Hahaha I see myself but 3 years ago from your question … and because this is your first post so I would like to drop by here with you few second before going back to Mars . Let keep moving next guy then you will see what you are looking for … cheers !
In this example https://examples.blynk.cc/?board=ESP8266&shield=ESP8266%20WiFi&example=More%2FSync%2FSyncPhysicalButton
the section that send something to Blynk is this
// Update Button Widget
and this below section from Blynk sends to your board
ledState = param.asInt();
Lastly you could use current sensor like Hall effect sensor to measure whether the light is really ON or OFF … yes you could … let searching Hall sensor …ok I need to go