During high power commissioning of the JET LH launcher, the radiation and impurity release has been analyzed from various diagnostics: VUV and visible spectroscopy, bolometry. These two last diagnostics have lines-of-sight viewing the launcher and can provide information about the electron and/or impurity source localisation. Using a database of 800 plasmas, it is concluded that the iron contamination (FeXV and FeXXIII) is very low for 94% of the pulses and increases linearly with LH power. During arcs, a strong and fast increase of the radiation along the line-of-sight viewing the launcher is observed. This diagnostic could provide a tool for arc detection complementary to the RF measurements aiming at reducing the metal contamination in the plasma.