Allah is the light of the heavens and the earth

" Allah is the light of the heavens and the earth: His light (in the universe) may be likened (to the light of) a lamp in a niche: the lamp is in a glass shade: the glass shade is like a glittering star and lamp is lit with the olive oil of a blessed tree which is neither eastern nor western: its oil is (so fine) as if it were going to shine forth by itself though no fire touched it (as though all the means of increasing) light upon light (were provided ); Allah guides to His light whomever He wills. He cites parables to make the Message clear to the people; He has perfect knowledge of everything. " 

The physical light is but a reflection of the true Light in the world of Reality, and that true Light is Allah. We can only think of Allah in terms of our phenomenal experience, and in the phenomenal world, light is the purest thing we know.
The first three points in the Parable center around the symbols of the Niche, the Lamp, and the Glass.
The niche is an opening in a wall which is not a window, fairly high from the ground, in which a light (before the days of electricity) was usually placed. Its height enabled it to diffuse the light in the room and minimized the shadows.
So with the spiritual Light: it is placed high above worldly things: it has a niche or habitation of its own, in Revelation and other Signs of Allah; its access to men is by a special Way, open to all, yet closed to those who refuse its rays. The Lamp is the core of the spiritual Truth, which is the real illumination; the Niche is nothing without it.
The Glass is the transparent medium through which the Light passes. It protects the light from moths and other forms of low life (lower motives in man) and from gusts of wind (passions) ...
The glass by itself does not shine. But when the light comes into it, it shines like a brilliant star. So men of God, who preach Allah’s Truth, are themselves illuminated by Allah’s Light and become like illuminating media through which that Light spreads and permeates human life.
The mystic Olive is not localized. It is neither of the East nor the West. It is universal, for such is Allah’s Light.

اللَّهُ نُورُ السَّمَاوَاتِ وَالْأَرْضِ ۚ مَثَلُ نُورِهِ كَمِشْكَاةٍ فِيهَا مِصْبَاحٌ ۖ الْمِصْبَاحُ فِي زُجَاجَةٍ ۖ الزُّجَاجَةُ كَأَنَّهَا" كَوْكَبٌ دُرِّيٌّ يُوقَدُ مِن شَجَرَةٍ مُّبَارَكَةٍ زَيْتُونَةٍ لَّا شَرْقِيَّةٍ وَلَا غَرْبِيَّةٍ يَكَادُ زَيْتُهَا يُضِيءُ وَلَوْ لَمْ تَمْسَسْهُ نَارٌ ۚ نُّورٌ عَلَىٰ نُورٍ ۗ يَهْدِي اللَّهُ لِنُورِهِ مَن يَشَاءُ ۚ وَيَضْرِبُ اللَّهُ الْأَمْثَالَ لِلنَّاسِ ۗ وَاللَّهُ بِكُلِّ شَيْءٍ عَلِيمٌ "