建筑的环境学chapterthermalcomfortable.ppt

建筑环境学chapterthermalcomfortable Illuminance 照度 Illuminance is the density of luminous flux reaching a surface Unit : lux (lx) 1lx=1lumen/(meter)2 If light is falling a surface at right angles to the surface 提示：照度可直接相加，几个光源同时照射被照面时，其上的照度为单个光源分别存在时的照度的代数和。 照度 单位面积被照面上的光通量 定义式 单位I 等于1lm的光通量均匀分布在1m2被照面上 表示被照面上的光通量密度 * Illuminance 照度 in several different cases Inverse square law of illumination 照度的平方反比定律 The llluminance produced by a point source of light decreases in inverse proportion to the square of the distance from the source. Worked example 6.2 A lamp has a luminous intensity of 1200cd and acts as a point source. Calculate the illuminance produced on surfaces at the following positions a) At 2m distance from the lamp, and b) At 6m distance from the lamp Know: I=1200cd d1=2m and d2=6m, E=? Using E1=1200/22=300lx E2=1200/62=33.33lx 一辐射通量为1W，波长为555nm的光源，其光通量为 lm，如该光源在各个方向上均匀发光，则光源在各个方向上的发光强度为 cd，其正下方2m处水平面的照度为 lx。 Cosine law of illumination照度的余弦定律 light strikes many surfaces at an inclined angle and therefore illuminates larger areas than when it strikes at a right angle. Can be calculated using Angle between direction of flux and the normal d—— distance between source and surface ( m) ——Angle between direction of flux and the normal 毕达哥拉斯定理 以上两个定律适用于点光源 一般当光源尺寸小于至被照面距离的l/5时，即将该光源视为点光源 Worked example 6.3 A lamp acts as a point source with a mean spherical intensity of 1500cd. It is fixed 2m above the centre of a circular table which has a radius of 1.5m. Calculate the illuminance provided at the edge of the table, ignoring reflected light. know: I=1500cd, E=? Using :triangle laws三角形定律 d=2.5m Note: you do not need to know the actual value of the angle in degrees Using 2m 1.5m 2.5m Diffuse reflection 漫反射 Specular reflection 镜面反射 Reflection 反射 Reflectance 反射率 luminous flux reflected from a surface the flux incident upon the surface Worked example 6.4 A point source of light with a lumin