  Binary stars are common in star clusters and galaxies, but the detailed
effects of binary evolution are not taken into account in some colour-magnitude
diagram (CMD) studies. This paper studies the CMDs of twelve globular clusters
via binary-star stellar populations. The observational CMDs of star clusters
are compared to those of binary-star populations, and then the stellar
metallicities, ages, distances and reddening values of these star clusters are
obtained. The paper also tests the different effects of binary and single stars
on CMD studies. It is shown that binaries can fit the observational CMDs of the
sample globular clusters better compared to single stars. This suggests that
the effects of binary evolution should be considered when modeling the CMDs and
stellar populations of star clusters and galaxies.
