Light Flow should do what you want - though I have the paid version. There is a setting that you can enable that automatically switches off notifications while the phone is charging (assuming you charge your phone while sleeping).
Is there a way to disable led notifications?
There is an app called Gmail Notifier which worked excellent until the latest Gmail update and ICS. It is open source and would be great to have someone work the changes to the app. You could set the notification to specific times and days and also change the icon notification in the bar.
I would like to find a quick and easy way to disable the led notification light when I go to bed at night.