Lightroom shows me a "brightness value" for each of my photos:
I notice that it's negative for night photography and positive for daytime photos, but I don't know how it's computed. Is it the average or median pixel value in the image? In other words, an indication of where the photo falls in the spectrum between high- and low-key images?
Can I use the brightness value to compare images, or make them equally bright perceptually? Are there other uses for this value?