To rephrase the question with an example, if light A puts out 50 lumens, and light B puts out 100 lumens, does B APPEAR to be twice as bright as A?[/quote]
I'm an ear doctor, not an eye doctor, but I can tell you that most of our senses work on log scales. Twice the sound or light energy is typically perceived as only a little bit more. When I went to medical school, I was taught that the human eye has a 100,000X sensitivity range. Our eyes and brains adjust so much that we can't rely them when it comes to hue or brightness for photography. Film more accurately captures the yellow of an incan or the green of a fluorescent light. And without a light meter, our photos would almost always be over or under exposed. I have the 070 C2 model and think it is very nice because it is bright and has a nice warm-white tint. Don't know for sure if I'll notice any increase in brightness, but I ordered the 100 model this past week.