  In view of new experimental results that strongly suggest a non-zero
cosmological constant, it becomes interesting to revisit the Friedman-Lemaitre
model of evolution of a universe with cosmological constant and radiation
pressure. In this paper, we discuss the explicit solutions for that model and
perform numerical explorations for reasonable values of cosmological
parameters. We also analyse the behaviour of redshifts in such models and the
description of ``very large scale geometrical features'' when analysed by
distant observers.
