Testing evolutionary synthesis models: Empirical feedback to model makers

Integrated spectra of star clusters are the best test beds for predictions of evolutionary synthesis models. We present spectral fits of star cluster using a variety of recent models. All models allow good spectral fits, but newer ones tend to be better. Ages estimated through spectral fits are not strongly model dependent, but metallicities can differ a lot from one model to another. For some clusters, multi-population fits suggest a combination of very old (10¹⁰ yr) and very young (< 10⁸) populations, an artifact of the lack of old and blue stars in the models.