“Orthochromatic photography refers to a photographic emulsion that is sensitive to only blue and green light, and thus can be processed with a red safelight. The increased blue sensitivity causes blue objects to appear lighter and red ones darker. A cyan lens filter—which removes red light—can be used with standard panchromatic film to produce a similar effect.”
The following example shows how different kinds of light create different images:
this image of Megan Beckwith was made in 2013 but the computer rendereds the RGB image using measurements of red, green and blue light. The black and white image at the top used orthocromatic film which is sensitive to green light.