Dispute between Brahma and Vishnu
To resolve a dispute between Brahma and Vishnu, Sri Siva created a limitless Pillar of Light and challenged the Gods to find the column's top and bottom. Brahma and Vishnu both failed in their tasks and subsequently prayed to the Lord that the blazing pillar should establish itself as a Hill, and that Sri Siva should take the form of a lingam on the east of the Hill. They also entreated that, as a remembrance of the fiery column, a Jyothi should appear every year on the top of the Hill during the time of Karthigai (i.e. period of Deepam).
         Brahma's and Vishnu's prayers were granted and the blazing pillar of light became a Hill and a lingam soon appeared at its foot on the south-east side. For the purpose of worshipping that lingam, which is no different to the Mountain, the Gods caused a great Temple to be built around it. A sacred tank was dug and filled with a mixture of all other tirthas (sacred watering places) to provide water for the ablution of the Lord as lingam. And nearby, for the abode of those striving for spiritual achievements, a great city Aruna (previous name for Tiruvannamalai) was built.

Parvati's Penance
The 'Skanda Purana' tells of the legend in which the Goddess in order to expiate her sin of slaying the demon Mahisasura, completes her austerities of atonement on the evening when Krittika was in conjunction with the Moon in the month of Karthigai (November-December). The Goddess says to the Lord:
"O Lord of Devas, this refulgence has been shown by you who are endowed with grace. It has been seen by Devas and human beings directly in the month of Karttika at the great festival of the conclusion of my holy observances. Let your great refulgence be seen (on the day) with the constellation named Karttika. By seeing this supreme brilliance every year, let all the creatures be liberated from all sins."

In further propitiation of the Goddess' penance the Lord and the Goddess merge into each other with their bodies uniting into the form of Ardhanarisvara; showing the form of Shiva and Parvati:
"It was as though two objects were simultaneously perceived in close proximity. In one half it was as white as camphor and in the other half it is as red as red lead. The body of a single unit was highly wonderful. In one-half there was flowing tresses. In the middle of the necklace there was a flower. The body of the crescent moon-crested Lord had silk in one-half that was beautiful with a single anklet, ear-ring and bracelet. The body of the companion of Kubera shone with a single breast... "

Siva said:

" . . . This Durga, the destroyer of Mahisa, the deity born of your part, shall be present here itself, yielding the siddhi of mantras to men . . . Here in the sacred place of Aruna I shall also remain by the name of Aruna. You shall also be here by the name of Arunadevi. Since Aruna and the Lord are always present here, all the siddhis will be easily accessible in this holy spot of Aruna to those who entertain a desire for them."
The Deepam festival follows the moon calendar so each year the date is different however it always falls when the star Krittika is in conjunction with the Moon in the month of Karthika (November-December).

Isanya Desikar and the River
Isanya Desikar, whose math is located just outside Tiruvannamalai on the old pradakshina road, was a distinguished yogi who, like many before and after him, felt the spiritual call of Arunachala. He was born in 1750 in a small village called Rayavelur in northern Tamil Nadu. He came and settled at the foot of Arunachala only late in his life, but nevertheless, by virtue of his intense and personal relationship with Arunachaleswarar, he is regarded as one of the major saints of Arunachala.
         Isanya Desikar had a western devotee, who is now recalled by the name of Ayton. He was the then District Collector for the region that extended from Tiruvannamalai to Vriddhachalam. Ayton had heard about the greatness of Isanya Desikar and approached him in the hope of getting a cure for the tuberculosis from which he had been suffering for many years. Isanya Desikar smiled and after a brief pause spat on the ground. The moment he spat, Ayton was cured of the disease. Ayton then spoke to the holy man with both trepidation and devotion.
'Swami, I have recently acquired a large amount of land, I would like to offer your holiness as much as you need. It can be a permanent endowment in your name.'
Isanya Desikar smiled and asked tauntingly, 'Will your land yield crops even during a drought?' Then, pointing his finger towards Arunachaleswara and Apeetakuchamba, he added,
'Here is a householder with two children and a large family. It is proper to give him any amount of land, but it is not proper to gift it to me, a sannyasin.'
Ayton took leave of him but returned on many occasions. He got into the habit of addressing him reverentially and affectionately as 'Tata', which means 'grandfather'. It is said that before he began any new project he would always meditate on Isanya Desikar and invoke his blessing by saying, 'Tata, please lead me in this work. It is your work.' At Deepam Festival Ayton would take the lead in dragging the huge temple chariot through the streets of Tiruvannamalai. However, before moving the chariot for the first time he would pick up one of the ropes and exclaim loudly: 'Tata, you hold the rope and lead us!' The local people were all astounded that such a prominent British official should have such devotion towards a naked sannyasin.
         Ayton made it a point always to attend and lead this annual festival, but one year he found himself stranded by floods on the southern side of the River Pennar just before the beginning of the festival. Knowing that he was expected to be at Arunachala to start the chariot on its journey, he called out to his mount: 'Horse, I must see Tata and I must also get the Deepam Festival started. Think of Tata and cross the river!' Without a moment's delay or hesitation, the horse leapt into the raging torrent of water and effortlessly waded to the other side. None of the other people who were stranded dared to follow for they were all convinced that it would be suicidal to enter the surging waters.
         At the moment when Ayton put his faith in Tata and leapt into the water, Isanya Desikar opened his eyes after a long meditation and stretched out his hand in a southerly direction. When one of his disciples asked what he was doing, he replied, 'If someone falls into a river, should we not save him?'
         Ayton arrived safely and took Isanya Desikar's blessings to start the festival. When the news of Ayton's spectacular river crossing and Isanya Desikar's role in it spread among the Deepam crowds, many of them came to the north-eastern side of the hill to see the man who had been responsible for the miracle. Several of the new visitors turned out to be mature seekers who were looking for guidance from a Guru. Isanya Desikar accepted some as disciples, had a small thatched shed built to accommodate them and gave instruction by writing a guide to liberation entitled Jnana Kattalai.

King Vajresan
Long ago, King Vajresan of Panchala who was childless, was blessed with a son after having darshan of the Arunachala Deepam in the month of Kartika. The son was named Shatrujith. The prince grew up to be lecherous man. He once eloped with the wife of a Vedic scholar and came to Tiruvannamalai and entered the Temple of Arunachaleswarar.
         It was the day of the festival of the beacon. The paramour made a wick out of her sari and lit the lamp with castor oil. At that moment the Vedic scholar came there and in a fit of rage stabbed his wife and the prince. And in turn the prince killed him.
         Since it was a gruesome murder committed in the sacred precincts of the Temple the three were about to be taken to hell by the messengers of Yama, lord of death. At that moment the messengers of Siva intervened and claimed the prince and the woman as their own and took them to the abode of Siva. Their blasphemous acts were condoned by Arunachala Himself because the wife made a wick and the prince helped her to light the lamp for the Supreme Lord.
         But the Vedic scholar was puzzled, as he was held by the messengers of Yama. The prince, moved by the plight of the Vedic scholar, ordered the vessel used for lighting the Karthigai lamp to release the scholar. Immediately the Vedic scholar was liberated. Thus all the three, despite their misdeeds, were taken to the abode of Siva, as the merit gained by the simple act of lighting a lamp on Kartika day in his Temple outweighed their devilish acts.

The Ghee Lamp, Rat and King
While Lord Shiva was seated in Mount Kailas with Devi Uma, a ghee lamp was in the process of extinction. A rat nearby approached it to drink the ghee and in that act the wick was pushed out a little, enabling the flame to brighten. This pious act though unintentional, resulted in the rat securing a human birth with huge wealth and the rank of a King.
         With that prosperous boon the rat was born on earth as Mabali. Mabali, while reigning in all glory, one day wanted to worship Siva and went to a Siva shrine with all his royal paraphernalia. While in the Temple, a drop from a ghee lamp fell upon Mabali. The King got sores from that one drop and his malady continued for a long time.
         It was then Lord Siva proclaimed, "King, thou art very arrogant. Hence you got this trouble through me. From this day on if you light Shiva shrines with ghee, you will be rid of your sores and live happily." Highly delighted on hearing these words the King from that day commenced lighting Shiva Temples and dark places with ghee (clarified butter) lamps. Lord Shiva looking at the king's piety, gave him liberation in the month of Karthigai on star Krittika during poorva paksha.
         It is for the reason the Lord appeared before the King in the form of Light, that Deepam Darshan is celebrated in all Siva Shrines on this same day every year.