You may not have come across the backlit toggle button location on the 'Scroll Lock' key, give it a press to turn the back lighting on/off. Should this not work, please do not hesitate to get in touch and we'll be happy to assist further!

If you have the new Hybrid version of the keyboard you can also turn the brightness up and down by holding 'FN' and pressing 'PG UP' or 'PG DOWN' (you should see the light icon on these keys.)