The magnitude of the transmittance of solar radiation through glass is dependent upon its angle of incidence, the emissivity of the glass surface and the length that the light beam travels through the glass. To alter the emissivity of a glass surface a solar-control film can be attached to it. However, none of the present generation of 'solar' films that are applied to transparent glass surfaces is able to inhibit insolation gain during the summer while providing satisfactory thermal-radiation insulation with respect to energy leaving the building during the winter. This is because different wavelengths of radiation need to be inhibited for these two processes to be successful, namely short-wave radiation in the case of insolation and long-wave radiation for thermal insulation. Neither of these films inhibits glare satisfactorily. As expected, the energy transmittance and rate of heat gain by the affected room decrease as the angle of incidence (of the energy source, i.e. the sun, with respect to the glass) increases. Also the magnitude of this rate of heat gain depends upon the type (reflective, insulating or absorptive) of solar-control film applied to the glass.