Stairway illumination is required by the IRC code R314.7. One method for meeting this requirement is to install low-voltage stair riser lights. You can either purchase these units preassembled in a number of designs or build your own.
1) Determine the locations of your step lights. Make sure the stair stringers will not interfere with the step light locations. Cut or drill an opening on the riser board to place the recessed step lights. Step lights come in a variety of sizes and shapes. Make sure you follow the manufacturer's instructions for cutting the correct size opening. Place the transformer next to the electrical outlet.
2) Run low-voltage wire from light to light, starting with the light farthest from the transformer. Leave a 6" loop of wire at each step light location.
3) At each light, cut the wire and separate the wires into 2-3" strands. Use a wire stripper to remove about 1/2" of sheathing from each wire and the wires from the light fixture.
5) Match the polarity of the wires. One wire will have a smooth black wire and the other will have white lettering and ribbing. Hold the wire ends together and connect them by twisting waterproof wire nuts to create a tight connection. Wrap the connection with electrical tape.
6) Read the instructions for your transformer. Make sure the on/off switch is turned off. Secure the transformer using mounting brackets to its desired location and run the wires into place and connect. Make sure the photo eye sensor is accessible to sunlight.
7) Plug the transformer into the outlet and turn it on. Test the lighting and set the timer as needed.
8) Unplug the transformer and secure the top cap to hide the low-voltage wire. Be careful not to screw into the wire.