Lighting Practices for Isolated Rural Intersections (2022)

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42 Glossary of Technical Terms This appendix lists common terms related to roadway lighting and intersection traffic control that may not be familiar to all readers. In some cases, more than one term can be used to refer to the same concept. This appendix is not a comprehensive glossary of all terms associated with roadway lighting; refer to IES (2017b) for a detailed resource. Adaptive Lighting The use of different light levels throughout different parts of the night to account for higher or lower levels of traffic and pedestrian use. Beacon A type of light source used along the road, usually flashing, that serves as a warning or indi- cator. Not to be confused with beacon lighting. Beacon Lighting An alternative term for delineation lighting. BUG Rating A system to describe the spatial distribution of light output from a roadway luminaire. “B” refers to backlight behind the luminaire that could produce unwanted light onto adjacent properties (see light trespass). “U” refers to upward light that can contribute to sky glow. “G” refers to light at high angles from below the luminaire that can contribute to glare. Correlated Color Temperature (CCT) A term that describes the color appearance of a white light source in comparison to a black- body radiator heated to a specific temperature in kelvins (K). A low CCT (up to 3,000 K) is yellowish-white or “warm white” in appearance and a high CCT (5,000 K or greater) is bluish- white or “cool white” in appearance; intermediate CCT values appear neutral white. Cutoff A characteristic of a roadway luminaire’s spatial distribution that refers to its intensity at high angles from below the luminaire. A P P E N D I X A

Glossary of Technical Terms 43   Delineation Lighting The use of a roadway luminaire, often with low wattage or light output, that may illuminate objects along the road but primarily is used to provide a visual cue to drivers at night that an intersection or other conflict location is present. The intent is for the luminaire itself to be seen by drivers. Also referred to as beacon lighting or destination lighting. Destination Lighting An alternative term for delineation lighting. Illuminance The units of footcandles or lux (10 lux is approximately 1 footcandle) that describes the amount of light falling onto a surface such as a roadway. Intersection Conflict Warning System A system that provides visual warnings to drivers at or approaching a rural intersection of the presence of potentially conflicting vehicles on the intersecting roadway. Light Pollution The unwanted effects of outdoor lighting at night, including increased sky glow, light trespass onto nearby properties, and glare. Light Trespass Illumination from the roadway and other outdoor lighting systems that falls onto adjacent properties but is not wanted by the occupants of those properties. Luminance The units of candelas per square meter (cd/m2) that describe, very approximately, the bright- ness of an illuminated surface in the direction of the viewer. Uniformity A way to quantify the ratio between the maximum illuminance on the road from a lighting system and the minimum illuminance. More uniform lighting has a lower uniformity ratio. Veiling Luminance A quantitative measure of the amount of glare that can be produced by a roadway luminaire to a driver located 83 meters away.