Blackbody radiation
It could only give off infrared light and could not give off even ordinary red light, much less any higher energy light such as ultraviolet light or x-ray radiation. Planck said that the total energy given off by a blackbody at any particular frequency is equal to the number of the "vibrating things" (see above), n, that was vibrating at a given frequency, f times a special constant, h, that turns frequency units into energy units. The equation is: