@mielprovoost , your topic has been moved to a more suitable location on the forum. Installation and Troubleshooting is not for problems with (nor for advise on) your project 
See About the Installation & Troubleshooting category.
No experience with app inventor and minimal with esp. One way that I can see is to e.g. let the NodeMCU send a message on a regular basis over the connections with the status of the lamp. Or let the Android app query the NodeMCU on a regular basis to get the status of the lamp.
It will probably help others to help you if you can provide the codes (don't forget code tags for the NodeMCU code; use the circled button in below image).
