Reconstructions of Lyman-α irradiance variations from Ca II K observations compared to the composite of Lyman-α observations by Machol et al. (2019). In particular, we show the semi-empirical SATIRE-Ca (see Sect. 3.2) reconstruction from Rome/PSPT (orange) and San Fernando (SFO; green) data by Chatzistergos et al. (2021a), as well as the empirical reconstructions (see Sect. 3.1) by Johannesson et al. (1995, purple) and Johannesson et al. (1998, red) from Big Bear solar observatory (BBSO) data, as well as by Worden et al. (2001, ciel) from Sac Peak data. All series are shown as 180-day running means. The numbers in the lower part of the figure denote the conventional solar cycle numbering.