@SnapsProvolone hopefully will stop by here, but the above posters are correct.
It's all about amps. You should only put a maximum of 80% load on any circuit. The rest should be 'cold'. This extra space is used for startup etc if necessary.
Running off of a bathroom circuit isn't a good idea ever. To be honest, bathroom circuits should be on their own anyways.
To test for certain, you need at minimum a multi-meter, and properly an "amp clamp" to see what is being drawn through what circuit.
To put things into perspective, a 1000w lamp will use 8.3A on a typical 120v circuit. Give up to 2A for startup. Put in room for fans, (de)humidifiers, etc. Given a 15A circuit with the 80% rule is 12A, math becomes simple.
Reading what's on a label on a panel is always something you need to question. Almost always, somebody's hacked something in that takes away from that.
If you are building a grow room, you want to know for sure what is what, unless you're running something extremely small.
If in doubt, get in a proper electrician, and admit what you want to do. Electrical is funny in the way that if it is calculated or used wrong, it could burn down your house.
-spek