You don't appear to be storing the led array you created inside ApplyButtonPushed to any of the properties of your app, so it's a local variable that gets destroyed (along with the rest of the contents of the function's workspace) when that function finishes executing. You may expect that the VisibleButtonPushed function somehow "finds" that variable from the (deleted) workspace of that ApplyButtonPushed function call but it doesn't. Instead it creates a 1-by-2 struct array each element of which has one field, Color. That struct has no connection to the array of uilamp handles you created in ApplyButtonPushed.
Give your app a property that can store the array of uilamp objects. After creating the led array in ApplyButtonPushed, assign it to that property. In VisibleButtonPushed, get the contents of that property and (after validating that it has been populated by a previous call to ApplyButtonPushed) use it to refer to the selected lamp.
