[en] The second harmonic X-mode electron cyclotron emission (ECE) from high-density plasma (the electron density is more than 50% of the cut-off density) is analyzed taking into account the refractive index and the influence of polarization in low field operated large helical device (LHD) (the magnetic field B₀=1.5 T). The density dependence of ECE is obtained and compared with the predictions of a theoretical model. It is concluded that the density dependence significantly influences the measurement of T_e by ECE in LHD