  We study chaotic synchronization in networks with time-delayed coupling. We
introduce the notion of strong and weak chaos, distinguished by the scaling
properties of the maximum Lyapunov exponent within the synchronization manifold
for large delay times, and relate this to the condition for stable or unstable
chaotic synchronization, respectively. In simulations of laser models and
experiments with electronic circuits, we identify transitions from weak to
strong and back to weak chaos upon monotonically increasing the coupling
strength.
