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In lighting design, the lumen method, (also called zonal cavity method), is a simplified method to calculate the light level in a room. The method is a series of calculations that uses horizontal illuminance criteria to establish a uniform luminaire layout in a space. In its simplest form, the lumen method is merely the total number of lumens available in a room divided by the area of the room. In order to perform this calculation, many factors, coefficients, lamp lumen data and other quantities must be gathered. Despite the scientific impression of the lumen method equations, there are inaccuracies and assumptions built into the method. Therefore, the lumen method should not typically be used as a standalone, final solution; it should be used as a tool in particularly uniform settings of lighting design if a simple, rough technique of illuminance quantification is desired.〔Steffy, LC, IES, FIALD, Gary 1963. ''Architectural Lighting Design, 2nd edition'' John Wiley & Sons, Inc., New York〕 ==Light loss factors== Light loss factors (LLF) are the factors that need to be considered when calculating the Lumen Method. The most important factors to be considered are: # Lamp Lumen Depreciation (LLD): Lamp lumen depreciation values reflect the overall performance of a lamp over its life. LLD = (mean lumens/rated lumens) Those values can be found from the lamp manufacturer data # Ballast Factor (BF): Compares the ratio of light output of a lamp working by a specific ballast to the light output of the same lamp working by a standard reference ballast. The BF is given in the ballast manufacturer data. # Luminaire Dirt Depreciation (LDD): It is the light loss prior to cleaning dust. LDD is estimated from tables in IESNA Lighting handbook. # Room Surface Dirt Depreciation (RSDD): This value accounts for dirt or dust that accumulates on all of the room surfaces — especially on the upper walls and ceiling. RSDD is also estimated from handbook tables. The product of all these factors is the light loss factor (LLF) which then is used in the Average Illuminance equation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lumen method」の詳細全文を読む スポンサード リンク
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