If you have the Windows Backlit Keyboard
On the top right hand side of the keyboard you should have 4 lights. Press the 'On' button to turn on the backlighting and 'off' to turn off the backlighting.
The two extra keys to the right of these control the level of the lights. (there are three light modes.)
If you have the Mac Backlit Keyboard
On the top right hand of your keyboard above the numberpad are two backlight keys. Simply press these to control the light levels.
PLEASE NOTE SLIMLINE KEYBOARDS ARE NOT BACKLIT.
First Generation Hybrid Keyboard. 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.)