A definition of Enlightenment by Roberto Assagioli in Transpersonal Development:
“One of the most frequent manifestations of the superconscious in the conscious mind is that of enlightenment, which results from the opening of the ‘inner eye’.
There are many similarities between intuition and enlightenment, but there are also significant differences.
In general terms we can say that intuition is a flash of illumination on a particular aspect or manifestation of Reality. Enlightenment, on the other hand, is broader and longer-lasting. It is a vision that shows the essential nature and synthetic unity of all Reality, or of significant aspects of that Reality. It is the perception of a light that is different from its physical counterpart, a light emanating straight from Reality itself.
This type of enlightenment may be regarded as a revelation of the divine immanence, and as a revelation of the unity of Universal Life expressed in myriad forms. The most effective description is the one contained in the Bhagavad Gita, which refers to it as the ‘revelation of the Universal Form’.
Many poets have experienced this enlightenment and have attempted to express it. The greatest among them is Dante. His ‘Paradise’ is full of expressions of light. At the beginning of the book he states quite clearly that he has had the indescribable experience of the supreme light, the light that shines in the highest heaven, closest to the Supreme Reality, God.
The glory of him who moves everything Penetrates the universe and shines In one part more and, in another, less. 
This manifestation of light takes on various aspects in the conscious mind of the person to whom it is revealed. These aspects are not separate but interpenetrate and merge with one another to varying degrees, some aspects prevailing over the others, depending on individual differences between those who perceive it. Sometimes the dominant factor is beauty, as with Rabindranath Tagore; in other cases it is the cognitive aspect that occupies the conscious mind, e.g. Plotinus and Meister Eckhart.
For Christian mystics, as well as for Eastern ones, this phenomenon involves feelings of love and reverence. For others the main emotion aroused by enlightenment is one of joy reaching the point of ecstatic bliss. I would nevertheless repeat that we are dealing with a situation in which one aspect is being stressed above others: in general they are all present to some degree. Dante gave fine expression to the way in which they blend together.”
 have been in the heaven which takes most of his light,
And I have seen things which cannot be told,
Possibly, by anyone who comes down from up there-,
Because, approaching the object of its desires,
Our intellect is so deeply absorbed That memory cannot follow it all the way.
Translation CH. Sisson, Pan Classics
The sixth group of symbols is that of light or enlightenment. As with the ordinary waking process, in a spiritual awakening one comes out of the darkness of night into the sunlight which is why the awakening of the spiritual consciousness has been called ‘enlightenment’, i.e. the passage from the shadows of illusion to the light of Reality. The first step, corresponding to the first step in the awakening process, is a straightforward (though not necessarily easy) view of ourselves as we really are. The second step, or another effect of enlightenment, is that it becomes possible to solve seemingly insoluble problems by means of the special instrument of spiritual vision known as intuition. (The etymological definition of intuition, as we said earlier, is ‘to see into’, in depth, or to see the reality of things.) Thus intuitive knowledge replaces the knowledge of the senses, intellect, logic and reason. Intuition complements and transcends the knowledge of the senses. It actually brings about complete identification with what one is seeing or contemplating, and enables one to perceive the intrinsic unity between subject and object.
But spiritual enlightenment is more than this. It is like a ‘flash of lightning’, the perception of immanent Light in the human soul and in the world of creation. There are many testimonies to this – that of St Paul on the road to Damascus, for instance – while in Buddhism, particularly Zen Buddhism, one aims, through special discipline, at producing this sudden enlightenment or revelation of the transcendent reality.
Dante’s ‘Paradise’ might be called the poem of Light. The famous verse:
Intellectual light, full of love;
Love of the true good, full of happiness;
Happiness which transcends any sweetness.
Translation: C.H. Sisson, Pan Classics
This is a wonderful expression of the intimate relationship between light, love and intelligence (from intelligere meaning ‘to understand spiritually’).
 Translator’s note: the last line actually seems to have been mistranslated. The original is ‘Happiness which transcends any pain’.