Used for testing the light transmittance of building Windows, suitable for building Windows made of various materials. It includes the transmittance coefficient and color transmission index of the upper part of the skylight and the balcony door, and can detect the transmittance coefficient and color transmission index of the glass curtain wall at the same time. 1. standard of execution GB/T 11976-2015 Graduation and test method of daylighting properties for external windows. 2. Main technical parameters Test items: transmittance T and color transmittance R. The testing device consists of light source room, light source, receiving room, specimen frame and testing instrument. Light room: The inner surface is diffusely reflected with low spectral selectivity and a reflection ratio greater than 0.8 The illuminance on the surface of the specimen is greater than 1000lx, and the illuminance difference at each point is less than 1% The light source room shall be rectangular, with the opening area less than 10% of the indoor surface area light source： Electric light source with continuous spectrum, symmetrical arrangement and light control device are adopted The light source is powered by a stabilized voltage source, and its voltage fluctuation is no more than 0.5% The stability of the light source was checked according to the method described in appendix 1 of jjg247-1994 The light source is specially designed to ensure that no direct light falls on the surface of the specimen Reception room： The inner surface is diffusely reflected with low spectral selectivity and a reflection ratio greater than 0.8 The receiving chamber is a cube, and the opening area is less than 10% of the indoor surface area Specimen box： The thickness of the specimen frame is equal to the actual wall thickness The connection part between the specimen frame and the two-chamber opening is strictly sealed to ensure no light leakage Optical receiver: The optical receiver shall have a V() correction whose spectral response is consistent with the illumination efficiency of the international illumination commission’s light vision spectrum The optical receiver has a cosine corrector, and the optical receiver meets the requirements of the first-level illuminometer specified by JJG245 The optical receiver is uniformly arranged on the periphery and inner side of the opening of the receiving chamber, and the quantity is set according to the size