This image is a combination of two images, one taken in visible light and one taken in infrared (IR) light. In the IR thermogram the temperature range goes from hot (white) to cold (blue). Thermography is a technique for visualizing the temperature of surfaces by recording the emission of long-wavelength infrared radiation. This heat radiation is detected electronically and displayed with different colors representing different temperatures. In this image the whiter colors are the hottest. The windows in homes are a major source of heat loss.