NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 74 photometric diagram: a diagram that shows the expected spatial distribution of light from a given luminaire. photoperiodism: the physiological reaction of organisms to the length of day or night. photopic vision: vision of the eye under well-lit conditions. In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a higher visual acuity than available with scotopic vision. See visual acuity and scotopic vision. phototaxis: the directional movement of an organism in response to light. The movement may either be towards the light source (positive phototaxis) or away from the light source (negative phototaxis). reflective: capable of physically reflecting light. reflectivity: the fraction of radiant energy that is reflected from a surface. renewable energy: energy derived from resources that are regenerative or that cannot be depleted. Renewable energy resources include wind, solar, biomass, geothermal, and moving water (e.g., dams, tidal bores, ocean current, wave energy devices). retroreflective: a descriptive term for surfaces that reflect light back toward the light source with a minimum scattering of light. scotopic vision: vision of the eye under low light conditions. In the human eye, cone cells are nonfunctional in low light. Scotopic vision is produced exclusively through rod cells. Scotopic vision does not discriminate between colors and has low visual acuity. See visual acuity and photopic vision. skyglow (or sky glow): the brightening of the nighttime sky that results from scattering and reflection of light by moisture and dust particles in the atmosphere. Skyglow is caused by light directed or reflected upwards or sideways and reduces one’s ability to view the night sky. sodium vapor lamp: a gas-discharge lamp that uses sodium in an excited state to produce light. Low-pressure sodium vapor lamps are an energyefficient form of outdoor lighting in which a lamp contains neon gas that lights at a relatively low temperature. As the temperature increases, sodium in the lamp begins to vaporize and creates a monochromatic yellow light. special recreation management area (SRMA): an area designated by the BLM and managed as an administrative unit where the existing or proposed recreation opportunities (e.g., activities, experiences, and benefits derived from those experiences) and recreation setting characteristics are recognized for their unique values, importance, or distinctiveness, especially compared to other areas used for recreation. specular reflection: the reflection of electromagnetic rays without scattering or diffusion. In specular reflection, the angle at which the wave is incident on the reflecting surface is equal to the angle at which it is reflected from that surface. Also known as direct reflection, regular reflection, or mirror reflection. See diffuse reflection. substation: an electrical system used to switch generators, equipment, and circuits or lines in and out of a system. It is also used to change alternating-current voltages from one level to another. A substation consists of one or more transformers and associated switchgear. temporal niche partitioning: the partitioning of various species’ activity periods over time based on varying levels of light. See niche partitioning.
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