Spectral indices measured between 54 and 144 MHz with LOFAR LBA and HBA respectively. The grey shaded areas show where the distribution becomes incomplete for flatter sources due to the varying sensitivity of the LBA observations, assuming a 5σ detection of a point source at the minimum (0.65 mJy beam⁻¹, light grey) and median (1.1 mJy beam⁻¹, dark grey) rms. The dotted line shows a value of −0.5 to guide the eye. The black points show the median values and errors on the median within equally spaced logarithmic flux-density bins, showing a flattening of spectra towards lower flux densities.