Reliable measurement of electric current is essential in many technological and industrial contexts, particularly in environments where conventional electrical sensors are limited by electromagnetic interference, electrical contact requirements, or accessibility constraints. Optical sensing strategies based on luminescent materials offer an attractive alternative due to their noninvasive nature, immunity to magnetic fields, and potential for remote operation. In this work, an optical approach for current monitoring is presented using thermally sensitive upconversion luminescence. The sensing system is based on NaYF₄:Yb³⁺,Er³⁺ particles dispersed in a photocurable resin and deposited as a coating on a resistive element. Under near-infrared excitation, the material exhibits temperature-dependent upconversion emissions arising from thermally coupled energy levels of Er³⁺. A calibration procedure was first carried out by correlating the luminescence intensity ratio with temperature over the range 298–328 K. Subsequently, electrical current was applied to a ceramic resistor, and the resulting self-heating was monitored optically through changes in the luminescent response. A clear relationship between the applied current and the luminescence intensity ratio was observed, reflecting the temperature increase induced by Joule heating. The sensor was evaluated for direct currents between 0 and 2.2 A, a range defined by the electrical and thermal characteristics of the resistor. The measurements demonstrated good repeatability and an estimated current resolution of approximately 0.01 A. The calibration was shown to remain stable across different ambient temperatures within the studied range. The proposed luminescence-based strategy enables accurate, remote measurement of electric current without direct electrical contact. Its flexibility, precision, and adaptability to different resistive components make it a promising tool for current sensing in environments where traditional techniques are impractical or invasive.