Jain Festival Diwali, Jain New Year and Vikrma Samvat :

Diwali is a very important day for the Jains. On this day, Kartika Krishna 14, (dawn of the amavasya) during the swati nakshatra, Lord Mahavira attained Nirvana achieved to a state of absolute bliss. The Lord discarded the body and the bondage of all Karmas on that night, at Pavapuri and attained Mukti or deliverance. 

Diwali is the festival of lights. It is mentioned in Kalpasutra that the King Chetaka of Vaishali with other friend kings, had a great lightning of lights, they thought: "since the light of intelligence (Vardhamana Mahavira) is gone, let us make an illumination of the material matter". There is another view. In the early morning after the day of Diwali, Ganadhar Gautam Swami, the first disciple of Lord Mahavir attained absolute enlightenment. This could be another probable cause for celebrating the Diwali as the festivals of lights. 

Possibly the word "Diwali/Dipavali" first written by Acharya Jinasena in his in "Harivamsha-Purana" on Kartika Krishna 14, (dawn of the amavasya) during the swati nakshatra. It was composed in Shaka Samvat 705. Thus people in Bharata (India) every year celebrate famous "Dipalikaya", to respectfully worship the Jinendra on the occasion of his Nirvana. Diwali is not mentioned in Valmiki's Ramayana, Mahabharata, brahmanical Puranas or in Tulsidas's Ram-charit-manas. So, it is most probably that Diwali is predominantly a Jain custom, which was Indianised later on and is being celebrated by almost every Indian. 

The new Jain year, Vira-Nirvana-Samvat 2529 begins right after this Diwali. This Year Diwali is on 5th November 2002. 
The Vikrama Samvat in Gujarat starts from Diwali. Thus the new (Kartikadi)
Vikrma Samvat 2059 will start in Gujarat. Originally, the Vikrma Samvat 

Synchronized with the Jain year. 

Celebrations and Customs:

This festival is observed in honour of Jain deities and the final liberation of Lord Mahavira, the 24th Teerthankar, from the cycle of life. He died on this day at the age of 72, at Pawapuri in Bihar.

The fourteenth day of the bleak fortnight of Kartik, the full-moon day and the first day of the fortnight of the waxing moon in Kartik - these three days are celebrated with Paushadh, fasting, special repetition of holy hymns, and meditation. Jains observe fast on the on these three days and listen to the Uttaradhyayan Sutra which contains the final message of Lord Mahavir. The whole of the night of Diwali should be spent in the recitation from the holy hymns and in meditation on Shraman Bhagwan Mahavir. In the early morning of the first day of the New Year, Ganadhar Gautam Swami, the first disciple of Lord Mahavir attained absolute enlightenment. The Jains begin the New Year with a glorification of Lord Gautam Swami; and listen with devotion to the nine Stotras holy hymns and with listening to the auspicious Rasa (epical poem) of Gautam Swami from their Guru Maharaj.

On this day, Mahavira is worshipped at midnight and early next morning. Sacred scriptures are recited and houses are grandly illuminated. The festival is celebrated with much zest in Girnar, in Gujarat. Devotees from all parts of the country assemble at Pawapuri and sweets are distributed. The farmers do not raise livestock and try to own bulls for farming.