  We investigate gathering algorithms for asynchronous autonomous mobile robots
moving in uniform ring-shaped networks. Different from most work using the
Look-Compute-Move (LCM) model, we assume that robots have limited visibility
and lights. That is, robots can observe nodes only within a certain fixed
distance, and emit a color from a set of constant number of colors. We consider
gathering algorithms depending on two parameters related to the initial
configuration: $M_{init}$, which denotes the number of nodes between two border
nodes, and $O_{init}$, which denotes the number of nodes hosting robots between
two border nodes. In both cases, a border node is a node hosting one or more
robots that cannot see other robots on at least one side. Our main contribution
is to prove that, if $M_{init}$ or $O_{init}$ is odd, gathering is always
feasible with three or four colors. The proposed algorithms do not require
additional assumptions, such as knowledge of the number of robots, multiplicity
detection capabilities, or the assumption of towerless initial configurations.
These results demonstrate the power of lights to achieve gathering of robots
with limited visibility.
