Illustration of the effect of stellar metallicity on EW(Hα). upper panel: Evolution of EW(Hα) for SFH models involving continuous SF at a constant SFR (dots), and exponentially decreasing SFR with an e-folding time of 0.1 Gyr and 1 Gyr (solid and dashed curve, respectively). Predictions from PéGASE 2 (Fioc & Rocca-Volmerange 1997) refer to a fixed stellar metallicity of Z_⊙, Z_⊙/5 and Z_⊙/20 (red, green and blue, respectively) and a Salpeter IMF between 0.1 and 100 M_⊙. lower panel: Ratio between the EW(Hα) for subsolar- and solar-metallicity models as a function of age. At an age of ∼16 Myr subsolar metallicity models imply a by a factor of up to ∼2 larger EW(Hα) than solar metallicity models.