Color in Non-White Light

In class this week, we talked about how the human eye perceives color based on what wavelengths of white light are reflected from an object. However, what if the light that is hitting the object isn’t white to begin with? As mentioned at the beginning of Light Science Ch. 6, we determine color not just by looking at the object but also by considering the light hitting the object.

Noon-time sunlight is indeed white, but during sunset or twilight the light reflecting off of things isn’t white anymore. This also true of electrical lighting, which can be tinted blue, yellow, or other colors. We can still tell the color of objects under these sorts of light because our brains have adapted in a way that lets us take into account our surroundings when viewing an object. For example, if something looks magenta during blue-lit twilight hours, your brain knows to subtract the blue light and comes to the conclusion that the object would be red in white light, so your brain concludes the object is more likely red than magenta.

This phenomenon – our brain’s interpretation of the surrounding lighting, and how that affects our interpretation of an object’s color – is what led to the dress fiasco earlier this year, as discussed by Prof. Conway in the talk we went to a few weeks back. Many people saw what their brains interpreted as a blue and black dress under yellow-ish lighting, and many others saw a white and gold dress under blue-ish lighting. How can these be the same photo? It’s because some people thought the lining on the dress was shiny gold with black shadows, and others thought it was matte black with yellow highlights from the yellow lighting. Likewise, some thought the blue dress was mostly unaffected by the yellow lighting, while others though the white dress looked blue-ish because of blue lighting.

The most interesting part of this phenomenon is that it is entirely unconscious – we don’t notice our brains making these subtractions and interpretations. We only see a color, and don’t bother to think about whether our brains might have miscalculated.