Sunlight, candle-light and resistive filament lights (incandescent) have a broadband spectrum. Through most of history we've viewed the world lit by these sources.
Moving to fluorescent lights causes spectral quantisation as the frequencies are due to electronic band transitions in the gas. The phosphor absorbs and re-emits energy in different bands that fills out the spectrum but it's still really strange, with missing bits. When fluorescent lights first became popular people complained of headaches from the strange spectrum. They are disfavoured in certain industrial applications because they make some colours harder to see.
Semiconductor lighting is even worse in this regard. Radiative re-emission in valance holes emits line spectrums. Only by combining these do we trick the eye into seeing "white light". Recently we've got good at blending doping agents to give mixed spectrums that approximate daylight.
If these forms of electronic lighting have holes in their spectra, perhaps that's why an analysis of a corpus of photos shows a change in spectrum over time?