'we cannot know that we are illuminated by a great light'

That light cannot be known directly is expressed in contemporary terms by Peter Russell. When speaking of the light of consciousness, he asserts:
Although all we ever see is light, paradoxically, we never know light directly. The light that strikes the eye is known only through the energy it releases. This energy is translated into a visual imagery in the mind, and that image seems to be composed of light—but that light is a quality of mind. We never know the light itself. 
Russell is speaking from a scientific viewpoint, but the fact that we can never know light itself is helpful in appreciating the working of boundless compassion. When the light of compassion illuminates our existence, it reveals our self-delusions. Hiroyuki Itsuki ... describes this as follows: 
We cannot know that we are illuminated by a great light simply by looking up into the sky. But if we lower our heads and look down at our feet we can clearly see the long, dark shadow that stretches out from us. We know that the darker and blacker that shadow is, the brighter the light that shines upon us.

Taitetsu Unno, Shin Buddhism: Bits of Rubble Turn into Gold.