First, go in the Philips Hue app to Settings > Light setup > tap on "+" and select manual search and follow the onscreen instructions. The serial number can be found on the lamp base. If this doesn't work, please download the program: hue lamp finder.
This program can be found on the meethue web site (go to Support > and search "lampfinder". Tap on the related FAQ and follow the onscreen instructions.
The "Lamp finder" is available for Windows and MAC/Linus (don't forget to install java jar).
Download the program, run it and follow the on screen instructions. Note: This program will work for all hue products.