ELI5: Explain Like I'm 5

Diffuse sky radiation

Diffuse sky radiation is when the sun's light comes down from the sky and spreads out in all directions. It is like when you point a flashlight at a wall and it makes a bright spot on the wall, but when you move the flashlight around and point it in different directions the light spreads out. Diffuse sky radiation is what makes it seem like it's always bright, even on cloudy or dark days.