What does it mean to have your App certified as “Lightning Ready?” It means that you as the provider have taken into consideration the various use cases of your app, it’s features, and various visual elements and have committed to ensuring they work as designed in customer orgs where Lightning is enabled.
The 2017 Requirements
Create/Update the App to ensure 100% Lightning coverage
Update your AppExchange listing
Include Lightning screenshots
Log a Case within the Partner Community
Learn more about what it means to be "Lightning Ready" in our Lightning Lesson titled, Are Your Apps... Lightning Ready?