Infrared Vision

Unlike visible light, lack of light is rarely a problem in the infrared; room temperature objects typically are almost as bright in the infrared as they are in full sunlight. The problem, instead, is contrast. Everything glows, so there are no shadows. Hot objects glow more, and objects with a high emissivity glow more, but most organics are fairly close (metals have very low emissivity). The infrared pictures you see are false color images with quite a lot of postprocessing being done; measuring raw intensity, a spot of warm skin (98.6F) against cool skin (90F) looks something like this, and even against a 70F backdrop only looks like this.