A true blackbody is an idealized concept, but some real materials, like soot, come close to matching it. As an object’s temperature rises, it gives off far more energy. This relationship is described by the Stefan-Boltzmann law, where power is proportional to temperature raised to the fourth power.
So doubling the temperature increases the energy given off sixteen times over. Temperature also changes the color of the glow. Wien’s displacement law explains that hotter objects give off their strongest light at shorter wavelengths.
This is why a metal rod glows dull red when warm, then shifts to orange, yellow, and finally white as it gets hotter. In 1900, physicist Max Planck solved a huge puzzle about blackbody radiation that classical physics could not explain. His solution, that energy comes in small fixed packets called quanta, launched the entire field of quantum mechanics.
Astronomers use this same relationship in reverse. By measuring a star’s peak wavelength of light, they can calculate its surface temperature without ever traveling there. Cooler red dwarf stars glow near 3,000 Kelvin, while hot blue giant stars can top 30,000 Kelvin.
This is also the same physics behind a common incandescent light bulb, which glows because its thin wire filament is heated white hot by electric current.