• The Calm Photosphere and the Active Chromosphere • The photosphere is the visible "surface" of the Sun. The name means "sphere of light". From this thin layer - which is only about 300 km deep - most of the Sun's energy is emitted in the form of visible and infrared radiation. It is particularly well visible in white light or in the light of the ionized calcium (the spectral K-line). The temperature in the photosphere decreases steadily from about 6400 degrees at the base to about 4400 degrees