Color Does Not Exist—Part 3

Detecting a target whose color may vary could impact optical or vision-system sensors and cameras. But what is color? When a strip of steel oxidizes and turns reddish brown or a copper-strip greenish, what is this color change? To answer this properly we need to understand something that I have been teaching for decades.

Isaac Newton was the first to discover that sunlight is made up of many colors even though the sunlight itself may appear to have no color of its own. He did this by passing the sunlight through a prism. Perhaps as a child you too may have experimented with a prism and discovered a rainbow of colors as it processed the sunlight. Further experimentation and much mathematics were performed by numerous physicists, including Albert Einstein, ultimately defining color in an unexpected and seemingly counterintuitive .

When you turn on a fluorescent light, the light coming out of the fluorescent tubes seems to be white and yet the room is full of colors. Let’s perform a mental experiment to make sense of this. Imagine that the room has some clothes scattered on the furniture. There is a red sweater, a blue pair of jeans and a yellow scarf. Our innate common sense informs us that the colors of the clothes are red, blue and yellow. But this is far from being so. As Einstein explained in his famous photoelectric paper (the one for which he received his one and only Nobel Prize), light from a fluorescent fixture, the Sun, a flashlight, etc., is made up of small particles (later named photons). The photons themselves have no color as they exit the light source. Rather, they vibrate at their own frequencies, with some photons vibrating relatively slowly and others much faster. This set of different vibrations is called the visible light spectrum.