Abstract: Optical emission spectroscopy (OES) is a widely used optical technique for diagnosing plasma parameters; however, OES cannot spatially resolve plasma. In order to obtain plasma parameters with high spatial resolution at low cost, local optical emission spectroscopy (LOES) was developed. It can achieve a high spatial resolution by inserting optical fiber into the plasma to collect spectroscopic data emitted from a hole in the front of the optical fiber. The principle of LOES technology is introduced. Argon plasma is excited by mosquito-repellent incense radio frequency (RF) antenna on a linear experimental advanced device (LEAD), and the light intensity of plasma measured by LOES and electron density of plasma measured by Langmuir probe (LP) under different RF power and radial position is compared. The transition of plasma from inductively coupled (ICP) mode to helicon mode was observed at an RF power of about 500 W. The results show that there is a positive correlation between the light intensity measured by LOES and the electron density measured by the Langmuir probe in our laboratory. It proves the reliability of using light intensity to characterize electron density, and is complementary to the existing LP on LEAD in the diagnosis of different plasma modes.