“Consider these eight types. What would you say is the necessary condition for the presence of the understanding nature that is the essence of your visual awareness?
If the presence of light is a necessary condition for your visual awareness, then when light is absent so that it is completely dark, you would not be able to see the darkness which in fact you do see. 20 Your mind makes distinctions about light and darkness and the other phenomena, but the essence of your visual awareness does not make these distinctions.
Clearly then, the mind that experiences these conditioned phenomena is not what is fundamentally you. But what is not these conditioned phenomena must be what is fundamentally you. If it is not you, what else could it be?
Master Hsuan Hua’s commentary:
Distinctions are being made when you perceive light and darkness, but not by your visual awareness; rather, they are made by your distinction-making mind that responds to circumstances. Don’t take that to be the essential nature of your awareness. Your knowledge of light and dark is an activity of your mind. Your visual awareness sees everything impartially without making any distinction. The act of seeing is simply to see…. The distinctions you make are made by your distinction-making mind. This particular section of text explains these teachings extremely well in a few words. All transitory characteristics are dependent on something else. They are not part of you. What stays with you and does not go anywhere else, what is not dependent on anyone or anything else — if that is not you, who is it?… It is something you cannot give away. (II, 75)
A New Translation Buddhist Text Translation Society. The Śūraṅgama Sūtra With Excerpts from the Commentary by the Venerable Master Hsüan Hua (Kindle Locations 1575-1586).
It’s commonly taught in science that you only see because there’s light – I grew up with learning that.
But here, the Buddha is saying that if you need light to see, then you wouldn’t be able to see when there’s darkness. BUT you actually “see” the darkness too because you are aware of the blackness. So you see light AND you see darkness. You see when there is light but your seeing does not lapse for an instant when the lights turn out because you still see darkness.
The seeing just sees – but it’s your discriminating mind that makes the distinctions of light and dark (as well as the duality of other phenomena that you perceive). The essence of your seeing just sees without making these distinctions.
So the seeing does not come and go whether there is light or dark – the seeing stays, irrespectively. It’s the light and dark that comes and goes. Light and dark are dependent upon conditions, but the seeing sees irrespective of the conditions of light or dark. What depends on conditions is not you (because they come and go), but what stays with you, irrespective of the conditions is none other than you!
Essence of Buddhism 