The emissive power given by a radiation body has some properties:
- The emitted radiation is a continuous function of wavelength. At any specified temperature, it increases with wavelength, reaches a peak, and then decreases with increasing wavelength.
- At any wavelength, the amount of emitted radiation increases with increasing temperature.
- The radiation emitted by the sun, which is considered to be a blackbody at 5780 K (or roughly at 5800 K), reaches its peak in the visible region of the spectrum. Therefore, the sun is in tune with our eyes. On the other hand, surfaces at T ≤ 800 K emit almost entirely in the infrared region and thus are not visible to the eye unless they reflect light coming from other sources.
In bullet point 1 of the slide below, is the same thing as discussed in Radiation.
