PROBLEM TO BE SOLVED: To obtain a coating material which is used for a field crop-culturing green house built or set using transparent materials such as plastic films or glass plates, aims at the improvement of an environment for the field crops placed in the green house, and has constant light-absorbing effect in a constant thickness, and to provide a method for coating the coating material. SOLUTION: A stock solution capable of being diluted with water is produced by compounding inorganic particles having a <=0.1μm particle diameter colloid region, a light absorbent in an amount capable of sufficiently absorbing hazardous light and IR light in the solar light in a coating film thickness, when spray- coated in a stock solution concentration determined as a spraying standard liquid, a surfactant and a stabilizer into a transparent and weather-resistant synthetic resin emulsion. The stock solution can be diluted with water in an amount of up to about 50%, and is spayed and coated in the optimal concentration determined to give a desired coating film, namely a desired light-cutting effect.
