Determination of the Reflection Factor of Walls, Floors, and Ceilings.

For interior lighting calculations the reflectances of the room surfaces must be known. The relevant quantity in this case is the reflectance for diffuse illumination of the surface rho dif. This reflectance can be measured correctly with the aid of a measuring device with an integrating sphere. In many cases reflectance samples with different colors and known reflectances are used in order to get the necessary values of the reflectances of the room surfaces by a visual match. Sometimes the reflectances are estimated by experienced people. It has been investigated which errors are to be expected if the visual match method or the estimation method is applied and to which extent the accuracy of the lighting design calculations can be influenced by incorrect reflectance values. It is shown that errors up to 20% and more in the room illuminance efficiency are possible if the incorrect reflectance are used.