Use this recipe to track when lights are turned off in conjunction with another recipe about when lights are turned on: https://ifttt.com/recipes/286799
Then
Add row to spreadsheet
This action will add a single row to the bottom of the first worksheet of a spreadsheet you specify. Note: a new spreadsheet is created after 2000 rows.
ID sKBhXZzE
Explore more great ways to automate Google Sheets and WeMo Lighting