of mood you would like to create. Look for possible focal points for dramatic accent lighting or plan for soft but safe pathway lighting. Create romantic shadows with subtle moonlighting or make entertainment areas come alive with bright party lighting. Next; review the techniques of accent lighting. Select the technique you feel best achieves the mood you with to create. Some light will "spill" from the accent areas. Work outward from these accent points to fill in areas with path or spead lighting. Balance and subtlety are key tools in path and spread lighting. Try out different techniques, and have fun discovering the beauty of your yard at night. Be sure that when you place your fixtures they will not interfere with lawnmowers, traffic or be a source of irritating glare inside your house or to your neighbors.

Using Photometrics

Once you have developed your lighting plan, select the style of fixture and lamps that best fit your needs. Use the photometric charts and the lamp guide.PDF to select lamp types and to determine light output and beam spreads. Remember, sometimes less is do not need high levels of illumination coming from individual fixtures. Instead, use several fixtures at lower wattages for better effect.

You will need Adobe Acrobat Reader to view the above PDF files. You may download the program for free by clicking here

Selecting Transformers

Low voltage systems require the use of transformer to reduce standard 120 volt power from your home to 12 volts. To determine the transformer size you will need, add up the wattages of all lamps you plan to use. Select a transformer that matches as closely as possible the total lamp wattage. For example: if you have 11 fixtures all rated at 24.4 watts-you will need a 300 watt (VA) transformer. (11 x 24.4 = 268.4 watts). Generally, the total lamp load should not be less that one-third the transformer's wattage rating, nor exceed its maximum watttage capacity. If your total wattage is too high, either divide the load between two transformers or use a more powerful transformer. Refer to the transformers section.

Planning Low Voltage Layouts

These diagrams show some of the most common low voltage cable layouts. Your choice of layout can help minimize voltage drop.

1. Straight run installation
Fixtures run in sequence directly from the transformer. Loop Instalation, low voltage lighting

2. Loop installation
Helps reduce voltage drop and produces a more uniform light output. It is important that you connect the same wire leads to the proper transformer terminals by noting the ridge or marking on one side of the cable.

Low voltage layoutslighting

3. Split load installation
Run up to the recommended maximum cable length in two or more directions from the transformer.

4. "I" Installation
Allows more equal distribution of power to the center of a run, or to a run some distance away. Cable running from transformer must be of a heavier gauge (8 or 10 gauge).

kichler lightingkichler low voltage

How to minimize Voltage Drop

The closer your lamps are placed to the transformer, the higher their voltage (and wattage) readings will be. Those farthest away will have lower voltages. If a cable run is too long, or it too many lights are being powered by a single transformer, noticable voltage drop may occur. Voltage drop causes the lights farthest from the transformer to become dim. Voltage drop can be minimized in several different ways:

  • use heavier gauge cable 8 gauge K-15503 BK 10 gauge K-15504 BK
  • use a higher rated transformer
  • multiple taps 12-13-14
  • use multiple transformers
  • shorten cable lengths
  • reduce individual fixture wattages
  • reduce the total number of fixtures on a run Voltage drop can actually work to your advantage if differences in lamp brightness levels are not objectionable. Lower voltage will extend the life of a lamp, requiring less frequent replacement.

Selecting Mounting Accessories

After you have selected fixtures, lamps, transformers and cables, the only thing left is to select mounting accesories. These might include stems, stakes, bollards and sheilding accessories.

Designing Line Voltage Systems

Line voltage (120 volt) systems are used where brilliant illumination is required for safety or security, for lighting large areas, or when you must light from farther away, such as uplighting large trees. In many cases, a landscape lighting design can be developed using both line voltage and low voltage components. The same steps used to design a low voltage system apply when designing landscape lighting using a line voltage system. Focus attention on the key points of interest using accent lighting. Provide for safe access of walkways and stairs. Illuminate activity areas as needed to maintain the mood you wish to achieve. Installation of a line voltage system is more complicated than a low voltage system. We recommend always working with a professional electrical contractor to make sure that your system is installed correctly and meets local electrical codes and requirements.

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