Bereshit B: Chapter 28
The third chamber: Netzach

This chamber holds Light in its purest form - Light that is unseen and not yet manifest. Sunlight in the vacuum of space is the clearest illustration of this Kabbalistic truth. Because they lack a physical object to reflect and reveal the Light, the photons of sunlight remain imperceptible to the naked eye. This is why darkness surrounds the earth even though the sun's rays are continually streaming. Sunlight only illuminates when it strikes the physical atmosphere.