It’s been hacked, the light bulb is likely part of some botnet or under an attacker’s control directly. Which is why it’s sending that much data continuously. IoT/smart devices don’t send a lot of data in this sort of volume as most of the time they’re idle and maybe send a heartbeat or status update every once in a while to prove they’re alive.

This is what is called an indicator of compromise or IoC, it’s some behavior or pattern that can be used to determine what is happening or who is the one doing the attacking.

Likely OP would need to do some analysis to be able to get attribution unless it’s a very well known botnet actor in which case attribution is fairly straightforward.