The guarding of the intellect may appropriately be called light-producing, lightning-producing, light-giving and fire-bearing, for truly it surpasses endless virtues, bodily and other. Because of this, and because of the glorious light to which it gives birth, one must honour this virtue with worthy epithets...
{Those who have become contemplatives} bathe in a sea of pure and infinite light, touching it ineffably and living and dwelling in it. They have tasted that the Lord is good (cf. Ps. 34:8)...
("Philokalia (Vol. 1)", p 192, text 171)
... The sun rising over the earth creates the daylight; and the venerable and holy name of the Lord Jesus, shining continually in the mind, gives birth to countless intellections radiant as the sun.
("Philokalia (Vol. 1)", p. 197, text 196)
When in fear, trembling and unworthiness we are yet permited to receive the divine, undefiled Mysteries of Christ, our King and Lord, we should then display even greater watchfulness, strictness and guard over our hearts, so that the divine fire, the body of our Lord Jesus Christ, may consume our sins and stains, great and small. For when that fire enters into us, it at once drives the evil spirits from our heart and remits the sins we have previously committed, leaving the intellect free from the turbulence of wicked thoughts. And if after this, standing at the entrance to our heart, we keep strict watch over the intellect, when we are again permitted to receive those Mysteries the divine body will illumine our intellect still more and make it shine like a star.
("Philokalia (Vol. 1)", p. 179, text 101)
Just as he who looks at the sun cannot but fill his eyes with light, so he who always gazes intently into his heart cannot fail to be illumined.
("Philokalia (Vol. 1)", p. 180, text 108)
You should not doubt that the intellect, when it begins to be strongly energized by the divine light, becomes so completely translucent that it sees its own light vividly. This takes place when the power of the soul gains control over the passions. But when St. Paul says that "Satan himself is transformed into an angel of light" (2 Cor. 11:14), he definitely teaches us that everything which appears to the intellect, whether as light or as fire, if it has a shape, is the product of the evil artifice of the enemy. So we should not embark on the ascetic life in the hope of seeing visions clothed with form or shape; for if we do, Satan will find it easy to lead our soul astray. Our one purpose must be to reach the point when we perceive the love of God fully and consciously in our heart ...
("Philokalia (Vol. 1)", p. 265, text 40)
At the start of the spiritual way, the soul usually has the conscious experience of being illumined with its own light through the action of grace. But, as it advances further in its struggle to attain theology, grace works its mysteries within the soul for the most part without its knowedge...
("Philokalia (Vol. 1)", p. 276, text 69)