Less than half of the sun’s energy is visible. Longer wavelengths beyond the red part of the visible spectrum are infrared, which is felt as heat. Shorter wavelengths, beyond purple, are ultraviolet (UV).
When the sun’s energy strikes a window, visible light, heat, and UV rays are reflected, absorbed, or transmitted into the house. Low-e glass contains transparent metallic oxides that reflect up to 90 percent of the harmful UV rays.