Nokia N97 mini allows users to change the notification light using Phone setup settings. By default notification light appears during a missed call and when a new message or email message is received.
If you want to display notification light only for missed call then you can do the following
Click on the menu button.
select Settings from the Menu
Select Phone from the menu list and navigate to Notification lights
In the Notification light screen, select Events notified option
In the Event notified screen, un check New Message and New e-mail option. Click OK to save the changes.
This change to Notification light would display notification light only when a missed call occurs.