Globular Clusters ( GCs ) are generally treated as natural validators of simple stellar population ( SSP ) models .
However , there are still some differences between real GCs and SSPs .
In this work , we use a direct N -body simulation code Nbody6 to study the influences of dynamical interactions , metallicity and primordial binaries on Milky Way GCs ’ integrated properties .
Our models start with N = 100 , 000 stars , covering a metallicity range Z = 0.0001 \sim 0.02 , a subset of our models contain primordial binaries , resulting in a binary fraction as currently observed at a model age of GCs .
Stellar evolution and external tidal field representative for an average Milky Way GC are taken into consideration .
The integrated colours and Lick indices are calculated using BaSeL and Bluered stellar spectral libraries separately .

By including dynamical interactions , our model clusters show integrated features ( i.e. , colours up to 0.01mag bluer , H \beta up to 0.1Å greater and [ MgFe ] ^ { \prime } 0.05Å smaller ) making the clusters appear slightly younger than the model clusters without dynamical interactions .
This effect is caused mainly by the preferential loss of low-mass stars which have a stronger contribution to redder passbands as well as different spectral features compared to higher-mass stars .
In addition , this effect is larger at lower metallicities .
On the contrary , the incorporation of primordial binaries reduces this effect .