Sri Aurobindo translates Shwetashwatara Upanishad, Chapter Six, Verse 14: “There the sun cannot shine and the moon hath no splendour; the stars are blind; there our lightnings flash not neither any earthly fire; all that is bright is but the shadow of His brightness and by His shining all this shineth.”
The Rishi reviews the various forms of light in our world and finds that they are all caused by the light of the Supreme, and are essentially pale reflections of the intensity of the Supreme. Just as we know the moon to glow as a pale reflection of the sun’s light, similarly, even the sun is a pale reflection of the radiance of the Supreme.
Light has both a physical and a metaphysical significance. Light signifies knowledge and through the comparison of all the lights of the physical world with the light of the Supreme, the Rishi is also indicating that the Supreme is the source of all knowledge. Whatever light we follow in this world, it is a reflection of the pure, unadulterated and intense knowledge that resides in the Supreme.
Sri Aurobindo developed a Gayatri mantra which captures this sense: “Let us meditate on the most auspicious form of Savitri, on the light of the Supreme which shall illumine us with Truth.” (OM, tat savitur varum rupam jyotihi parasya dhimahi yannaha satyena dipayet.)
There is also an esoteric sense that relates to the spiritual experience of inner light as the higher force enters the mind. Yogis report seeing various types of internal light as their meditation deepens, it can seem like sparks, or lightning flashes, stars, moon or sun. The Isha Upanishad relates that the face of truth is covered by a brilliant golden lid. The Rishis of the Veda and the Upanishads constantly invoke the higher light to bring forth the truth of existence.
Sri Aurobindo, The Upanishads, Shwetashwatara Upanishad, pp.369-384