In the Tune of Brahma, Shakyamuni Buddha mentioned the 10 benefits of offering lights:
One becomes like the light of the worldShakyamuni Buddha
One achieves clairvoyance of the pure eye as a human
One achieves the Deva’s eye
One receives the wisdom to discriminate virtue from non-virtue
One is able to eliminate the concept of inherent existence
One receives the illumination of wisdom
One is reborn as a human or deva
One receives great enjoyment wealth
One quickly becomes liberated
One quickly attains enlightenment
The offering of light is a means of dispelling the darkness of our own ignorance, giving rise to clarity and wisdom. We offer them with the wish that their light will illuminate the lower realms and the bardo, assuaging the torment of beings who suffer in darkness. We also aspire that all beings will develop greater mental clarity in order to discover the causes of long-lasting happiness in virtuous actions of body, speech and mind. Finally, we offer them so that the inner light of great knowing will arise in the minds of all beings and remove the darkness of ignorance and intellectual obscurations.
For the deceased – We make light offerings to ease their passage after death, with the wish that they make a positive future connection with a true spiritual path.
For someone undergoing suffering – we offer butterlamps and dedicate the merit who are suffering, with the wish that suffering and its cause may be dispelled.
As a prayer for someone’s long life – You can offer butterlamps on the occasion of someone’s birthday or anytime, with the wish that they remain long in this world to bring benefit to beings.