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We aim to gain insight into the effect of network and faculae on solarirradiance from their apparent intensity. Taking full-disc observations fromthe Solar Dynamics Observatory, we examined the intensity contrast of networkand faculae in the continuum and core of the Fe I 6173 {\AA} line and 1700{\AA}, including the variation with magnetic flux density, distance from disccentre, nearby magnetic fields, and time. The brightness of network and faculaeis believed to be suppressed by nearby magnetic fields from its effect onconvection. The difference in intensity contrast between the quiet-Sun networkand active region faculae, noted by various studies, arises because activeregions are more magnetically crowded and is not due to any fundamentalphysical differences between network and faculae. These results highlight thatsolar irradiance models need to include the effect of nearby magnetic fields onnetwork and faculae brightness. We found evidence that suggests that departuresfrom local thermal equilibrium (LTE) might have limited effect on intensitycontrast. This could explain why solar irradiance models that are based on theintensity contrast of solar surface magnetic features calculated assuming LTEreproduce the observed spectral variability even where the LTE assumptionbreaks down. Certain models of solar irradiance employ chromospheric indices asdirect indications of the effect of network and faculae on solar irradiance.Based on past studies of the Ca II K line and on the intensity contrastmeasurements derived here, we show that the fluctuations in chromosphericemission from network and faculae are a reasonable estimate of the emissionfluctuations in the middle photosphere, but not of those in the lowerphotosphere. The data set, which extends from 2010 to 2018, indicates thatintensity contrast was stable to about 3% in this period.

Intensity contrast of solar network and faculae -- II. Implications for solar irradiance modelling