  We aim to gain insight into the effect of network and faculae on solar
irradiance from their apparent intensity. Taking full-disc observations from
the Solar Dynamics Observatory, we examined the intensity contrast of network
and 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 disc
centre, nearby magnetic fields, and time. The brightness of network and faculae
is believed to be suppressed by nearby magnetic fields from its effect on
convection. The difference in intensity contrast between the quiet-Sun network
and active region faculae, noted by various studies, arises because active
regions are more magnetically crowded and is not due to any fundamental
physical differences between network and faculae. These results highlight that
solar irradiance models need to include the effect of nearby magnetic fields on
network and faculae brightness. We found evidence that suggests that departures
from local thermal equilibrium (LTE) might have limited effect on intensity
contrast. This could explain why solar irradiance models that are based on the
intensity contrast of solar surface magnetic features calculated assuming LTE
reproduce the observed spectral variability even where the LTE assumption
breaks down. Certain models of solar irradiance employ chromospheric indices as
direct 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 contrast
measurements derived here, we show that the fluctuations in chromospheric
emission from network and faculae are a reasonable estimate of the emission
fluctuations in the middle photosphere, but not of those in the lower
photosphere. The data set, which extends from 2010 to 2018, indicates that
intensity contrast was stable to about 3% in this period.
