The plasma medium, created inside the neon indicator lamp, enables the detection of a wide wavelength range of differential or modulated EM signals. The interaction between the plasma and various frequency EM waves are still being investigated and in the mm-wave/terahertz range the interaction mechanism is still not well understood. In this study commercially available neon indicator lamps are studied using both time-domain and continuous wave mm-wave/THz measurement systems. The glow discharge detector response is similar to other commercially available room temperature direct detection mm-wave/THz detectors and performs at a fraction of their cost. Using a W-band Schottky diode multiplied source the detection behavior of the detector was investigated using lock-in detection techniques at modulation frequencies up to 90 kHz. These measurements also show that the orientation of the electrode structure was sensitive to the polarization of the incident field. The polarization sensitive behavior indicates a strong coupling between the incident and native field in the plasma. Furthermore, the interaction of the lamp structure with the mm-wave/THz field was investigated between 260 and 380 GHz using both a home-made time-domain THz spectroscopy system as well as a commercially available mm-wave/THz source. Within the constraints on the maximum modulation frequency of the source (<100 Hz-1 kHz), certain mm-wave/THz frequencies are attenuated suggesting the electrode structure of the detector can play a role in the detection. Overall, the measurements show that certain types of indicator lamps perform better than others and future studies in detection and imaging can benefit from their use.