शङ्कराचार्य विरचितम् एकश्लोकी
किं ज्योतिस्तवभानुमानहनि मे रात्रौ प्रदीपादिकं
स्यादेवं रविदीपदर्शन विधौ किं ज्योतिराख्याहि मे ।
चक्षुस्तस्य निमीलनादिसमये किं धीर्धियो दर्शने
किं तत्राहमतो भवन्परमकं ज्योतिस्तदस्मि प्रभो ॥
Is it your light that shines in the day as the sun and as the bright lamp in the night? Let it be. Which light shines when I close my eyes? (in mental vision) Which light illumines in my mental perception? You are that supreme light that illumines the awareness of 'aham' and I am that light.
(Translated by: Dr. Saroja Ramanujam)
The entire *light* of Upanishads is put there beautifully in that one shloka in such a simple manner. Let me try to elaborate the same with my limited understanding in the following post.
I bow down to that Guru Shankara who is the ever guiding light.
अज्ञानग्रासकं ब्रह्म गुरुरेव न संशयः ||
When there is darkness at night, one can't see anything around, he has to light a lamp to illumine those things. But when the sun rises, the same dark world is now visible owing to sun rays. The commonness in both the sun rays and the lamp's fire is the light by which the objects are illumined. The objects thus illumined are seen by the eye. The same eyes, when closed, still make the objects visible in the antahkaraNa, in our imagination and dreams! Where is the sun then? Where is the lamp then? Where is the world and its objects then? How are those same objects visible with the eyes closed? So the objects are neither seen by the eye nor illumined by the sun/ lamp. That light which illumines is within.
While the mind fades away into deep sleep, what is seen? I see darkness. When the sun sets, the objects are darkened, but still darkness is visible. That darkness, even, is illumined by the inner light. For me to know that I slept blissfully, or to know nothing during deep sleep, I need to exist. That avashtAtrayAtita Self is the one that illumines the darkness of sleep, the waking and dream worlds; the Self illumines the intellect, antahkaraNa, the eyes (senses), the sun and the lamp and thus the objects are perceived!
In other words, if the sun illumined the world, how would I see the world when the sun sets? By the lamp's light? If so, how would I see the darkness without the lamp and the sun? How would I see the world in my dreams without the sun and the lamp to light them? How would I know of deep sleep, or not know it, or see darkness without the sun and the lamp? And to close the loop, how would I see even the sun during the day and lamp during the night if I didn't exist? So I exists as the guiding light. That I, the Self, is the brahman that the shrutI declares as the substratum of everything, that illumines all that is sentient and insentient.
Chandogya 3.13.7 says:
अथ यदतः परो दिवो ज्योतिर्दीप्यते विश्वतः पृष्ठेषु
सर्वतः पृष्ठेष्वनुत्तमेषूत्तमेषु लोकेष्विदं वाव
तद्यदिदमस्मिन्नन्तः पुरुषे ज्योतिः॥३.१३.७॥
There is a light that shines beyond all things on Earth, beyond us all, beyond the heavens, beyond the highest, the very highest heavens. This is the light that shines in our heart.
Katha 5.15 says:
न तत्र सूर्यो भाति न चन्द्रतारकं नेमा विद्युतो भान्ति कुतोऽयमग्निः । तमेव भान्तमनुभाति सर्वं तस्य भासा सर्वमिदं विभाति ॥१५॥
There the sun shines not, nor moon nor stars;
These lightnings shine not, let alone this fire.
All things shine with the shining of this light,
This whole world reflects its radiance.
Kena 1.2 also declares:
श्रोत्रस्य श्रोत्रं मनसो मनो यद् वाचो ह वाचं स उ प्राणस्य प्राणः । चक्षुषश्चक्षुरतिमुच्य धीराः प्रेत्यास्माल्लोकादमृता भवन्ति ॥१.२॥
The Self It is the ear of the ear, the mind of the mind, the speech of speech, the breath of breath, and the eye of the eye...
The world here, the world of the dreams, those heavenly abodes that the कर्मकाण्ड rituals provide for... beyond all those exists a light that illumines all those. That very light is the one in our heart. How else can they be illumined without the existence of I? Who will witness it, who will provide for jIva to be bound to those worlds without being illumined by I? What will the jIva erroneously enjoy or suffer if not illumined by I? How will the jIva even exist without That I? All the worlds that the jIva binds to, gives reality to, thinks of, assumes, errs, enjoys and suffers, including its suns, lamps, and the objects, is but the reflection of the ever-free, ever-shining I, the very Self, the brahman of the shrutI.
ॐ तत् सत्
PS: The mind is in layA in deep sleep, it has not met its end, per se. So, it wakes up to a memory that tells it of darkness in the deep sleep, or of not having any knowledge of time and space, akin to one recalling the samAdhi bliss or sleep bliss in meditation or at other times. That too is *attributed* to the Self, for the mind being illumined in sleep when merged too.
As for the Self being illumining, its not as if it shines on purpose of reflecting in the mind... its self-luminous, thats all. The mind being illumined is a side-effect, so to say, totally unwilling of the Self!