The phrase "irradiance changes" means the amount of light or energy that is being received or emitted by a surface, which can vary or fluctuate over time.
A model of solar irradiance variations is presented which is based on the assumption that solar surface magnetism is responsible for all total irradiance changes on time scales of days to years. (aanda.org)
Amplification of the direct solar forcing is conceivable, e.g., through effects on ozone or atmospheric condensation nuclei, but empirical data place a factor of two upper limit on the amplification, with the most likely forcing in the range 100 — 120 % of the directly measured solar irradiance change [64]. (journals.plos.org)
The other theme was the discussion of the spectral irradiance changes — specifically by how much the UV changes over a solar cycle are larger in magnitude than the changes in the total irradiance. (realclimate.org)