I always to make a project that would control my room lights and fan. In winters it is very hard to get out of bed and switch on/off the lights so I thought of making this project.
This projects uses Blynk mobile app to connect to the server and control my lights. I have also used a single channel relay to act like a switch.
In general, the point of a relay is to use a small amount of power in the electromagnet -- coming, say, from a small dashboard switch or a low-power electronic circuit -- to move an armature that is able to switch a much larger amount of power.
The relay is connected to the digital pin 8 of the uno. One of the wire from the bulb is cut in two parts, one part is fed to the NO port of the relay and the other one to the COM port. Please make the connections properly because you can easily short your uno as I did in my first attempt.
After the connections just make a dashboard in Blynk app. Attach the digital pin to the button and a virtual led to check the status. After setting up everything, just power the uno and you are good to go.
Happy Hacking :)