A light giving/signifying strength, goodness, hope and brightness all around with lot of holy and mythological significance of a simple Diya/Lamp.
A festival of lights Diwali is having many mythological significance and a belief of lighting up oil/ghee lamps/diyas. This festival is connected with mythological incidents.
The stories revolving around Lord Ram and Siya; Krishna and Satyabhama.
A kingdom Aayodhya where a handsome, obedient prince maryada purshotam Ram was born and his brothers Lakshman, Bharat, Shatrugan; the bond and love between them were amazing and later all got married to the princesses of Kingdom Jankpuri where a beautiful, dutiful, caring and lovely princess Siya was born from Bhoomi and her sisters Urmila, Mandavi, Srutkeerthi. After the marriage when they return to Aayodhya, he was asked to leave kingdom and go for the vanwaas and lead a life as Brahmin, obeying his father and step-mother’s order he agreed and all set to leave the palace but was joined by his wife Siya and small brother Lakshman. They lead a simple life but in the last year of his vanwaas, Siya was kidnapped by the king of Lanka; Ravana to avenge his sister’s pain of nose which was cut/ hit by the bow of Lakshman by mistake. Jatayu a bird tried fighting Ravana but lost his life and when Ram came to know he asked help from Bali and where he met his devotee Hanuman; who flied a long way to lank with a message of Lord Ram and ensure Siya ji’s well being. After Ram worship the god of ocean, Varuna they built a stone bridge with help of vanar sena and writing the name of Ram on stone which floated on the water of ocean. They crossed the bridge and rested for a while where they met Vibhishan – brother of Ravan; who helped Ram how to kill Ravan. After the battle when they returned to Aayodhya the kingdom was completely decorated with Banana trees and the oil/ghee lamps/diyas were lit due to which the dark sky was glowing like day. These lighting diyas/lamps were lit with belief and significance of victory of good over evil.
Which is celebrated with full of joy and lightings till the date as the victory of Good over Evil.
There is another mythological story revolving around Lord Krishna and Satyabhama and their victory of killing Narkasur.
A demon Narkasur; powerful and strong who misused his powers and captured yogi, pundits and 1600 women and attacked Indra lok , seized the glittering earrings of devas mother, Aditi and killed deva mercilessly. Indra dev seeks help from Krishna. Hearing this Krishna and his wife Satyabhama was enraged. Stayabhama was the reincarnation of Bhoomi Devi or Mother Earth was the mother of Narkasur and had owed to stop him and his terror as he was blessed that he would only with hands of woman. Krishna and Satyabhama travled and chased Narkasur; a fierce battle took place between Satyabhama and Narkasur after which he was killed but during his last moments he asked for apologized for his what all dark/bad work he has done and asked Krishna and Satyabhama that the day must be celebrated as the victoryof Light over Darkness by lighting diyas and decoerating homes. Krishna granted his wish and returned his palace and got himself cleaned off the blood and celebrated the day as Naraka Chaturdasi the second day of Diwali.
SO the both mythological stories have one significance the win over darkness with strength, will and goodness and Light prevails and the lighting up of diya has a scientific significance too.
According to science the ghee/oil lamp/diya kills the germs in the air around diya and purify the air.
There are also a story/saying that a diya depicts human nature which is grilled in fire to make them human or soulful. The oil in diya depicts the thoughts or impurities of human body and the batti depicts as soul of human and the fire is the problems which grill humans and clean our souls and set it free from all bad thoughts.