Unexpectedly I found two books on my desk recently from the “Little Technical Company” published in 1939. Perusing the pages of “Filters and Their Uses” it gave graphs of the light sensitivity of different films of the time but also included the human eye. I knew from the past that the human eye was not as sensitive to red or violet as the other colors but I had no idea that it was most sensitive to yellow. In fact it specifies that the light sensitivity of the human eye to visual light follows a bell curve (my term) and precipitously falls off outside the 500 to 600 angstroms of visual light. Visual light, the light the human eye can see starts at 400 angstroms and goes to 700 angstroms. Film does not follow this sensitivity, and I doubt does the sensor in digital cameras. Just a passing thought.