LEDs’ advantages/challenges for municipal lighting

LEDs’ advantages/challenges for municipal lighting

The local-government programs are focusing on the costs of lighting, which can account for 20% of the energy budget

BY MARK MCCLEAR
Cree, Durham, NC
http://www.cree.com

and DAN HOWE
City of Raleigh, Raleigh, NC
http://www.raleigh-nc.org

For most local governments, energy savings is currently a key strategic goal, encompassing new initiatives in electricity savings and generation, fossil-fuel conservation, and “green” building practices. One major focus for these programs is reducing energy costs associated with lighting, which accounts for roughly 20% of electric energy demand in a typical municipal operating budget.

LED streetlights brighten a Raleigh, NC, public area. (Photo: Beta LED, Sturtevant, WI)

In addition to the cost of energy, maintaining traditional lighting adds significant expenses to the local government’s operating tally. It costs a minimum of $50 to $60 to change a light bulb in an exterior application, and can cost as much as several hundred or even thousands of dollars when the fully loaded cost of maintenance (labor, benefits, equipment rental or depreciation, replacement parts, inventory storage, lost operating time) is taken into account. For example, in an indoor aquatics center, changing a typical metal-halide lamp over the pool requires that scaffolding be erected and the entire pool be shut down for one or more days.

LEDs’ advantages

LED lighting technologies can dramatically reduce the need for maintenance. The City of Raleigh, NC, is nearing 95% utilization of LED traffic signals, not because of a 70% or greater energy savings, but primarily because of maintenance savings. With a 100% LED signal system, a 24/7 on-call repair function will only be needed for total electrical failure at any intersection; the lights themselves contain hundreds of LEDs, which makes safety failures (loss of a signal “eye”) virtually impossible as long as the fixture is energized.

By the time a municipality would need to perform the first maintenance call on its LED streetlamps (after about 10 years of 12 hour/day operation), the fixture should have paid for itself in maintenance savings, as conventional metal-halide bulbs will have had to be replaced about 8 times, or every 2.5 years. Over a 10-year period, the cities or power companies that own these fixtures could save approximately $400 per pole. New York City, which has about 300,000 streetlamps, could conceivably save $120 million over a decade.

LED public streetlighting holds great promise, not only because of the energy and maintenance savings, but because of LED technology’s unique characteristics:

• Able to easily dim or raise light level based on ambient conditions

• Directional quality of the light, which more effectively casts light where it is needed without spillover, and

• Able to customize color temperature in different settings.

Further, public streetlighting is a major source of “light pollution” (unwanted excess night lighting) in municipal areas, and LEDs could be a simple solution to this problem.

Done well, lighting is “invisible” — there’s no reason to think about it, it’s just there. LED lighting should be no different — in light color, quality, and stability — and should be at least on par with existing lighting technologies. Until the last year or so, that requirement was a hurdle to widespread adoption.

Challenges

To make an LED installation bright enough, so many LEDs were necessary that the cost was prohibitive. And the color of the white light (“warm” white LEDS were not available until mid-2007) made the light less than desirable for indoor applications. But with significant increases in brightness and other aspects of the LEDs’ performance, the ability to rival the light quality of existing technologies for a reasonable cost is no longer impossible.

Delivering the above performance places two constraints on suppliers: they’ve got to get the cost/value right, and they have to have quality. If cost/value is poor, LED lighting will never move beyond demo sites into widespread adoption, particularly in municipal applications. The same holds true for poor quality LEDs—not only are the LED supplier’s and fixture company’s reputations at risk, but the municipality itself loses the buy-in of its taxpayers and further conversion will most likely be abandoned.

Municipal acceptance of LED technology is hampered by the competition for capital. Because of their initial price, LED lighting solutions have to compete with other important municipal priorities (streets, parks, utility projects, equipment) for capital in both new applications and retrofit situations.

Dramatic changes in levels of acceptance in municipal settings can be made if the cost of utilizing LEDs is moved over to the operating rather than capital budgets, through low- or no-interest financing, or through leasing arrangements that amortize the initial capital cost over the life cycle of the fixture. For many outdoor applications (area lighting, decorative lighting, parking decks, decorative streetlighting) the life cycle return on investment is already there for LEDs. The capital commitment, however, is challenging for local governments, hampering broader acceptance.

Until now, concerns about excessive cost have made the case for remaining with traditional lighting technologies in most municipal applications, as opposed to migrating to LED solutions. Recent advancements in LED technology, however, have addressed these concerns.

Meeting the challenges

Cost and value are created by addressing three main economic levers: initial fixture cost, fixture energy consumption, and maintenance costs.

Initial fixture cost is addressed at an LED component level by making the LEDs bright – the brighter the better. Typical outdoor luminaires, for example, can deliver more than 10,000 lumens. To generate 10,000 lm would require around 100 of the brightest LEDs currently available (see table at left). Lower output LEDs are also available. If lower output LEDs are selected, the LED array could balloon to more than 180 LEDs.

But as the number of LEDs increases, everything goes in the wrong direction that is, in addition to increased LED cost, the physical size and weight of the luminaire are driven up, wind resistance gets worse, and driver cost and power consumption are negatively impacted.

Higher brightness LEDs drive the cost of the fixture down and help to set the life cycle payback time. In Fig. 1 , the luminaire’s initial cost is the starting point for the graphs on the left as is shown on the y-axis. The payback time is the point where the graphs cross each other.

Energy consumption is the second lever. Like all lighting components, the efficacy (efficiency of converting electrical energy into visible light) is measured in lumens output per watt input (lm/W, or LPW). The LPW of the system is depicted in Fig. 1 as the slope of the two lines. In this case, very efficient LEDs were selected so the slope of the LED line energy cost is less steep. Over the life cycle of the luminaire, this yields tangible savings to the City at a 12-hour/day use; energy savings for 24 hours is even more dramatic.

Fig. 1. While the initial cost of an LED fixture may be higher, it’s higher energy efficiency and longer lifetime make it a more cost-effective choice.

Finally, there is the maintenance cost. Maintenance costs vary greatly depending upon application. For many indoor fixtures, changing a light bulb is a hassle, but it does not cost much money to do it. For outdoor fixtures, the cost can be quite high. The discontinuities in the blue line of Fig. 1 are re-lamping events for the metal halide fixture. In a well-designed system, lighting-class LEDs can last 50,000 hours or more, thus avoiding maintenance events for more than 11 years at a 12-hour/day rate.

Together, bright lighting-class LEDs deliver the best energy efficiency and longest maintenance-free lifetime of any known artificial light source which can spur the widespread adoption of the technology for municipal applications.

It’s happening right now

For many local governments, LEDs are not the technology of the future they are being implemented now. And there are plans for larger installations across cities around the world.

For Raleigh, parking deck lighting has been particularly successful. The city recently installed 544 LED fixtures (manufactured by Beta Lighting, Sturtevant, WI) in a 920-space underground parking deck. Owner satisfaction is high with these fixtures: they have remarkable light uniformity, reduce energy demand in excess of 60% over the traditional fixtures they replaced, and are designed with removable “light bars” that allow phased replacement of LED arrays as luminescence drops over time.

In addition, a survey showed that respondents who perceived the garage as “very safe” increased by 76%. This is just one example of how LED lighting can boost quality of life and save energy/maintenance costs. ■