Credit: Cree Inc.
The same street in Danville, Calif., before HPS streetlights were replaced with LED lights.
Light-emitting diode (LED) technology can save 50% to 80% in energy over high-pressure sodium (HPS) and other traditional streetlights. It can virtually eliminate routine maintenance. It can enhance nighttime visibility. And the diodes don’t contain mercury, offering environmental advantages.
As the technology has advanced, prices have declined, making solutions more affordable than ever. Coupled with increased discussion of successful installations from around the globe, elected officials are asking how to make LED part of their communities.
Here is what you should consider when specifying to maximize performance, value, and savings.
Set sustainable performance goals
It’s easy to get caught up in how much energy and maintenance can be saved, but before that, define a minimum level of illumination (lighting) you want to achieve.
Setting sustainable illumination performance requirements involves defining a desired application life (50,000 hours is common) as well as the lowest light level you are willing to accept from the products being considered over that defined life. Based on a 50,000-hour desired application life, products are evaluated on the performance they provide at 50,000 hours of service rather than initial or day-one performance. This helps ensure that the lowest acceptable light levels occur at 50,000 hours and not before.
Use best industry practices to determine acceptable lighting performance, such as RP-8, the American National Standard Practice for Roadway Lighting. Or perhaps base it on current performance, for example, trying to match existing minimum light levels currently being achieved. Don’t be afraid to ask for help. Reaching out to lighting professionals for assistance is highly recommended and can add significant value to the process.
Then determine required sustainable economic performance. A life cycle cost analysis is critical when evaluating LED streetlights, so set an evaluation timeframe. Typically, the desired application life discussed above is also used here (the 50,000-hour example above would equate to roughly 12 years for most street-lighting applications). Also consider product durability requirements, compliance standards, and warranties to help ensure optimal results.
Specify the system
Once you’ve decided LED is a viable option, check out the U.S. Department of Energy Municipal Solid-State Street Lighting Consortium (http://go.hw.net/tejze) for model specification and financial analysis tools to help find LED systems that will meet your lighting as well as your financial needs.
Credit: Cree Inc.
The City of Danville, Calif., replaced HPS streetlights with LED streetlights manufactured by Cree Inc. The result is improved illumination, as well as energy and maintenance savings.
Their systems specification identifies products that deliver the greatest value while providing some level of sustainable illumination performance. It also characterizes luminaire performance based on site-specific characteristics such as mounting height, pole spacing, number of drive lanes, and required light levels and uniformity.
In addition to mechanical requirements, consider visual product quality, design, ease of installation, manufacturer credibility, service capability, value of the warranty, and the technology available to meet current and planned objectives. Seek products from manufacturers that have a track record of successful installations. Request credible performance data.
Focus beyond L70. This is the point at which the LED chip package loses 30% of its initial output (70% remains). Some people mistakenly think it defines the potential life of the luminaire, but it relates only to its LED chip package. The specific lumen maintenance factor for the product being considered based on ambient temperature and desired application life is what’s important.