Adding a IR-controlled light to SmartThings?

Take a look at the z-wave-to-IR extenders made by remotec. The zxt-120 is somewhat popular among community members but it’s meant to control air conditioners and the z-wave side of the device shows up as a thermostat so that’s no good.

However they have other models that I believe are meant to control AV equipment. I know that the extender for a/c’s can learn IR codes from your current remote, so you should check those other models and see if they might meet your needs. The zxt-120 has a working device handler so it can be controlled with ST; I have no idea if any other remotec devices have a device handler developed by the community.

Also, there’s this. If I understand correctly, it can be setup to control individual devices through your harmony. It requires a raspberry pi or other server running on your LAN though, so it may not be super straightforward, depending on your level of tech know-how.