This light bulb's brightness is proportional to the input voltage.
This device can turn ON and OFF with an input music source. We all know that if you connect a light bulb to a music source this light bulb will blink with music. You can connect the light bulb indicator via audio or DC amplifier so that the device can detect low-voltage signals. You can also connect light bulbs to audio filters so that the different light bulbs can turn ON with different frequencies. You can also use comparators to create light bulb bar graph displays.
This is the simplest light bulb indicator that only includes light bulb protection created with four diodes so that the voltage across the light bulb does not exceed 1.5 V. This indicator does not need a power supply. However, you will need a powerful audio amplifier to drive this indicator. The maximum input voltage is plus or minus 11.5 V.