jyotiṣām api taj jyotis
tamasaḥ param ucyate
jñānaḿ jñeyaḿ jñāna-gamyaḿ
hṛdi sarvasya viṣṭhitam

Translation of Bhagavad Gita 13.18

He is the source of light in all luminous objects. He is beyond the darkness of matter and is unmanifested. He is knowledge, He is the object of knowledge, and He is the goal of knowledge. He is situated in everyone’s heart.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

The Supersoul, the Supreme Personality of Godhead, is the source of light in all luminous objects like the sun, moon and stars. In the Vedic literature we find that in the spiritual kingdom there is no need of sun or moon, because the effulgence of the Supreme Lord is there. In the material world that brahmajyoti, the Lord’s spiritual effulgence, is covered by the mahat-tattva, the material elements; therefore in this material world we require the assistance of sun, moon, electricity, etc., for light. But in the spiritual world there is no need of such things. It is clearly stated in the Vedic literature that because of His luminous effulgence, everything is illuminated. It is clear, therefore, that His situation is not in the material world.

He is situated in the spiritual world, which is far, far away in the spiritual sky. That is also confirmed in the Vedic literature. Aditya-varnam tamasah parastat (Shvetasvatara Upanishad 3.8). He is just like the sun, eternally luminous, but He is far, far beyond the darkness of this material world.

His knowledge is transcendental. The Vedic literature confirms that Brahman is concentrated transcendental knowledge. To one who is anxious to be transferred to that spiritual world, knowledge is given by the Supreme Lord, who is situated in everyone’s heart. One Vedic mantra (Shvetasvatara Upanishad 6.18) says, tam ha devam atma-buddhi-prakasam mumuksur vai saranam aham prapadye. One must surrender unto the Supreme Personality of Godhead if he at all wants liberation. As far as the goal of ultimate knowledge is concerned, it is also confirmed in Vedic literature: tam eva viditvati mrityum eti. “Only by knowing Him can one surpass the boundary of birth and death.” (Shvetasvatara Upanishad 3.8)

He is situated in everyone’s heart as the supreme controller. The Supreme has legs and hands distributed everywhere, and this cannot be said of the individual soul. Therefore that there are two knowers of the field of activity—the individual soul and the Supersoul—must be admitted. One’s hands and legs are distributed locally, but Krishna’s hands and legs are distributed everywhere. This is confirmed in the Shvetasvatara Upanishad (3.17): sarvasya prabhum isanam sarvasya saranam brihat. That Supreme Personality of Godhead, Supersoul, is the prabhu, or master, of all living entities; therefore He is the ultimate shelter of all living entities. So there is no denying the fact that the Supreme Supersoul and the individual soul are always different.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

Of the sun, moon and other light bodies, he is the illuminator (tad jyotih), by which the sun shines, by whose power light radiates. The sruti says:

yena suryah tapati tejasendhah

By whose power the sun burns. Taittiriya Brahmana,5

na tatra suryo bhati na candra-tarakam
nema vidyuto bhanti kuto’yam agnih
tad eva bhantam anubhati sarvam

There, the sun does not shine, nor do the moon or stars. There, lightning does not flash, what to speak of fire. Everything shines following he who shines. Katha Upanisad 2.5.15

aditya varnam tamasah parastat

He is like the sun, beyond ignorance Svetasvatara Upanisad 3.8

Jnanam means that which is revealed by the function of intelligence. The Lord is that jnanam. He is what is to be known which, in matured state, must have form and other qualities (jneyam). He is attained by means of knowledge (pridelessness etc.) mentioned previously (jnana gamyam). Being the form of paramatma, he is situated as the regulator in the hearts of all living entities (visthitam).

Commentary by Sri Ramanuja of Sri Sampradaya:

13.18 This (self) alone is the ‘light’ which illuminates things like the sun, a lamp, a gem etc. It is knowledge alone in the form of the effulgence of the self which illuminates a lamp, the sun etc. But a lamp etc., dispel the darkness that intervenes between the sense of sight and its subject. Their illuminating power is limited to this extent. This is said to be beyond Tamas (darkness). The term Tamas denotes Prakrti in its subtle state. The meaning is that the self transcends Prakrti. Therefore, It is to be comprehended as knowledge, i.e., to be understood as of the form of knowledge. It is attainable by means of knowledge — such as modesty etc., already described. It is present in the heart of all, i.e., It is specially settled, or present in the heart of all beings like men etc.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

The Supreme Lord Krishna known as Parabrahma the source of the brahman or spiritual substratum pervading all existence, is the light of all lights, the illuminator of even the sun and the stars. He is shining, resplendently effulgent all things shine from Him, by His light all creation is full of light. Therefore Parabrahma is intouched by darkness and beyond all nescience untouched by ignorance. The Svetasvatara Upanisad III.VII. beginning veda hametam purusam meaning: The Supreme Lord shines more brilliantly then the sun and by realising Him only one attains moksa or liberation there is no other way to accomplish this. It is this knowledge that is to manifest in the functions of the intellect regarding the 20 superlative virtues given in verses 8 to 12. It is also knowable in the form of sound by OM the primordial sound frequency of the Supreme Lord. It is also accessible through spiritual practices and easily attainable by bhakti or exclusive loving devotion to the Supreme Lord. The discovery of the atma or immortal soul within the etheric heart is being emphasised by acquiring knowledge and performing appropriately for self- realisation.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

Since the Supreme Lord Krishna is achieved by experiencing spiritual knowledge, He is understood to be the goal of all knowledge. Know the atma or immortal soul by experiencing the atma. As the Supreme Lord is the bestower of the atma and the atma is only knowable through Him then He is the most worthy object of knowledge. If the Supreme Lord is knowable by other means then the words He spoke earlier in verse 13 jneyam yat tat meaning all that which is worth knowing would make this verse repetitive. Now He affirms here the means to achieve what He revealed as the goal in verse 13 negating any contradiction. The Supreme Lord knows Himself by His Self alone. His knowing is not dependent on any external source outside of Himself. In special cases He is able to be known by others as it is possible to know Him by His desire and also by realization of the atma. But only by His grace can this manifest and without His grace knowledge of Him can never manifest. The Supreme Lord is self illuminated, He is self contented and He is equal towards all. Therefore as He is the foremost of all, He is the object of attainment for all and all jivas or embodied beings should seek His grace for only by His grace can He be known.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

The Supreme Lord Krishna known as Parabrahma is the source of the brahman or spiritual substratum pervading all existence. It is solely His effulgence that illuminates all luminaries such as the sun, the stars, lightning, jewels, etc. with light. These luminaries only dispel the darkness hindering the vision between the eyes and their objects whereas the knowledge of a mere spark of the Supreme Lord being the atma or immortal soul illuminates all physical lights and without the atma knowledge of illumination is not possible. That is why the atma is said to be totally beyond the darkness of maya which is the deluding, external, illusory potency of the Supreme Lord. The illusory nature of maya is ever changing by nature whereas the atma is eternal and unchanging. The atma is itself knowledge as well as the goal of all knowledge and is most worthy of attaining by the acquisition of knowledge. The qualifications to obtain this knowledge is found in the 20 excellent virtues expounded earlier in verse 8 to 12 beginning with reverence, humility etc. which are in the hearts of all human beings albeit dormant or active. The words hrdi sarvasya dhisthitam emphasises that the Supreme Lord Krishna is specially situated in the etheric heart of all living entities.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

13.18 Tat, that Knowable; is the jyotih, Light; api, even; jyotisam, of the lights-of the sun etc. For the lights like the sun etc. shine because they are enkindled by the light of consciousness of the Self, as is known from Upanisadic texts like, ‘Illumined by whose light the sun shines’ (Tai. Br., ‘By Its light all this shines variously’ (Sv. 6.14), and from the Smrti also, as here (in the Gita) itself: ‘That light in the sun…’ (15.12), etc. It is ucyate, spoken of as; param, beyond, untouched by; tamasah, darkness; ignorance. For cheering up anyone who may become disheartened by thinking that Knowledge etc. is difficult to attain, the Lord says: It is jnanam, Knowledge-humility etc. (verse 7, etc.); jneyam, the Knowable, which has been spoken of in, ‘I shall speak of that which is to be known’ (12); and jnana-gamyam, the Known. The Knowable itself is referred to as jnanagamyam, when after being known, It becomes the result of Knowledge. But when It is an object to be known, It is called jneyam. All these three which are such, visthitam, specially exist; hrdi, in the hearts, in the intellects; sarvasya, of all, of all creatures. For these three are, indeed, perceived there. This verse is begun for concluding the topic under discussion:

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

13.13-18 Jneyam etc. upto visthitam. Beginningless is the Supreme Brahman : by means of the attributes (descriptions) like these, [the Bhagavat] describes the Brahman as being not separate from the Supreme Consciousness (or action) expressed in every utterance and [thus] gracing [the seeker] to infer his [or Its] own nature. These attributes however have already been explained. Hence what is the use of a fruitless repetition ?

Sanskrit Shloka Without Transliteration Marks:

jyotisam api taj jyotis
tamasah param ucyate
jñanam jñeyam jñana-gamyam
hrdi sarvasya visthitam

Sanskrit to English Word for Word Meanings:

jyotiṣām — in all luminous objects; api — also; tat — that; jyotiḥ — the source of light; tamasaḥ — the darkness; param — beyond; ucyate — is said; jñānam — knowledge; jñeyam — to be known; jñāna-gamyam — to be approached by knowledge; hṛdi — in the heart; sarvasya — of everyone; viṣṭhitam — situated.