Outdoor Lighting Are the homeowners you’re working with considering a landscape lighting system for their residence? We think that’s a superb idea! Now, are you trying to help them do their research and provide them with accurate information so they can be informed buyers? Well, that’s an even better idea! In this blog, we’ll help you master the complicated math used to determine the energy cost of any lighting project you do using LED technology. This may help decide the project’s scope—whether you light just the front of their home, for instance, or splurge and light both the front and back of their home. But, before we jump right in, let’s discuss the number of fixtures that will be required to complete the project successfully. The amount of fixtures needed varies depending on the grandeur of the landscape package (how elaborate the landscape design is) and the scope of the lighting project (how extensive the homeowner would like the lighting project to be.)

How Many Fixtures Do I Need to Light My House?

Generally speaking, 12 to 15 fixtures are used to light a home that is about 2,500 square feet. This 12- to 15-fixture system will achieve three main goals for any quality lighting system: increase the usability, beauty, and safety of a property. This outdoor lighting system will include safety-enhancing path lights along the walkway from the driveway to the entrance of the home; path lights will also be used to beautify flower beds along this route; uplights will graze the facade of the home to further enhance its beauty; and spotlights will illuminate focal points around the front of the home such as large trees. About 25 to 30 fixtures can be used for two primary of landscape lighting scenarios—either to light the front of a 4,000-square-foot home, employing the same design theory as mentioned above, or to light the front and back of a 2,500-foot home. The lighting of this homeowner’s backyard or private space would likely focus on lighting entertainment spaces such as the patio or pool deck area—unless the back of the home offers beautiful brick, stone, or stucco sides, which we would then recommend incorporating this feature in the overall design. A 50-fixture system would likely be used to light the front and back of a 4,000-square-foot home. Again, this all depends on the scope of the project and landscape package, but we think it’s a pretty fair estimate.

Updating Your Outdoor Lighting Vocabulary

Outdoor Lighting In order for a homeowner to truly comprehend how to calculate the energy cost of lighting his or her home with a landscape lighting system, a few terms and averages must first be understood. First, because we are dealing with LED lighting, the homeowner must learn what a “VA” or volt ampere is. This is the term of measurement used for LED lighting. It is identical to “watts,” however, when referring to LED measurement, it’s known as a volt ampere. The second is wire resistance. When electricity is being pushed through a wire, it requires more power over longer distances to get delivered to its final destination. This is known as wire resistance. Thirdly, a typical light uses an average of 5 VAs or watts per fixture. And finally, try to digest Ohm’s Law of Power: Amps = Watts/Volts Watts = Amps x Volts Volts = Watts/Amps Example: 8.33 Amps = 100 Watts/12 Volts

What’s the Energy Cost to Light the Outside of My Home?

Outdoor Lighting Now that the homeowner understands these terms and concepts, we can explain the formula used to calculate the energy cost for his or her outdoor lighting system. Let’s use the example of the 15-light fixtures used to light the front of a 2,500-square-foot home.

  1. Multiple the number of light fixtures in the system (15 fixtures) by the average VAs per fixture (5 VAs): 15 x 5 = 75 VA.
  2. Now add 15 percent for wire resistance: 75 VA x .15 = 86.25 VA
  3. Divide the VA per second by 1,000: 86.25/1000 = .0825
  4. Multiply your answer by the electrical rate in kilowatt hours (Kwh) to determine the cost per hour to run the system. Let’s say it’s 15 cents per Kwh: .0825 x .15 = .012
  5. Multiple your answer by the average number of hours the lights will be on each night: .012 x 5 hours = .062
  6. Multiple that number by 7 days a week: .062 x 7 = .433
  7. Then multiply that number by 52 weeks: .433 x 52 = $22.50
  8. The average cost to light a 15-light fixture system for one year is $22.50.

Using that same formula, a homeowner can deduce that the average annual energy cost for a 30-fixture system is $47 and the average annual energy cost for a 50-fixture system is $78.50. It’s a little complicated, but this formula can be used to see how much money homeowners want to spend in energy costs each year, and therefore many fixtures they may elect to use to light their home.