Rated maximum ambient temperature Ta: For luminaire inbuilt control gear, the control gear standard IEC/EN 61347 does not define Ta or its measurement. For independent control gear, the luminaire standard applies.Rated maximum case temperature Tc: Lamp control gear standard IEC/EN 61347 defines the "maximum permissible temperature that can occur on the outer surface (at the indicated place, if marked) under normal conditions and at the rated voltage or the maximum of the rated voltage range".
Importance of Ta and Tc
Electronic components are directly affected by the ambient temperature Ta. If the ambient temperature Ta is too high, the device cannot emit enough heat to the environment. This can result in so-called hotspots (points where the temperature concentrates). The presence of hotspots in the air close to the components may cause premature aging and failure of the devices. The lifetime of an LED driver is based on its ambient temperature. Tc is the highest temperature that may be reached at the Tc point on the drive's surface for safe operation.
Measurement of Ta and Tc
The ambient temperature is very difficult to measure. It is easier and more reliable to measure the Tc temperature. As part of the design process, MOONS conducts measurements for both Ta and Tc, ensuring that both measurements meet the highest standards. And the Tc is shown in the datasheet in the below picture. The luminaire manufacturer can determine the expected lifetime of the control gear based on the Tc temperature, which is easier to measure.