The Visible Glow of Hot Things
Hot things glow through a process called "blackbody radiation." This graph shows how increasingly hot things glow across the visible and infrared spectrum.
Very hot objects, like our sun, glow brightly and put out most of their light in the visible spectrum. Shifting to cooler temperatures, like a filament in a light bulb, decreases the light and shifts it more towards a warmer orange glow. At increasingly lower temperatures, like the element in an electric heater, the peak output shifts to the red and infrared parts of the spectrum.
Even cold objects emit blackbody radiation, but do so entirely in infrared light.