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We describe and summarize the findings from our CCD time-series photometry ofglobular clusters (GCs) program and the use of difference image analysis (DIA)in the extraction of very precise light curves even in the crowded centralregions down to $V\sim 19$ mag. We have discovered approximately 250 variablestars in a sample of 23 selected GCs and have, therefore, updated the census ofvariables in each system and in some cases we have actually completed it downto a certain magnitude. The absolute magnitude and [Fe/H] for each individualRR Lyrae is obtained via the Fourier decomposition of the light curve. Anaverage of these parameters leads to the distance and metallicity of the hostGCs. We have also calibrated the P-L relation for SX Phe stars which enables anindependent calculation of the cluster distance. We present the mean [Fe/H],$M_V$ and distance for a group of selected GCs based exclusively on the RRLyrae light curve Fourier decomposition technique and set on a ratherunprecedented homogeneous scale. We also discuss the luminosity dependence ofthe horizontal branch (HB) via the $M_V$-[Fe/H] relation. We find that thisrelation should be considered separately for the RRab and RRc stars.

CCD time-series photometry of variable stars in globular clusters and the metallicity dependence of the horizontal branch luminosity