Thus in comparison to Allah, there is no other light, or in other words, He is “the Light of Lights.” That is, He is the light of all lights rather than being the greatest light. Therefore, the belief that Allah is the greatest light, that He is of the sensory lights but the brightest and the most intense – reputedly attributed to the Manicheans – is false.
“Allah is the light of the heavens and the earth.” (24:35)
Without a doubt, by referring to Allah as light, the Qur’an does not intend to identify Him as a physical light. The sensible light is a creature among the creatures of Allah, as is expressly stated in the first verse of Surah al-An’am: “All praise belongs to Allah who created the heavens and the earth and made the darkness and the light.” (6:1)
Muslim philosophers, theologians and Qur’anic exegetes have all provided strong proofs in negating a corporeal aspect for Allah.  Hence, using the word light in reference to Allah does not denote sensory light, which is either a physical substance or a characteristic of matter.
Among the exegete-theologians, Fakhr Razi has probably treated this topic more thoroughly than any other. In his exposition of the Verse of Light, he has formulated six rational arguments why Allah cannot have a body and so consequently the light mentioned in the verse cannot be signifying sensible and material light. (Al-Tafsir al-Kabir). More importantly, there are numerous verses in the Qur’an that negate the coming-into-being (huduth) and corporeality of Allah.
The verse, “There is nothing like Him,” that recurs several times in the Qur’an denies the possibility of any likeness and resemblance of Allah to other existents. Hence, Allah being light cannot be of the nature of the sensible light, for the latter has many instances (while Allah in no way resembles physical phenomena).
In analyzing the meaning of the word light, Allamah Tabatabai explains: “The word light carries a popular meaning, and that is, the thing that lightens dark bodies so that we can see them, and so light is the thing by which all things become apparent and visible. Of course, light itself is essentially manifest and visible; there is nothing else that lightens it. Hence, light can be defined as that which is essentially manifest and makes other things manifest as well. This is the first meaning to which the word light was initially designated. Subsequently, the word was employed, by way of allegory or secondary designation (waz’ thanawi), to indicate whatever made sensible things visible. In a later stage, the word was also applied to super sensible realities. It is in this sense that intellect is defined as a light which reveals the intelligible. All these various usages have stemmed from analyzing the initial meaning of light: “That which is essentially manifest and makes other things manifest as well.” (Al-Mizan)
Thus, what is initially understood by light is the sensible light that emanates from illuminant objects such as the sun, the stars and man-made lamps, without which the world would be shrouded in darkness. Of course, the essence and definition of light from the standpoint of the physicists is a whole different issue. They might consider the reality of light as yet unravelled and they might have disagreements regarding it, but what is for certain is that in the material world there does exist something referred to as light that is radiated from illuminate objects, technically referred to as “sources of light.” The application of the word light, however, is not limited to sensible light. It can be applied to whatever is “manifest and makes manifest” or, put differently, to whatever is “apparent and makes apparent.” For instance, we often refer to knowledge as light, for it is in its essence clear and also sheds light on other realities. (Shaheed Mutahhari, Tafsir Surat al-Nur)
Regarding the believer, the Qur’an states: “He who was lifeless, then We gave him life and provided him with a light by which he walks among the people.” (6:122)
So in the Qur’anic terminology, faith is “light”. And as faith illuminates the heart of the believer, shows him his destination and guides him to felicity, this application of light is correct. This is similar to the gnostics’ reference to love as “light”. Rumi says:
Love is victorious and I, conquered;
As the moon, I am illuminated with the light of Love (Mathnawi)
Using the word light in reference to Allah is correct, for such usage has occurred in the Qur’an and the narrations.  But we must be careful to note that in saying “Allah is light”, we do not intend material and sensible light; rather, that the Divine Essence is manifest and manifestant. The manifestness and clearness of everything is due to the emanation of His Essence. However, nothing illuminates Him. Thus, we can correctly say, Allah is light.
Allamah Tabatabai writes: “Since it is the existence of everything that is the cause of its manifestness to others, the highest form of light is therefore existence itself. Moreover, since the existence of contingent beings depends on the bestowal of existence by the Truth, the Supreme, He is the most complete instance of light. It is He Who is essentially manifest and also makes manifest all other-than-him. All other existents become manifest and existent by virtue of Him. And this is the meaning of the verse, ‘Allah is the light of the heavens and the earth.'” (Al-Mizan)
From the aforesaid explanations the meaning of the Verse of Light becomes clear: Allah is the Creator and the Illuminator of the heavens and the Earth. By the expression “the heavens and the Earth”, what is intended is the entirety of the world of existence – all the celestial and the terrestrial existents; the apparent and the hidden worlds. “The heavens and the earth” does not merely signify the sky above and the Earth that we inhabit. (Tafsir Surat Nur) “Therefore, the meaning of the verse is that Allah is the Light of the entire universe. The reason why the verse has employed this word in lieu of the Creator is to point to the fact that just as light is itself visible and does not need anything else to make it visible, and it is light itself that illuminates all other things, likewise Allah has no creator and there is no other agent that could shed light on Him. He is a manifest, clear and self-evident existence. There is no need for formulating reasoning to prove His existence. He is the Creator of all the other existences of the world of being. In the words of Haji Sabzwari: “O You Who are obscured by the intensity of Your light.” (Manzumah)
Thus, as propounded by the gnostics in following the mystical teachings of the Prophets and the Imams, Allah is manifest to the highest degree; He is absolutely clear, and hence there is no need for the mediation of His creatures to reveal Him. In other words, in order to reason for the existence of Allah, one should utilize the argument of cause rather than the argument of effect. We must first comprehend Allah and then through Him, His creatures, not conversely.
It is to this truth that the following line from the Arafah Supplication (related from Imam Hussain b. Ali) refers: “O Allah! Being distracted by [Your] effects and creatures prevents me from seeing You.”
In Du’a Kumayl, the Commander of the Faithful, Imam Ali b. Abi Talib expresses: “By the light of Your face from which all things are alight.” If not for the light of the Divine Visage and Essence, everything would be dark. That is, nothing would exist, and all things would recede back into the darkness of non-existence.
Without the light of the Divine Essence, the shadow of non-existence would envelope all things; the resulting darkness would not be like that of the night (rather it would be the darkness of non-existence).
Hence, it must be said that Allah is absolute light. In comparison to Him, there is no other light. All other lights in comparison to Him are darkness. For the only existent Who is by His essence manifest and manifesting, is Allah. All other things that are manifest and that illuminate other creatures are by their essences dark. It is Allah Who has bestowed on them that feature.
It is in this light that Allamah Tabatabai has made the following inference from that verse: “Hence it can be inferred that Allah is not obscure, for any existence, for the disclosure of all things to themselves and to other things, derives from Allah’s illuminating. If Allah had not illuminated or brought into existence anything, nothing would have existed. Thus prior to all other things, Allah is the essential manifest being. Hence it can be concluded that light in the verse, ‘Allah is the light of the heavens and the earth,’ refers to that all-embracing Divine light which is the source of the universe, the light to which all things owe their manifestness, the light which is identical with the existence of everything. This is that all-embracing Divine mercy.” (Al-Mizan)
Thus according to the Qur’an, Allah, the Supreme, is not an absent or essentially obscure God that is revealed by His creatures. Such conception is defected and elementary. Real knowledge is to comprehend the world through Allah, not conversely, and this verse asserts that Allah is at the height of conspicuousness, clarity and obviousness.
Another point that can be inferred from this verse is that we refer to Allah as light, not as “the greatest light”, which implies that there are other lights as well, some more bright and others less bright, and that Allah is the greatest. According to the Qur’an, there is only one light and that is Allah, and everything else is dark and non-existent. It is true, however, that in comparing the creatures together, some are light and some are not – for instance, knowledge, faith, intellect etc., are light, but have all derived their light from Allah.
Thus in comparison to Allah, there is no other light, or in other words, He is “the Light of Lights.”  That is, He is the light of all lights rather than being the greatest light. Therefore, the belief that Allah is the greatest light, that He is of the sensory lights but the brightest and the most intense – reputedly attributed to the Manicheans – is false.
In the end, we find it suitable to relate Imam Ali ibnMusa al-Ridha’s (peace be upon him) reply to Abbas ibn Hilal who had asked the Imam regarding the meaning of the Verse of Light: “He is the Guide for the inhabitants of the heaven and the inhabitants of the earth.” (Al-Tawhid)
 These proofs can be found in Kashf al-Murad fi Sharh Tajrid al-I’tiqad pg. 287 and Nihayat al-Hikmah, pg. 275.
 Nur (Light) is one of Allah’s names. Other than the Noble Qur’an, Allah has been addressed by this name in a number of traditions. Some examples are in Kitab al-Tawhid, ch. 29, pg. 194, no. 8 and pg. 195, no. 9 and pg. 219, no. 11 in al-Khisal. In a number of supplications such as Du’a Kumayl and Du’a Jawshan Kabir this name of Allah has been mentioned. It is considered one of Allah’s 99 names. Gnostics have prolonged discussions about these names which we cannot discuss here.
 In Mafatih al-Jinan there is a supplication called “Nur” (light). In it we read: “O Light of Light.”