Solar radiation over and under sea ice was measured by radiation station 2018R23, an autonomous platform, installed on land fast ice in the Lincoln Sea, Arctic Ocean during Alert_MAPLI18. The resulting time series describes radiation measurements as a function of place and time between 05 May 2018 and 25 May 2018 in sample intervals of 10 minutes. The radiation measurements have been performed with spectral radiometers. All data are given in full spectral resolution interpolated to 1.0 nm, and integrated over the entire wavelength range (broadband, total: 320 to 950 nm). Two radiometers measuring solar irradiance and upward reflected solar irradiance, were mounted on a platform about 1 m above the sea-ice surface. The third radiometer was mounted 0.5 m underneath the sea ice measuring the downward transmitted irradiance. All times are given in UTC.