>>3901150You might be thinking of how under/over exposure shows up on the negative. An overexposed shot (which is indeed more light) shows up as a darker, more dense image on the negative, and an underexposed image will be lighter. This is simply because the film has reacted more strongly to the shot with more light. When you print the negative into a positive, or scan it and flip it on the computer, light and dark are the right way round again.
E.g. these are (crops of) the same image, except the left one was a stop overexposed, so it shows up as more dense on the negative.