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One Cool Photo Says a Lot About Your LED Streetlights

November 06, 2014
photometric design photo   

One picture can tell so much about upgrading to LED streetlights – especially when it’s a photometric calculation (left). The name sounds fancy, but its purpose is very simple: to show you what energy experts see and what they expect your streets will look like under LED street lights.

The first step in producing this image is taking a field survey of your city’s entire lighting system. This survey charts every one of your streetlights onto a map along with data identifying its energy use, positioning and many more details used to identify the most energy efficient lighting upgrade using LEDs. Check with your LED upgrade service provider to compare what data they will collect and compare in this step – not all reports are alike.


  • A majority of today’s streetlight poles were erected to carry electricity, not lights. The lights were an add-on to a conveniently high street-side perch. This means the light was placed based on where the pole was, not where the light was needed.
  • Even if the pole was designed for a streetlight, it was designed for High Intensity Discharge lights – a technology 20 to 30 years old.
  • When lighting experts measure which LED fixture is the best fit on that old pole, almost every time they find the same area can be better lit with an LED using less wattage.
  • The way we use our roads today has also changed in the past 20 to 30 years. Roads may be wider and carry more traffic or pedestrians than they did when those old lights first went up. It’s important to upgrade your lighting to keep up with the updated use of each road.

Putting Data to Work

  • First, we chart where the beams of each LED will touch the street on a luminance map (right). The black numbers lined up throughout the intersection represent how much light the fixtures will cast on each charted area.
  luminance image
  • Based on industry standards and calculated measures, lighting technicians identify the best fixture for each pole to evenly cover the road for the way it’s used today. Each area circled in red and each measurement in black helps ensure the most complete coverage possible.

What You See

  • Now it’s time to create our photometric calculation. Using measurements from the luminance map, colors are inserted to allow you to see the end result of the data collection, the analysis, the energy-efficiency measures, and the testing of light levels.
  • A city or town should expect a variety of photometric calculations from your LED service provider featuring different types of roads (quiet residential, busy downtown, arterial throughways, etc.).


An LED streetlight upgrade is a major investment for any municipality and deserves in-depth analysis to explain your projected energy savings, your project cost payback and show the lighting you can expect on your streets. Attention to detail and data in this pre-project analysis can help you realize better results from your upgrade (the average municipality saves 50 to 70% in energy consumption and energy cost when switching to LEDs).   When these early steps are done well, project outcomes are better.

When you begin researching the savings an LED upgrade can deliver for you, ask how these images will be created for you and what data they will provide so you can play an informed role in your LED decision.

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