What does it mean to put out three of the seven longevity lamps?

Seven ever-burning lamps go out, and three have no other meaning. Just rekindle it.

The ever-burning lamp is a form that the ancients used to imply the immortality of life.

There is a double-layer ever-burning lamp, in which the container is filled with lamp oil, the wick is soaked in vinegar, and the outer layer is filled with water to cool the lamp oil; This is a great invention, because the oil consumed by the oil lamp is not ignited, but volatilized by heat. The vinegar bubble wick can not only keep the temperature low, but also the water outside the oil pot can effectively prevent the oil temperature from rising.