Only some Indian Buddhists celebrate Diwali. There are good reasons why Indian Buddhists should consider it important more generally.
Those Buddhists celebrating Diwali do so in remembrance of Emperor Ashoka (r. 268-232 BCE). Around the year 260 CE, Ashoka embraced Buddhism and adopted the principles of the Dharma as the basis for his governance of his empire.
The practice of government should not tolerate suffering. Ashoka in his edicts emphasized the importance of humane government and the welfare of his people. His state built infrastructure and provided free medical care to his subjects. He advocated religious tolerance and called for harmony and respect between all sects in the empire.
He is considered by many Buddhists as the ideal cakravartin, the universal sovereign who rules benevolently. Ashoka unified the subcontinent and and his policy of Dharma applied equally to all of his subjects. In preaching virtue and benevolence in government, he can be seen as a political counterpart to the Buddha.
In today’s darkness, the light of Diwali deserves to shine in Ashoka’s example.
 Skr. “wheel turner”