NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 37 For certain tasks for which accurate color rendition is needed, consider using light with a high color rendering index (CRI). CRI values range from 0 to 100, with 100 showing true colors of objects. Lighting with CRI values at 80 or higher are good. The CRI is unrelated to color temperature. For example, lighting products that provide the same color temperature as 2,700 K may have different CRI values. Correlated color temperature (CCT) or spectral tunable lights offer important opportunities for addressing problems related to light color because they are programmed to adjust color for different tasks or ambient lighting conditions in real time. Theoretically, they could be switched to a brighter and cooler white for specific tasks, and when the task is completed, switched to a dimmer, amber, orange, or red as the default mode where some level of lighting is still needed. Spectral tuning can also be automatically adjusted as human activity decreases, such as during late night hours. 4.5 Use the Minimum Level of Illumination Necessary: Avoid Over-Illumination The purpose of the fifth guiding principle is to use the lowest possible level of light brightness (lumens) that meets an area’s lighting needs; this practice prevents over-illumination. Consider the CRI when accurate color rendition is critical. Over-illumination can make wayfinding and tasks less safe by destroying dark-adapted vision and by causing too much contrast between lit and shadowed areas. It also wastes energy and money, and the excess light may contribute to skyglow, light trespass, and other types of light pollution. Brighter light has greater negative effects on wildlife and human circadian rhythms. Lighting for facilities and outdoor tasks need not exceed the minimum number of luminaires, intensity, and coverage required for safety, basic security, and task requirements. This requires careful design for new lighting systems but can also be achieved for existing lighting systems by simply turning off unneeded lights, installing lights with lower luminance, using dimmers to reduce the luminance of existing lights, or adding/ improving shielding. 4.6 Use Energy-Efficient Lights and Advanced Lighting Controls: Save Energy While Adding Useful Lighting Capabilities The sixth guiding principle encourages the use of energy-efficient lighting and advanced lighting controls. When combined with good lighting design and practices, the use of energy-efficient lights and advanced lighting technology can result in improved lighting performance and reduced effects from artificial light at night, while saving energy and money. Energy-efficient lighting products, such as LEDs, cost less to operate and, if carefully chosen to avoid blue-rich light, can reduce effects on human health, wildlife, and cultural resources. In many situations, new, more efficient lighting pays for itself quickly, because of reduced energy consumption and lower maintenance costs. Advances are not limited to just the lights; a well-designed, shielded luminaire can use a smaller wattage bulb and still be effective. CCT tunable lights can be used to turn off or reduce the luminance (and power consumption) of lighting, and their color can be changed as needed, yielding better lighting performance while minimizing energy use. This 20-acre parking lot is only open for occasional use yet is brightly lit every night.
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