With photons decoupled from matter, the energy density of the Universe entered the matter-dominated era, and light, which could now travel freely can still be seen in the Universe as the cosmic microwave background (CMB).
The energy density of the Universe entered the matter-dominated era. This was with photons. These photons were decoupled from matter. Light can still be seen in the Universe as the cosmic microwave background (CMB). This was with photons. These photons were decoupled from matter. Light could now travel freely.