Interesting the regular LED would emit enough IR to function but it makes sense. Also makes me wonder if the IR detector might respond to some visible light too. ...probably a little of both, but more of LED emitting IR.
I have used IR LEDs and detectors, and they can be hard to troubleshoot as you cannot see the IR LED. However most cell phones do not have an IR filter, so you can use the camera on the smartphone to detect if the IR emitter LED is working.
--Thanks for the reply! --3D
RE: Pyrometer - Non Contact Temperature Measurement