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Vol. 76 (2011) No. 665 P 1229-1234



Two kinds of directional retroreflective materials are manufactured, which are designed to show abrupt change in reflectance at the incident angle (Θ) of around 30 degrees. The measured solar reflectances are 17.7 percent for Θ ≥ 40 deg. and 39.0 percent for Θ ≤ 20 deg. for one type; 54.4 percent and 40.8 percent for the other. Building materials having these kinds of incident angle dependences can be used as cool roofs free of side effect; they can be high-reflective exclusively against summer sunlight, and low-reflective against other light sources, such as, winter sunlight, headlights of cars, and street lights.

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