Unlike the LED and neon types of this device, with the incandescent type you can achieve fairly linear control of a signal level by modulating the current through the incandescent lamp. Includes choice of 3, 6, or a 12 volt grain of wheat lamp for very low current requirements, photoresistor (LDR) cell, and heatshrink tubing. You glue the LDR to the side of the incandescent lamp and then slip the heatshrink over them. You fill the ends of the heat shrink tubing with opaque glue, allow it to harden, and you’re ready to go. The LDR (light dependent resistor) cell and lamp combination has an ON resistance of <1,000 ohms and an OFF resistance of >20 Meg ohms.