This paper discusses the possibility of detecting artificial illuminated objects in the outskirt of solar system by measuring the flux variation with respect to distance.
The authors begin by arguing that there are two basic illumination classes we use, one is thermal (light bulb) and the other one is quantum (LED). The spectra of those light sources should be very different from natural sources. Therefore, it is possible to detect those sources.
Further, the authors discuss whether we could detect those sources with our current technology and their conclusion is that we could be able to detect illumination level on the equivalent scale of large cities on Earth out to the outskirt of Solar system.
Additionally, the authors quantitatively calculate the flux versus distance slope difference between artificial objects (-2) and natural sources (-4). There are other factors that could affect this slope, including changing phase angle. Those factors influence the flux variation on the scale of 0.1 magnitude and should be able to be averaged out by long period of observation.
Finally, the authors argue that the chances of detecting such objects will be higher when the “dark side of the planet is more in view” or the host star of planet has went into a white dwarf so that the light contrast will be higher.