As it is known, the Turbine Inlet Temperature (TIT) in Gas Turbine systems is a critical parameter influencing both material and coating lifetime of turbines as well as their efficiency. The availability of instrumentation capable of providing on line TIT measurements would allow to control the plant operating conditions in such a way the Gas Turbine efficiency can be maximized (by increasing the gas temperature) without exceeding the limits for materials and coatings operation. Unfortunately, because of the very critical operating conditions (high gas temperatures and pressures) at present there are no available methods to accurately measure this parameter on operating plants. For these reasons we have developed a temperature sensor based on spectroscopic photometric measurements of the infrared radiation emitted in a selected wavelength band by the CO2 molecules of the combustion gases. Aim of the sensor is to measure on line and in real time the average gas temperature on a plant section transversal to the gas flow. The developed sensor prototype is mechanically robust and thermally resistant so to withstand typical operating conditions of industrial gas turbines. It has been tested both at laboratory level in controlled stable conditions and on a full scale combustor test bed simulating the behavior of real gas turbine machine. In both cases, however, the recorded signal, which is in the IR spectral region, could be affected by contributions arising from black body emission of the hot wall located in front of the collecting optics. In this paper we present the results of laboratory tests carried out to evaluate this effect.