FIGURE 5.1 Subjective lighting survey used by the city of San Jose, California. SOURCE: Clanton and Associates and VTTI (2010).

Directional Distribution

SSL has unique uni-directional distribution characteristics, providing excellent beam control and allowing the fabrication of luminaires that are ideal for long-distance light distributions. For instance, an entire building façade can be grazed with luminaires located at one level. Accent lighting in retail stores can produce high-quality illumination with little energy. SSL has the potential to put light where it is needed with minimal light spillage, but without appropriate optics it can exhibit a sharp cutoff in illuminance with an abrupt termination of the lighted area. For instance, without appropriate optics roadway lighting may not light the adjacent sidewalks. This attribute of SSL emitters may also make for difficulties in the development of omnidirectional lamps replacements for fluorescent and incandescent lamps. In the future this problem could be solved by proper optical designs.

Cool Beam

Because the LED does not emit infrared light as does an incandescent lamp, the beam of light is cool. This makes it ideal for reducing heat on retail products and art work and in other heat sensitive applications. SSLs based on LEDs are currently used in museums (e.g., in Portland, Oregon) and in refrigerated display cases (e.g., Albertsons Grocery in Eugene, Oregon) (DOE, 2012a). Newer domestic refrigerators are also using LEDs for interior lights.

Color Characteristics

SSL has the potential for superior chromaticity and color rendering. As discussed in Chapters 1 and 3, the spectral output of SSL products can be tuned to create virtually any desired chromaticity. This is required in all applications where the users typically compare the lighting color to recognizable sources such as daylight or an incandescent lamp.

In addition to achieving excellent color rendering, some SSL sources can create desirable effects, such as increasing the saturation of object colors. Opportunities exist to select spectral distributions for specific applications, such as rendering artwork, or narrow spectral distribution, such as amber LED (i.e., LED lights without the blue component) for lighting beach boardwalks near turtle hatching areas where young turtles are at risk because they are attracted to blue light similar to the ocean effervescence (Longcore and Rich, 2005).

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