Evaluating White LEDs for Outdoor Landscape Lighting Application (2002)
Light Emitting Diodes (LEDs) are good potential light sources for exterior landscape lighting in terms of ruggedness, efficiency, small size, low voltage, durability, and long life. The goal of this study was to understand the acceptability of different white LEDs, in comparison to popular halogen sources currently for outdoor landscape lighting applications. The application addressed in this study is the exterior of a building and landscape lighting such as along pathways, steps, flowerbeds, and near small shrubs. Two types of white LEDs (down converted phosphor and Red-Blue-Green-RGB) and halogen light source were evaluated in an outdoor landscape setting.
LRC researchers replicated the outdoor nighttime lighting environment of a restaurant exterior. This was done with a scaled model that was partitioned into two symmetrical looking scenes as shown in the picture below. Four types of lighting provided equal luminance levels and light distributions on either side: halogen, white phosphor LEDs, and two white light systems using red-green-blue (RGB) LEDs (low CCT: 3050K and high CCT: 5800). Human subjects rated their preference between lighting conditions in the model, while viewing them side by side.
Specifications of sources used
- The scene lighted by RGB 3050K LEDs followed by the halogens, was most liked and was also found to be most inviting and appropriate for the application. The white phosphor LED had the lowest rating for the above parameters.
- White phosphor LEDs were found to be the brightest.
- The results also indicate that CRI may not be a valid metric for evaluating the color-rendering properties of a light source at low light levels. The RGB 3050K LED with the lowest CRI had the greatest acceptability in this application.
|Result of the scene using RGB 3050K, RGB 5800K, and phosphor white 5800K.