Pro Handyman Blog

If you are planning on installing a landscape lighting system you better be ready to do some math. You see, it’s not just about plugging in the system and you have light. No, you need to do some calculations and planning first. The biggest consideration is how large of a transformer you need to buy. You can figure this out by doing some quick math.

I would recommend drawing a road map of where you want lights and what wattage each bulb will be. This is critical, because if you exceed 80% of the transformers capacity you will have problems. So, once you have a list of the fixtures and their bulb wattages, add the watts up so that you come up with a number. That number shouldn’t exceed the 80% rule for the transformer. For example, if you add up the watts of all the light bulbs on your planned system and it comes up to 290 watts and your transformer is rated for 300 watts, you better either upgrade your transformer or decrease the bulb wattage or number of fixtures on your system. A 300 watt transformer should be able to handle 260 watts (300 x 80% = 260).

If it is possible you might want to add fixtures in the future, you are better off buying a larger transformer now, rather than buying two 300 watt transformers later. A larger transformer is cheaper that buying 2 separate transformers.

The pre-packaged landscape light systems you can buy at a home center are good to install right out of the package as they have already considered the 80% rule. Just don’t increase the wattage of the bulbs without doing the calculations.