The slopes of JHK_s PLRs for RRc, RRab, and global sample of all RRLs in GCs of different mean metallicities. The slopes are taken from the following studies: M15 ([Fe/H] ∼ −2.33 dex, Bhardwaj et al. 2021b), M53 ([Fe/H] ∼ −2.06 dex, Bhardwaj et al. 2021a), ω Cen ([Fe/H] ∼ −1.64 dex, Braga et al. 2018), M3 ([Fe/H] ∼ −1.50 dex, Bhardwaj 2020), M4 ([Fe/H] ∼ −1.18 dex, Braga et al. 2015), and NGC 6441 ([Fe/H] ∼ −0.45 dex, this work). The increase in symbol size represents an increase in the dispersion in the PLRs. The shaded (gray) lines represent the slopes of the theoretically predicted PLZ relations from Marconi et al. (2015). The dashed lines represent the median value of slopes in each panel.