Jacques ValléeVallee, Jacques: J. Scientific Exploration, Vol. 12, n° 3, pp. 345-358, September 1998

Some of the most striking statements made by witnesses of unusual aerial objects during their debriefing by investigators have to do with the luminosity of the phenomenon. They frequently use expressions like it lit up the whole landscape or every object in the area stood out, intensely thrown into relief. Beyond these subjective statements (which could be affected by physiological and psychological factors) it is difficult to obtain reliable quantitative data on the power output of the observed objects. Typically the witnesses are surprised by the phenomenon and it is rare for them to have any basis of comparison or calibration. A few such cases do exist, however, and a special effort has been made here to derive estimates from the data.

Obvious cautions are immediately raised by this exercise. By definition the source of the luminosity is an unknown phenomenon. We do not know if the light is a primary manifestation of its internal physical state (as would be the case for the sun) or a secondary one, as would be the case for the moon or an automobile headlight. We do not even know if most of the electromagnetic energy is released in the visible domain to which human witnesses and most cameras react.

Given these cautions one can, at best, hope to bracket a physical range to characterize the phenomenon in question. More relevant than the actual numerical values obtained in a few cases is the methodology involved in acquiring and processing such parameters.