• lightening - the process of changing to a lighter color or the process of adding light or the process of removing weight.
• lightning - a discharge of atmospheric electricity

The local Fox station's morning news program reported that yesterday's shuttle launch was delayed due to "lightening strikes." Fox! They're the best of the bunch, but it seems that even they are not immune to poor editing and proofing. Man, the local stations' news crews are stupid!

Lightning strikes are good at lightening the night sky. Look, I used both words properly in a sentence!