This is the board for the under stair lighting. The Atmega328 is used to read digital pins connected to photo-transistors that are being illuminated by a laser. In the event that the laser is broken the output of the shift registers will be used to trigger the base of the transistors.
Each transistor has a 10 ohm current limiting resistor. the capacitor / resistor pair that is in parallel with each transistor is used to provide a fading effect. The value of these can be changed to adjust the amount of time it takes for the LED’s to fade out.