NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 62 5.5.1 Use “Night Sky Friendly” NarrowSpectrum Amber, Orange, or Red Light Sources Unless tasks require highly accurate color rendition, use “night sky friendly” light sources that emit narrow-spectrum, long-wavelength (greater than 560 nm) light, such as amber, orange, or red color temperatures (< 3,000 K). These lights are likely to have fewer ecological and human health effects compared with broader spectrum or “whiter” light sources such as many LEDs and metal halide lamps (Longcore et al. 2018). Broad spectrum, bluish-white lighting or lighting rich in UV light (> 3,000 K) are not recommended for use in permanent outdoor lighting. If safety-related lighting requirements call for accurate color rendition that precludes the use of narrow-spectrum, long-wavelength light sources, then broad-spectrum light sources with a correlated color temperature (CCT) of 2,200 K or below can be used, in combination with lighting controls such as motion sensors, timers, dimmers, etc. Notes: Filters, gels, or lenses should not be used to manipulate color in light sources. Narrowspectrum amber, orange, or red light sources typically have relatively poor color rendition (i.e., they have a low CRI). Narrow-spectrum lighting may cost more than broad-spectrum lighting. Exercise care when selecting LEDs, and use them in properly designed luminaires that limit light trespass. Avoid increasing light levels beyond minimum levels required for safety. 5.5.2 Use Tunable CCT Lighting to Adjust Color of Light Sources When and where appropriate, use tunable correlated color temperature (CCT) lighting to adjust the color of light sources for task requirements (to reduce spectroscopy effects, see Section 3.3.3). Tunable CCT lighting allows changing the color properties of the light source to suit the task at hand. For example, change the light color when performing a task requiring accurate color rendition, and then change it back to a more wildlife friendly color afterwards. When used with other lighting controls such as dimmers and timers, tunable CCT lighting reduces effects on wildlife and saves energy (Council on Science and Public Health 2016). Notes: Tunable CCT lighting costs more than conventional lighting and requires expertise to select and program correctly. CCT technology with sufficiently low CCT (2,200 K or less) is preferable. A method for rapid assessment of lamp spectra to quantify ecological effects of outdoor lighting was developed by Longcore et al. (2018), though it is not comprehensive. The pedestrian path to the Lowell Observatory uses “night sky friendly” amber path lighting. Claudia Angerer This set of photos of an indoor lamp shows how tunable CCT lighting controls can be used to alter the color spectrum of a light source on demand.
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