NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 72 land use plan: a set of decisions that establish management direction for land within an administrative area, as prescribed under the planning provisions of the Federal Land Policy and Management Act of 1976, as amended (Public Law 94-579; 90 Stat. 2743); a document containing an assimilation of planning decisions developed through the planning process outlined in 43 CFR Part 1600, regardless of the scale at which the decisions were developed. Synonyms include resource management plan and management framework plan. light clutter: a type of light pollution caused by excessive groupings of lights, such as are seen in typical urban environments where there are large numbers of lights of different types. light-emitting diode (LED) lighting: a semiconductor device that emits visible light when an electric current passes through it. light loss factor: a multiplier that is used to predict future performance (maintained illuminance) of a lighting system based on the initial properties of the system. The light loss factor accounts for the decline in lumen output over time. Light loss factor = 1 (initial output of the system) minus expected depreciation. light pollution: any adverse effect of manmade lighting, such as excessive illumination of night skies by artificial light. Light pollution is an undesirable consequence of outdoor lighting that includes such effects as skyglow, light trespass, light clutter, over-illumination, and glare. See astronomical light pollution and ecological light pollution. light spill: see light trespass. light trespass: a type of light pollution in which light is cast where it is not wanted or needed. Also referred to as light spillage or light spill. lighting zone: a zoning system establishing recommended performance standards for lighting for particular areas (IDA-IES 2011). lumen: the unit of measure used to quantify the amount of light produced by a lamp or emitted from a luminaire (as distinct from “watt,” a measure of power consumption). Technically, the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela. See candela. lumen depreciation: the loss of the original light output of a lamp or fixture that occurs over time. luminaire: a complete lighting unit (fixture), consisting of a lamp or lamps and ballast(s) (when applicable), together with the parts designed to distribute the light (reflector, lens, diffuser), to position and protect the lamps, and to connect the lamps to the power supply. It does not include the pole or other mounting hardware. Sometimes referred to as a light fixture. luminance: the intensity of light emitted from a surface per unit area in a given direction. luminescent: emitting light not caused by heat. luminosity: the brightness of a light source of a certain wavelength as it appears to the eye. lux (lx): the SI (International System of Units) unit of illuminance. One lux is one lumen per square meter (lm/m2). 1 lux = 1 lm/m2 = 0.093 footcandles (1 footcandle = 10.76 lux). In photometry, lux is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. See lumen and illuminance. melanopic/photopic ratio (M/P ratio): a metric for evaluating the biological effects of light for humans and most wildlife, by comparing the proportion of melanopic light (light that affects biological function such as circadian effects) to photopic light (light that supports vision) for a given light source. melatonin: a hormone secreted by the pineal gland especially in response to darkness that has been linked to the regulation of circadian rhythms.
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