The high-frequency signal output by the ballast is transmitted to the coil wound on the annular magnetic core, so that a closed induction magnetic field is formed inside the magnetic core, and the annular electric field is further induced inside the lamp tube to excite the lamp tube to discharge and emit light. That is to say, based on the principle of electromagnetic coupling, the discharge characteristics of non electric polarization can be formed, which makes the generation of induction electrodeless lamp possible.
The 253.7nm spectral line radiation of Hg atom is excited based on the plasma discharge formed by the coupling of annular induced electric field, and then the visible light is excited from the phosphor.