  We provide optical reflectivity data collected over a broad spectral range
and as a function of temperature on the ErTe$_3$ and HoTe$_3$ materials, which
undergo two consecutive charge-density-wave (CDW) phase transitions at
$T_{CDW1}$= 265 and 288 K and at $T_{CDW2}$= 157 and 110 K, respectively. We
observe the temperature dependence of both the Drude component, due to the
itinerant charge carriers, and the single-particle peak, ascribed to the
charge-density-wave gap excitation. The CDW gap progressively opens while the
metallic component gets narrow with decreasing temperature. An important
fraction of the whole Fermi surface seems to be affected by the CDW phase
transitions. It turns out that the temperature and the previously investigated
pressure dependence of the most relevant CDW parameters share several common
features and behaviors. Particularly, the order parameter of the CDW state is
in general agreement with the predictions of the BCS theory.
