How Everything Works
How Everything Works How Everything Works
 

QUESTIONS AND ANSWERS
 
Question 1357

Is the red light effect in xerographic copiers the same concept behind red lights in a darkroom? Does film have the same sort of properties?
Yes. The light sensitive particles in black-and-white photographic paper don't respond to red light because the energy in a photon of red light doesn't have enough energy to cause the required chemical change. In effect, electrons are being asked to shift between levels when the light hits them and red light can't make that happen in the photographic paper. However, most modern black-and-white films are sensitive to red light because that makes roses and other red objects appear less dark and more realistic in the photographs.
         

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