  Radio networks (RN) are distributed systems (\textit{ad hoc networks})
consisting in $n \ge 2$ radio stations. Assuming the number $n$ unknown, two
distinct models of RN without collision detection (\textit{no-CD}) are
addressed: the model with \textit{weak no-CD} RN and the one with
\textit{strong no-CD} RN. We design and analyze two distributed leader election
protocols, each one running in each of the above two (no-CD RN) models,
respectively. Both randomized protocols are shown to elect a leader within
$\BO(\log{(n)})$ expected time, with no station being awake for more than
$\BO(\log{\log{(n)}})$ time slots (such algorithms are said to be
\textit{energy-efficient}). Therefore, a new class of efficient algorithms is
set up that matchthe $\Omega(\log{(n)})$ time lower-bound established by
Kushilevitz and Mansour.
