It looks like this feature is mostly compatible with Samsung apps. For example, try the Samsung messaging app, and you'll see it works fine. Other apps are hit or miss. If I set the Edge Lighting to "Always", there are a few apps that will work only when the screen is on, such as facebook. But a lot of them aren't working when the screen is off. I use Google's messaging app, and it only will display for me when the screen is on.