The circuit is useful for audio/music lights. The circuit drives the 1.5 V light bulb. There is a similar product on Elecrow: https://www.elecrow.com/light-bulb-indicator.html. The problem with that product is that a high current output (power amplifier) is required to drive the light bulb. Our product does not need a high-current power amplifier. You can connect this circuit to the output of an operational amplifier or a digital-to-analogue converter of a microcontroller.