We perform integrated spectroscopy of 24 Galactic globular clusters .
Spectra are observed from one core radius for each cluster with a high wavelength resolution of \sim 2.0 Å FWHM .
In combination with two existing data sets from Puzia et al .
( 34 ) and Schiavon et al .
( 36 ) , we construct a large database of Lick spectral indices for a total of 53 Galactic globular clusters with a wide range of metallicities , -2.4 \lesssim [ Fe / H ] \lesssim 0.1 , and various horizontal-branch morphologies .
The empirical index-to-metallicity conversion relationships are provided for the 20 Lick indices for the use of deriving metallicities for remote , unresolved stellar systems .