  We report optical spectra of Lu$_5$Ir$_4$Si$_{10}$ and Er$_5$Ir$_4$Si$_{10}$,
exhibiting the phenomenon of coexisting superconductivity or antiferromagnetism
and charge density wave (CDW) order. We measure the maximum value of the charge
density wave gap present on part of the Fermi surface of Lu5Ir4Si10,
corresponding to a ratio 2\Delta/k_B T_CDW \approx 10, well above the value in
the limit of weak electron-phonon coupling. Strong electron-phonon coupling was
confirmed by analyzing the optical conductivity with the Holstein model
describing the electron-phonon interactions, indicating the coupling to phonons
centered at 30 meV, with a coupling constant \lambda \approx 2.6. Finally we
provide evidence that approximately 16 % of the Fermi surface of Lu5Ir4Si10
becomes gapped in the CDW state.
