Why is torch with four cells brighter than one with only two cells?

A torch with four cells is brighter than one with only two cells because it can provide a higher voltage and increased current to the bulb. More cells in a circuit increase the overall power supplied, resulting in a more intense light output. Additionally, the increased energy allows the filament or LED to operate at a higher efficiency, producing more lumens. Essentially, more cells mean more energy available for illumination.