for the short wavelength components of metal halide and fluorescent lighting. These concerns include photobiological effects and increased skyglow2 (IDA, 2010; Wright, 2011). These effects are most pronounced when lighting is energized all night long.
FINDING: LED white light products produce light in spectral regions that may create environmental and health concerns. These concerns should be recognized in the design and application of LED luminaires.
The long life promised by SSL luminaires has the potential to reduce maintenance, offering not only replacement savings, but also higher reliability. However, SSLs typically do not burn out, but only reduce their light output. So in some applications there may be a liability risk if the SSL is functioning but not producing the expected luminosity. Reduced light output occurred in the past with mercury vapor lighting.
Outdoor SSL luminaires may be dimmed if adaptive standards were to be applied. Adaptive standards are the practice of reducing lighting levels during periods of low activity, such as in the middle of the night when many establishments are closed. This practice is very popular in Europe and is now being introduced into North America through recommendations of the Illuminating Engineering Society (IES) (IES and IDA, 2011). Adoption of such practices would provide communities and property owners the flexibility to reduce lighting levels during periods of low activity, or during peak demand periods, thus saving energy.
Several cities, such as New York City, San Francisco, Oakland, San Jose, and others have performed extensive LED street lighting demonstration projects (DOE, 2012a) as part of the U.S. Department of Energy’s GATEWAY demonstration program.3 In all of these projects, the predicted and measured energy use and maintenance are lower than for conventional lighting, but illuminance levels are also lower compared to existing HPS street lighting. Additional added benefits include reductions in sky glow and light spillage. Some cities, such as San Jose (Figure 5.1) and Anchorage, conducted controlled public surveys to obtain community feedback on the LED street lighting (Clanton and Associates and VTTI, 2009, 2010). The public preferred the warmer color temperature LED, even at lower lighting levels, compared to the existing higher wattage low pressure sodium (LPS) and HPS street lighting (Gibbons and Clanton, 2011).
FINDING: Exterior lighting is a prime candidate for early adoption of SSL because of the lower lighting levels required in such applications and the optical control, long life, and dimmability characteristics of SSL.
While some of the advantages of SSL are immediately obvious, others are still only possibilities. As new technologies and luminaires are developed, new applications will also emerge, leading to unexpected opportunities in lighting design. Current SSLs offer small size, ease of control, uni-directional light, cool beam, superior color, low energy use, and long life. OLEDs promise entirely new form factors, a prospect that opens up a whole new realm of possible applications. Also, because of control compatibility, SSL can further reduce energy through dimming strategies.
The compact size of the SSL modules offers opportunities to put lighting in areas that previously had restricted luminaire size. But the challenge of managing the heat generated by the LED has prevented a desired reduction in the size of the light source needed for high lumen output. As modules become more efficacious, the size can shrink even more. Shrinking size will allow more opportunities for replacement of additional types of lamps such as high-output MR-16 lamps (see Chapter 1). The MR-16 is an important lamp for retail, hospitality, and residential applications.
SSL products have instant on and off operation without the requirement for a warm-up time, an attribute that is in contrast to that of HID and CFLs. With a dimmable driver, SSL products can be dimmed over a wide range of luminous flux in a smooth manner. Dimming below 10 percent is only available with a select number of drivers but is desirable (see Chapter 4). Smooth dimming is also available with some SSL screw-in incandescent replacement lamps. The appropriate choice of dimmers and drivers for SSL will enable control compatibility, which is critical for intelligent energy control systems.
Some control systems can change the color of light by varying the intensity of different colored LEDs in a red, green, blue system (i.e., one which produces white light by combining red-, green-, and blue-component LEDs). These are currently used mainly in special effects lighting, but have the potential for applications in commercial and highend residential markets. For example, retail venues might wish to vary the color of light in a display to emphasize a product’s features.
2Skyglow is the result of blue light being absorbed or scattered in the atmosphere resulting in a loss of visibility of the night sky, which is of special concern to the astronomy community.
3 DOE GATEWAY demonstrations have the objective to showcase LED products for general illumination. DOE publishes detailed reports and briefs on completed projects. The reports include analysis of data collected, projected energy savings, payback analysis, and user feedback. Adapted from http://www1.eere.energy.gov/buildings/ssl/gatewaydemos.html.