Best way to visualize graph: Times when a Device has been turned On

I have an app that monitors anywhere from 1-100 devices

These devices can be turned ON & OFF at anytime

The user needs to see times when the devices have been turned ON only.

I have drafted a graph as follows:

enter image description here

Questions:

  1. Is there a better way to visualize this information? It doesn't necessarily have to be a graph although I think that makes the most sense
  2. Should each device be represented by a different color?
  3. If I have, say, 100 devices, should I still use a graph?
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