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Although Planck data supports the standard \Lambda CDM model, it still allowsfor the presence of Dark Radiation corresponding up to about half an extrastandard neutrino species. We propose a scenario for obtaining a fractional"effective neutrino species" from a thermally produced particle which decaysinto a much lighter stable relic plus standard fermions. At lifetimes muchlonger than 1 sec, both the relic particles and the non-thermal neutrinocomponent contribute to Dark Radiation. By increasing the stable-to-unstableparticle mass ratio, the relic particle no longer acts as Dark Radiation butinstead becomes a candidate for Warm Dark Matter with mass O(1keV - 100GeV). Inboth cases it is possible to address the lithium problem.

Dark Radiation or Warm Dark Matter from long lived particle decays in the light of Planck