Land Effect

What is colour? For artists colour is an expression, a feeling, a memory, sometimes a taste or even a smell. Colour connects and expresses the intangible, the indescribable. It makes the everyday seem extraordinary and the extraordinary feel familiar.

      

What our brains perceive as colour is the reflection of wavelengths of light from objects.

In humans light is received by the eye where two types of photoreceptors, cones and rods, send signals to the visual cortex which in turn processes those sensations into a subjective perception of colour. (Wikipedia.org) 

Our ability to distinguish different objects and their various colours has to do with colour constancy.

Colour constancy is a process that allows the brain to recognize a familiar object as being a consistent colour regardless of the amount of light reflecting from it at a given moment. (Wikipedia.org)

Colour Constancy is why a white jacket still looks white instead of orange under the setting sun but like with other things the brain can be fooled. This fooling of the brain is commonly known as The Land Effect or Retinex Theory, devised by Edwin Land, made famous for his invention of instant photography and the Polaroid camera.

The Retinex theory first appeared in 1959, Scientific American magazine. The article claimed that it was possible to produce a full-colour image with only two component colours white and red. According to Land, we decide the colour of something by comparing its ability to reflect short, medium and long wavelengths with that of adjoining objects. Land considered that the eye and the brain (the retina and cortex) form a single optical system, which he called the retinex.

Have a look at the picture below, made available by grand-illusions.com. What colours do you see? Red, green, yellow, possibly brown? 

http://www.grand-illusions.com/acatalog/Land_Effect.html

In fact this is a demonstration of the Land Effect, since you are looking at a monochrome red image, with a black and white overlay. The only 'real ' colour here is red. However our brains tend to 'see' other colours being present. 

This experiment shows that even in reality colour is interpreted by our minds. It shows that our brains “fill in the picture”. An artist working in light and colour uses these perceptions like a great illusionist showing us the inner meaning of objects, connecting them with great ideas, and filling them with insight.