How to Design an Outdoor Lighting System

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 if a single transformer is powering too many lights, noticeable voltage drop may occur. (Voltage should not be lower than 10.8 V or greater than 12 V.) 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.
• Use 8-gauge K-15503 BK.
• Use 10-gauge K-15504 BK.
• Use a higher rated transformer.
• Multiple taps 12-13-14.
• Use multiple transformers.
• Shorten cable lengths.
• Reduce individual fixture wattage.
• Reduce the total number of fixtures on a run.
• Use K-15520 Voltage Enhancer.

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 NONELECTRICAL ACCESSORIES. By now you should have a list of fixtures, their lamps, one or more transformers and cable requirements. The only thing left is to select nonelectrical accessories. These might include mounting accessories like stems, stakes, bollards and shielding accessories.

DESIGNING A LINE VOLTAGE SYSTEM. Line voltage (120 V) systems are used where brilliant illumination is required for safety or security, for lighting large areas or for spots where 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 on 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. It is recommended that you always work with a professional electrical contractor to make sure that your system is installed correctly and meets local electrical codes and requirements.

DESIGNING A LOW VOLTAGE SYSTEM. Low voltage (120 V) systems are becoming more popular for landscape lighting for many good reasons. Low voltage systems are perfect for creative highlighting of trees, gardens, artwork and other landscaping features.

Low voltage fixtures are easy to install. Low voltage cable can be buried in a shallow trench or even run on top of the ground, if desired. It does not need to run through conduit or be buried deeply in the ground.

A low voltage system is flexible. You can easily move fixtures to accommodate plant growth or to change lighting effects.

Low voltage systems are safe and energy efficient. Transformers reduce standard voltage from 120 V to a safe 12 V. There is no risk of electrical shock to children or animals if the cable is accidentally cut. Lamps use less wattage yet provide comparable performance to many 120 V, 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 wish to create. Note that some light will "spill" from the accent areas. Work outward from these accent points to fill in areas with path or spread 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 lawn mowers or traffic or be a source of irritating glare.

CHOOSING FIXTURES AND LAMPS. Once you have developed your lighting plan, select the style of fixture and lamps that will best accommodate your needs. Remember, sometimes less is more … you do not need high levels of illumination coming from individual fixtures. Instead, use several fixtures at lower wattages for better effect.

Low voltage systems require the use of a transformer to reduce standard 120 V power from your home to 12 V. 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 fixtures x 24.4 watts each = 268.4 total watts).

Generally, the total lamp load should not be less than one-third the transformer’s wattage rating, nor exceed its maximum wattage capacity. If your total wattage is to high, either divide the load between two transformers or use a more powerful transformer.