The butter lamp is a lamp burning clarified butter or oil, offered before an image, and the offering of light is one of the most widespread acts of devotion across the traditions of India and the Himalayas.
Light as offering
In Tibetan temples the lamps are offered in rows of dozens or hundreds before the images, their massed flames a standing offering of light, and in Hindu and Jain worship the lamp appears as the diya, waved before the deity in the rite of arati or floated on water and set out in great numbers at the festival of lights. The flame signifies the dispelling of the darkness of ignorance by the light of wisdom, and the offering of it is an act of honour and of merit, so the same simple object carries a common meaning across several traditions.
A shared devotion
That the butter lamp and the oil lamp recur across Tibetan Buddhism, Hinduism and Jainism, with closely related meanings, reflects a shared devotional vocabulary of the Indian religious world, in which the offering of light before the sacred is a basic and ancient act. The lamps are tended and kept burning as a continuous offering in many temples, the replenishing of them a daily labour of devotion, and the sponsoring of lamps is a common way for the laity to make an offering. The object is humble, but the offering of light it performs is among the most universal and most legible acts of worship in these traditions.