Buildings VIII/Fenestration Principles—Principles 1 ABSTRACT In this work we discuss the optical behavior of transparent materials, such as colored and colorless glass, as well as the sput- tered and pyrolitic reflective glass types, used in building facades. The optical evaluation of these materials is carried out in differ- ent solar spectrum intervals: ultraviolet, visible-light, and near infrared, and the obtained data are related to thermal and visual comfort. This approach leads to the identification of the ideal glass for warm climates, as in Brazil, which should transmit visible light but not near infrared radiation. Spectrophotometric analysis of the transmitted radiation is performed for different incidence angles, varying from 0° to 80°, and by scanning the solar spectrum, from 300 nm to 2000 nm. At the value of 60° of the incidence angle, the transmission of the solar spectrum is significantly attenuated. These results are important for applications in archi- tecture because data commonly found in the literature are usually related to normal incidence, which very rarely occurs in real situations. The results of this work complement available technical information, allowing a more adequate analysis of the use of the tested glasses. INTRODUCTION Frequently, when designing glazing facades, architects hardly find specific technical data related to radiation trans- mission for different regions of the solar spectrum and differ- ent incidence angles. The data found are usually given for normal incidence of radiation, which is seldom the case for building facades. This work brings up new technical contri- butions to better evaluate buildings in terms of illumination and solar gain. The solar spectrum, which comprises radiation in a range of wavelengths from the near ultraviolet region (wavelength from 300 nm to 380 nm), through visible light (380 nm to 780 nm), to near infrared (780 nm to 2000 nm), is partially trans- mitted through glasses. Transmission can be further attenu- ated with the addition of oxides to the glass composition or with the application of solar control films, resulting in larger absorption and reflection of the solar radiation. Effective solar control can also be achieved by the use of reflective coatings. Increased reflection implies a reduction of transmission. Reduced heat gain can be obtained with low emissivity, or low-e, coatings. A lower emissivity raises reflection of far infrared radiation, which increases the ther- mal insulation. Any surface with an emissivity at or below 0.20 is considered a low-e surface (Johnson 1991). The spectral transmission through glass depends on the chemical composition, color, internal optical absorption coat- ings, and surface characteristics. Usually the available data for light transmission, reflection, and absorption in glasses are given for normal incidence measurements. The amount of energy directly transmitted through transparent materials decreases as the angle of incidence becomes larger than 45°. At 60° the transmitted radiation is significantly reduced and reflection is increased, as shown in Figure 1 (ASHRAE 1997). One of the reasons for the use of glass in windows is to allow the passage of daylight, but glasses are also the cause of heat gain. The glasses used in civil construction may be divided into groups, classified by their transmission, absorp- tion, and reflection coefficients. All types of glass absorb, reflect, and transmit portions of the incident solar radiation. Evaluation of Solar Radiation Transmission Through Transparent Facades Rosana M.Caram, Ph.D. Joaquim Pizzutti Lucila C. Labaki, Ph.D. Eduvaldo P. Sichieri, Ph.D. Rosana M. Caram and Eduvaldo P. Sichieri are with the Department of Architecture and Urbanism, University of São Paulo, Brazil. Joaquim Pizzutti is with the University of Santa Maria, Brazil. Lucila C. Labaki is with the Department of Civil Construction, UNICAMP Campinas, Brazil.