What is the blue light for on the Nintendo DSi

The blue light on the DSi is the Power LED. Here are some facts about it straight from the manual:

• Solid blue means you have a full charge.
• Solid red means that your power is low and the DSi should be recharged the next chance you get.
  
• Flashing red means that your power is very low. You should save immediately. (From my personal experience, when the light flashed, my DSi died within about one or two minutes.)
• Blinking blue while the DSi is closed means that the system is in sleep mode,(something that happens every time you close your DSi while it's on), and is conserving battery power.