###### Abstract
It is well known that in atmospheric air, the minimum voltage level at which discharges appear decreases with pressure [15; 16], so electric and electronic circuits placed in unpressurized aircraft areas are more susceptible to incidence of electrical discharges [17; 18] compared to sea level conditions [19]. It is known that surface degradation of polymeric samples increases as pressure decreases because discharge activity accelerates at lower pressure [20]. For safety and maintenance reasons, and due to strict regulations, the risk of electrical discharges in airplanes must be minimized. Commercial widebody jetliners have complex harnesses, hundreds of kilometers of wires, and thousands of wiring components, such as connectors, clamps, or terminations. Most of these components are hidden inside conduits, ducts, or troughs [21], so maintenance and failure detection tasks become difficult to apply. Due to their low intensity, electrical discharges go unnoticed by the on-board electrical protections, especially at an early phase. However, their persistent effect degrades insulation materials [22], eventually leading to major failures [23]. Therefore, combined actions, such as an improved design and a plan to monitor the discharges, are required to minimize the severity and occurrence of failures. Monitored data enables application of predictive maintenance actions [18] while increasing aircraft safety and allowing application of remedial strategies before critical faults develop [24]. Wiring systems are critical elements for the occurrence of discharges [7], which are often placed in environments with high levels of acoustic and electromagnetic noise, where conventional acoustic or electromagnetic systems to detect partial discharges would fail. It is in these applications where optical sensors are attractive due to their high immunity to electromagnetic and acoustic noise. Optical sensors detect the light produced during the discharge process [25] due to the different transitions of excitation, ionization, and recombination of electrons induced by the discharge [26]. In the case of using optical image sensors, it is also possible to locate and quantify the severity of the discharges, as proposed in this paper, since it is essential for the reliable, safe, and stable operation of aircraft power systems [27]. This approach makes it possible to study the temporal evolution of discharges,thus opening the possibility of developing state of health (SoH) and remaining useful life (RUL) methods, which are the basis for applying predictive maintenance plans. This field requires more research and experimental data because there is very little experimental work using image sensors for SoH and RUL applications in insulation systems. By analyzing the temporal evolution of the discharges, SoH and RUL tools could provide key information so that remedial actions can be taken before major failures are triggered. Image sensors are increasingly used to detect corona discharges. In [28], the damage caused by corona discharges to polymeric insulating samples was located and analyzed by means of digital photographs, while in [29; 30], the damage caused by mist and acidic fog to polymeric samples exposed to corona discharges was evaluated by means of digital images. In [31], it was revealed that the intensity of the discharges is correlated with the number of photons generated. Using a different approach, in [27], it was shown that under direct current (dc) supply, the electric power dissipated by the PDs is related to the energy of the digital images of the discharges. In [32], the luminosity content of digital images of alternating current (ac) corona discharges was studied and correlated with the measured electric power due to discharge activity. However, [32] lacks a precise analysis, which is required due to the complexity of the electric signals of the discharges, especially due to their low intensity, short duration, and high-frequency content.