  We include gaseous continuum and line emission into our GALEV models for the
spectral and photometric evolution of Simple Stellar Populations (SSPs) for
various metallicities in the range 0.02 <= Z/Zsun <= 2.5. This allows to extend
them to significantly younger ages than before. They now cover the age range
from 4 Myr all through 14 Gyr. We point out the very important contributions of
gaseous emission to broad band fluxes and their strong metallicity dependence
during very early evolutionary stages of star clusters, galaxies or subgalactic
fragments with vigorous ongoing star formation. Emission-line contributions are
commonly seen in these actively star-forming regions. Models without gaseous
emission cannot explain their observed colors at all, or lead to wrong age
estimates. We use up-to-date Lyman continuum emission rates and decided to use
recent empirical determinations of emission line ratios relative to Hbeta for
subsolar metallicities. We justify this approach for all situations where no or
not enough spectral information is available to determine all the parameters
required by photoionization models. The effects of gaseous line and continuum
emission on broad band fluxes are shown for different metallicities and as a
function of age. In addition to the many filter systems already included in our
earlier models, we here also include the HST NICMOS and Advanced Camera for
Surveys (= ACS) filter systems.
