NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 71 contrast: difference in luminance or color that makes an object (or its representation in an image or display) distinguishable. Contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view. See luminance, color, and grayscale contrast. correlated color temperature (CCT): a specification of the color appearance of the light emitted by a lamp, relating its color to the color of light from a reference source when heated to a particular temperature, measured in degrees Kelvin (K). crepuscular: done, occurring, or active during twilight. diffuse reflection: reflection of light from a surface such that a ray incident on the surface is scattered at many angles rather than at just one angle as in the case of specular reflection. See specular reflection. diurnal: done, occurring, or active during the day. ecological light pollution: light pollution that alters natural light regimes in terrestrial and aquatic ecosystems. See light pollution and astronomical light pollution. effect: a change which is the result of an action or other cause. Effects may be positive, negative, or neutral. Synonymous with impact. See impact. forward throw asymmetric luminaire: a luminaire with a light distribution pattern that casts light in an oval pattern offset from the pole such that there is minimal backlighting. fully shielded luminaire: a type of luminaire that emits no uplight and limits glare between 80° and 90° from the ground. Fully shielded luminaires have a light distribution in which no light is cast at or above an angle of 90° above nadir (straight down) with a U0 rating per IES TM-15-20 (IES 2020). See luminaire and unshielded luminaire. glare: the sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted, which causes annoyance, discomfort, or temporary loss in visual performance and visibility. grayscale: a range of monochromatic shades from black to white. A grayscale image contains only shades of gray and no color. grayscale contrast: the amount of grayscale differentiation that exists between various image features in an image. Images having a higher grayscale contrast level generally display a greater degree of grayscale variation than those of lower contrast. See grayscale and contrast. hazard navigation lighting: the illumination of an object for increased conspicuity to ensure the safety of air or water navigation, or the lighting equipment used to achieve this purpose. horizontal illuminance: illuminance measured on a horizontal plane (i.e., the amount of light that lands on a horizontal surface), such as a sidewalk or flat ground. See illuminance. illuminance: a measurement of the amount of light falling onto (illuminating) and spreading over a given surface area. Illuminance is a measure calculated at a surface, such as the ground (horizontal illuminance) or a wall (vertical illuminance). The metric (SI) measure of illuminance is the lux (footcandle in the Imperial System). Also known as incident light or brightness. See lux and lumen. impact: a change which is the result of an action or other cause. Synonymous with effect. See effect.
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