When used as the detector for a non-contact pyrometer, the thermopile is oriented so all the
concentrated light falls on the hot junctions (the “focal point” where the light focuses to a small
spot), while the cold junctions face away from the focal point to a region of ambient temperature.
Thus, the thermopile acts like a multiplied thermocouple, generating more voltage than a single
thermocouple junction could under the same temperature conditions.