Cooper addresses advantages and challenges in outdoor SSL

Nov. 16, 2010
A recent conference presentation examined the opportunity, challenges, and advantages that LED-based SSL faces in outdoor applications.

Outdoor lighting represents perhaps the biggest growth market for LED-based lights in terms of the general illumination area, and Cooper Lighting addressed that opportunity at the recent LEDs 2010 Conference in San Diego, California. The presentation projected a 120% compound annual growth rate (CAGR) for solid-state lighting (SSL) in outdoor area applications and significant advantages in delivering lumens to a target zone.

John Gach, Cooper’s regional sales manager for advanced technologies, presented “Outdoor LED Applications: Growth & Challenges.” He highlighted the opportunities for outdoor SSL along with the obstacles to adoption and the advantages the technology can deliver.

Early on in the talk Gach presented a table of growth forecast figures segmented by application. While the CAGR for SSL in general illumination in aggregate is 37% through 2012, Gach pointed out that the CAGR for outdoor area lighting is 120% in the same time period. Other segments that we hear about often in relation to SSL such as retail, industrial, and architectural come in at 50% CAGR and below.

Energy savings and the corresponding reduction in greenhouse gases are the primary driver toward SSL in outdoor applications. We’ll get to some specifics in terms of energy savings a bit later, but consider the environmental impact. According to Gach, replacing 30 250W metal halide lights with SSL alternatives can reduce greenhouse gas emissions by more than 250,000 pounds over ten years. The reduction is primarily in carbon dioxide but there are also significant reductions in methane and nitrous oxide.

A complex ecosystem

There are of course well know challenges to broad deployment of SSL. Gach pointed out the complexity of the ecosystem as a challenge. Indeed you have the normal product design and manufacturing chain that starts with LED chips and flows through to the luminaire maker, but SSL requires a much more complicated set of driver electronics relative to legacy lighting technologies. Moreover you have a broad set of stakeholders including government agencies, standards bodies, independent testing labs, utilities, municipalities involved in the outdoor lighting segment.

Parking lot with legacy HID lights

The cost of LED-based luminaires is also an issue, but prices are dropping and the payback period in outdoor applications is reasonable. In a recent article on the Street and Area Lighting Conference, we noted that the City of Los Angeles is projecting payback in less than six years – down from an earlier projection of seven years.

Gach believes that a thorough evaluation of total cost of ownership (TCO) shows LEDs to be viable cost wise. He pointed out that the full TCO picture must include the details of the outdoor lighting layout along with the projected energy and maintenance savings.

LED retrofit improves uniformity

The key point in Gach’s presentation on TCO was that lumens per watt (LPW) is alone a poor way to judge or compare LED lights relative to legacy alternatives. While LEDs can offer an LPW advantage, there are additional factors that can compound the advantages of LED technology. Among others, Gach noted target zone efficiency, uniformity, and BUG (backlight, uplight, and glare) characteristics as important.

Target zone efficiency

To illustrate the target zone efficiency and uniformity issues, Gach presented a comparison of a legacy reflector-based HID luminaire design with an LED approach based on individual TIR (total internal reflection) optics for each LED. According to Gach, 70% of the light in the HID design is not aimed. In comparison, the TIR approach aims 100% of the LED light.

The result according to Gach is far superior lighting performance delivered with fewer total lumens. To back up that claim, Gach presented a case study that detailed before and after lighting performance at a parking lot that was retrofitted with Cooper SSL luminaires.

The HID installation has a system power of 458W per light while the LED retrofit lamps had a system power of 309W per light. Still the LEDs delivered 2.53-foot-candle (FC) average illuminance compared to 1.41 for the legacy lights. Moreover the maximum-to-minimum illuminance ratio was 16.53 for the legacy lights and 2.93 for the LEDs. Clearly the LEDs are more uniform and you can see that in the nearby photos of the installation.

Gach also presented a detailed comparison of HID and LED luminaires to further make the point as he said, “Not all lumens are created equal – know your application.” The comparison was centered on a 22,000-lm HID luminaire and an 11,000-lm LED luminaire. The comparison assumed a 70% optical efficiency for the HID luminaire and 100% for the LED luminaire. Gach claims that the LED alternative delivers 76% of the available light as street-side lumens while the HID luminaire delivers only 65% street-side lumens. Gach further discussed lumen depreciation and even how dirt affects the two different designs coming up with what he called a light loss factor. The conclusion is the 11,000-lm SSL luminaire is superior according to Gach, in terms of lumens delivered on target over the life of the product.