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# TB0005 <br />Fundamentals of Spill Light, Glare, and Sky Glow <br />I. What is spill light? <br />H. How is spill light measured? <br />M. What is glare? <br />IV. How is glare measured? <br />V. What is sky glow? <br />VL How is sky glow measured? <br />I. What is spill light? <br />Spill light is the light that trespasses or "spills" off the intended area and illuminates adjacent property, <br />and it is generally considered as unwanted. If the neighboring property owner is concerned about spill <br />light, steps can be taken to control it. <br />H. How is spill light measured? <br />Spill light is measured in terms of illuminance, for which the units of measure are foot - candles (fc) and <br />lux (lx). <br />It is common for local authorities to place limitations on the amount of spill light that is allowed at a <br />lighted sports facility, and the limits are typically specified either at the property lines of the facility or <br />at a perimeter that is ISO' from the playing field. These limitations may be applied to new or retro -fit <br />lighting installations, and they are often written into the specifications of the project. When developing <br />a lighting design for a project where spill light may be a concern, Musco commonly produces spill light <br />scans showing both horizontal illuminance and max - illuminance at the locations of concern. <br />A. Horizontal spill light readings provide the end user with a bench mark for understanding the <br />amount of illuminance reduction that occurs from the relatively brightly lit sports field to the low <br />illuminance levels at the neighboring property line. Horizontal illuminance can be measured in the <br />field with an illuminance meter, having the lens of the meter parallel with the playing surface. <br />There are limitations in doing field measurements for horizontal spill light: <br />• Generally speaking, a light meter is less accurate .when applying cosine correction to an <br />extreme angle of incident light, as is the case with spill light. <br />• Horizontal light meter readings may be inaccurate at an extreme angle of incidence, unless a <br />level tripod is used, due to sensitivity with holding the meter in a level position. <br />B. Max-illuminance is a reliable measurement for evaluating the quantity of spill light. Often the <br />concern of a neighboring resident is the light on the side of a house or shining through a window. <br />It is relevant to use max - illuminance to quantify such spill light conditions, since max-illuminance <br />is measured in a nearly vertical plane, with the lens of the meter directly facing toward each light <br />bank. When taking field measurements at any particular location, the lens of the meter is pointed <br />directly toward each light bank and panned across all the light banks until the highest illuminance <br />reading is found. <br />lilig. <br />02001, 2003 Musco Ughtlng <br />800 825 6030 <br />Www.musco.com <br />email: lighting @musco.com <br />Page 1 of 5 <br />