Thanks Aquilauno and Chris, very useful and well oriented your opinions and advise. Yes, I have a little led lamp that I used on my PC, it has a usb connection, I tested this unit on the keyboard and it seems works fine, BUT as said by Chirs and Aquilauno is better not to stress and overload the keyboard usb plugs, the damage of one of these usb plugs could be a very painful situation a led lamp with its own power supply, rechargeable etc. I think is the best choice and also very useful in dark situations. Thanks.
Best regards
Bernardo