  The nature of the dark sector of the Universe remains one of the outstanding
problems in modern cosmology, with the search for new observational probes
guiding the development of the next generation of observational facilities.
Clues come from tension between the predictions from {\Lambda}CDM and
observations of gravitationally lensed galaxies. Previous studies showed that
galaxy clusters in the {\Lambda}CDM are not strong enough to reproduce the
observed number of lensed arcs. This work aims to constrain the warm dark
matter cosmologies by means of the lensing efficiency of galaxy clusters drawn
from these alternative models. The lensing characteristics of two samples of
simulated clusters in the warm dark matter ({\Lambda}WDM) and cold dark matter
({\Lambda}CDM) cosmologies have been studied. The results show that even though
the CDM clusters are more centrally concentrated and contain more
substructures, the WDM clusters have slightly higher lensing efficiency than
their CDM counterparts. The key difference is that WDM clusters have more
extended and more massive subhaloes than CDM analogues. These massive
substructures significantly stretch the critical lines and caustics and hence
they boost the lensing efficiency of the host halo. Despite the increase in the
lensing efficiency due to the contribution of massive substructures in the WDM
clusters, this is not enough to resolve the arc statistics problem.
