Unlike previous Apple optical mice, you may notice that you can't see the tracking light on the Apple Wireless Mighty Mouse. This is normal.
The Apple Wireless Mighty Mouse uses a improved laser optical tracking system. Because the laser operates in the infrared part of the spectrum, it remains invisible the human eye. It also operates at such a low voltage that it is harmless if directed into the eye.
Click here for more details on the Apple Wireless Mighty Mouse.