What color would a red object look if you shined only green light on it and Why?

Answer 1

Assuming normal color vision for the observer, a red object in red light appears red. But that's so obvious that I suspect there may be another unstated context for the question. For example, if you are photographing an object with a panchromatic black and white film, you will get different results in different lighting. Since an object reflects its own color and absorbs others, a red object in blue or green light would be less or non-reflective, so will appear very dark in a photographic print. In red light (because it reflects red), it will appear light. That same principle of reflection and absorption explains why, in some very old photographs made with films that were not sensitized to red wavelengths, women wearing red lipstick appeared to have very black lips. The red was reflected, but made no exposure on the red-blind film. There may be other contexts for the question, but this should give you an idea how to treat them.

Answer 2

A 'red' object appears red because when a mixture of many colors of light shines on it, it absorbs most of them, and reflects mainly the red back off of it.

When illuminated by monochromatic yellow light, the object will appear black or very dark, since there is no incident red available, the yellow is mostly absorbed, and the total light level reflected off the surface is zero or very low.

Answer 3

A red object would appear black if only green light is shined on it because the object absorbs the green light and does not reflect any light back to our eyes. The object appears red under white light because it reflects red light and absorbs other colors.

Answer 4

Brown because the green light fragments bouncing off of the red object would be so rapid that, to the human eye, will look brown.