Hot things glow. Medium hot things (like you) emit lots of infrared light. Really hot things (like lightbulbs) emit infrared and visible light. Ridiculously hot things (like the sun) emit infrared, visible light, and higher-energy radiation (UV etc.).

The exact details depend on the chemical composition of the material, but for a simple model, check out https://en.wikipedia.org/wiki/Black-body_radiation