Outdoor Landscape Lighting Facts
Most garden lighting is of the "low voltage" variety. That means it can't plug directly into your wall. It also reduces the danger and means you don't need a building permit to install it. If you do want to run standard voltage wiring, you'll need a permit and the help of someone experienced.
The alternative is to use a transformer to convert standard electricity from 120 volts to a manageable 12.
You need to choose the transformer with the correct wattage rating. To determine this, add up the number of watts in the bulbs you plan to use. For example, if your system will have five 20-watt bulbs and a 60 watt bulb, the total wattage will be 5 times 20 plus 60. That's 160 watts total. A 150 watt transformer will power these bulbs just fine, but there's no margin for error. And if you ever choose to add another bulb, you'll need a bigger transformer. So multiply the total wattage of 160 times 1.25 to get 200 watts total. A 200 watt transformer will be the right tool for this task.
On the other end, you don't want a transformer that's under-loaded. This will over-power the bulbs and shorten their lives. A transformer should be powering at least 60% of its capacity to avoid this. So the 200 watt transformer we just mentioned should have at least 120 watts (200 times 0.6) worth of bulbs attached.
Make sure you get a transformer that is weatherproof and IP rated for outdoor use. They can be mounted on a wall or post or even buried underground. A transformer can have more than one cable running from it.
The cables should be buried to protect them from foot traffic, lawn mowers, and the weather. If you are using low voltage lighting, the cables don't need to be buried very deeply since they're not a safety concern. Just put them down far enough that they won't come back up. The cable can run under mulch and over or around fixed structures.
Cables lose voltage as they grow in length. This causes the lights to dim. You want to keep the cable as short as reasonably possible while leaving enough slack for changes of mind. You can avoid voltage loss by using transformers to power lights that are close together, even if they're parts of different designs.
Adding lights to a cable can also cause it to lose voltage. As a rule of thumb, limit yourself to three 20 watt bulbs equally spaced along 30 feet of cable. For higher powered bulbs use a single cable dedicated to that bulb alone.
You can buy reflector lamps with beam angles of 12, 24, 36, and 60 degrees. The lower the angle, the smaller the pool of light created. You can also buy adjustable lamps so that you can experiment with the angle and fine tune it.
Don't forget that the lights can get hot. Handle them with thick gardening gloves or other insulating apparatus.