It can be explained by different emission spectra of UV source used in experiments. The UV LED which was used has only
one a very strong peak at 365 nm (Fig. 9). The emission line spectrum for mercury lamp has several peaks from 200 to
600 nm, in the UV and visible range as well. The examined materials absorb irradiation in all range and especially in the case
of HDPE, the absorption increase strongly for lower wavelength (UV region). It confirms why HDPE is so much sensitive for
UV irradiation and the chain-scission and recombination reactions occur so intensively