What Size Transformer Do I Need for Landscape Lighting?
Choosing the correct transformer size is critical to ensuring system reliability, safety compliance and cost efficiency for your landscape lighting projects. Undersized transformers can cause lights to flicker, dim or fail prematurely. Oversized transformers waste energy and increase your upfront installation costs.
Improper sizing can cause overheating, electrical faults and fire hazards. Calculating the correct size will ensure that your installations meet industry safety standards, which are vital for proper liability and insurance purposes.
Understanding Landscape Lighting Transformers
Transformers are the backbone of landscape lighting projects. The electrical device converts standard household voltage (usually 120V) down to a lower, safer voltage (typically 12V or 24V). Using a correctly sized low-voltage transformer for outdoor lights reduces the risk of electrical shock.
It acts as a “power hub” to distribute electricity to all connected lights and accessories. Evenly distributed power ensures uniform brightness and reliable operation across fixtures, minimizes voltage drop and prevents premature equipment failure.
What Are Volt Amps (VA) and Why Do They Matter?
In the LED industry, and specifically in landscape lighting, the term “volts” is frequently mentioned. Volts and amps refer to the amount of energy consumed in an AC circuit, but do not contribute to light output. This is an essential consideration for designing and planning an outdoor lighting system. When calculating VA, it’s important to note that an LED lamp typically draws more energy than what is listed on the lamp. It is crucial to choose the correct size of transformer, and to do that correctly, it is vital to account for VA.
How LED Drivers Affect Power Consumption
Most retrofit LED lamps used for landscape lighting have a small circuit board inside called a driver. This driver accepts 12 volts AC from a transformer and turns this voltage into DC voltage, which is required to light the LED. Now, this rectified voltage goes through a series of small electronic components, which make the LED light up. It gets much more complicated than that, but I won’t get into electrical circuit design.
All the small electronic components consume watts when the voltage passes through the driver. In the case of small retrofit lamps, a small amount of wattage is certainly measurable and necessary to include in your plan. All LED lights have a power factor value usually between 0 and 1. This number can range from 0.5 to 0.9 in most landscape retrofit lamps. The power factor figure is vital because it calculates volt-amps. For example, if you took the apparent power (the wattage listed on a lamp) divided by the power factor, you would get the VA or the real power of the LED lamp.
Though watts and VA are typically terms that are used interchangeably for incandescent or halogen lamps, VA can be slightly higher than wattage, and must be considered as part of your overall calculations.
Calculating Volt Amps for LED Lamps
Below is a quick example of how to calculate the transformer size for landscape lighting using a 4W LED lamp:
4 watts / 0.85 power factor = 4.7 volt amps
In this example, the transformer will see a load of 4.7 volt-amps from a 4W lamp. Most manufacturers have a VA chart available or published on their website to help designers measure the voltage drop and size a transformer correctly.
It is hard to know the actual power factor of every product on the market today. Some products do not show actual specifications for VA. You can use these formulas in the field if you encounter these products. For standard white lights 2200K to 6000K, multiply the face value of the lamp by 1.67. For instance, 4W × 1.67 = 6.68W. This would be the number you would use to calculate how many lamps could be placed on a transformer.
If you are using an RGBW product, multiply the face value by 1.79. This is because some colors will draw more power than white Kelvin temperatures.
When choosing your transformer size, you’ll need to add up the wattage or VA of all lights and accessories you plan to connect, even those of future expansion products. When you’ve calculated that total, you should choose a transformer with a VA rating of 20-30% higher than your total to account for future expansion and for safety.
Planning Ahead for Future Lighting Expansion
It is essential to plan in advance to ensure you can safely add light fixtures to your design over time. For example, when planning to add lights to new trees, you’ll need to determine how much they will grow over the next three to five years, as well as size the cable and transformer to accommodate more wattage and perhaps more fixtures than the original installation. In most cases, the next size up in the transformer is a minor cost in the long run.
Remember, it is always best to confirm the manufacturer’s specifications on VA and actual power draw before you select a transformer.
Find a Brilliance LED Solution for Every Project
Brilliance LED supplies transformers for landscape lighting suitable for retail and commercial markets. Our premium landscape light transformer solutions are low-voltage options that increase safety, add flexibility, are easy to install and have smartphone integration capabilities. Take a look at our selection of Brilliance LED transformers and become a distributor today.
About the Author
Kevin Smith is the national technical support and trainer at Brilliance LED LLC, Carefree, Arizona, and can be reached via email.
The Right Transformer for the Job by Kevin Smith, National Technical Support and Trainer at Brilliance, was initially published in the Night Lighting column on Irrigation and Lighting’s website. For more information about Irrigation & Lighting Magazine, visit irrigationandlighting.org.
