Plastic scintillators are currently used as the main components of various neutron measurement systems, allowing the obtaining of accurate information on neutron energy spectra and presenting a great interest in nuclear material control, radiation protection, and homeland security fields. The accurate determination of the neutron energy spectrum requires measuring the scintillator response function to mono-energetic neutrons and determining the light output function. In most cases, the response function of plastic scintillators to fast neutrons are dominated with the deposited energy by the recoil protons from elastic collision of neutrons with hydrogen. Therefore, there are two methods to determine the light output function of the protons deposited energy: using mono-energetic neutron beam and mono-energetic proton beam. This work aims to measure and compare two light output functions obtained with both mono-energetic beams. The experimental setup consists of a triple-discriminating (thermal neutrons/fast neutrons/gamma rays) plastic scintillator loaded with lithium-6 and optically coupled to a 2×2 SiPM (Silicon Photomultiplier) array. A Teflon layer covers the scintillator and connects it to the SiPM to reflect the emitted light. The response function to mono-energetic neutrons is measured using the mono-energetic neutron beam of the IRSN AMANDE facility in Cadarache. It is based on using a hydrogen ion accelerator that produces neutron fields at several specific energies over a wide energy range (between 2 keV and 20 MeV). The response matrix obtained comprises six incident neutron energies ranging from 953 keV to 14800 keV, the low energy threshold of the detected neutrons is evaluated around 953 keV. The second response function is measured using Cyrcé cyclotron at IPHC in Strasbourg, which allows producing protons with energies ranging between a few MeV to 25 MeV. The obtained response matrix is formed by six incident proton energies ranging from 5.9 to 19.97 MeV. The measured response function using mono-energetic neutrons have quasi-rectangular shape extending from the light output of the low energy discrimination threshold to the light output of the full incident neutron energy. The pulse height spectrum obtained with mono-energetic protons have Gaussian shape where the mean corresponds to the light output of the incident protons energy. However, protons lose part of their energy in the Teflon layer before interacting with the plastic scintillator, which makes the incident proton energy reduced. In the final contribution, we will calculate, by simulation, the energy lost by the protons in the Teflon layer and then compare the two light output functions obtained with both mono-energetic beams. Based on these results, a unique light output function will be determined.