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Crash Course :: Colour :: What is Colour?

AGS_WhatIsColor_2

Colours, millions of them, have been all around us from the minute our eyes came into focus. Like most ubiquitous aspects of our lives we don’t tend to give colour much thought. It’s just there, a handy adjective to describe our clothing, our cars, the landscape. But what is colour exactly? And, of the many colours surrounding us what is there by chance and what’s there by deliberate choice?

WHAT IS COLOUR?
At it’s simplest colour is a property of light. Electromagnetic Radiation is a type of radiant energy that’s characterized by wavelengths that travel in synchronized oscillations of electric and magnetic fields. Scientists measure wavelengths in nanometers (nm) and when they measure between 400nm – 700nm they fall into what’s called the visible spectrum of light. Isaac Newton is credited with discovering and naming the spectrum in the 17th Century after conducting a series of experiments that involved passing white light through prisms.

Colour Wavelength Interval
Red ~ 700–635 nm
Orange ~ 635–590 nm
Yellow ~ 590–560 nm
Green ~ 560–520 nm
Cyan ~ 520–490 nm
Blue ~ 490–450 nm
Violet ~ 450–400 nm

Different types of light sources affect the way colours appear. Sunlight (white light) is an evenly distributed mix of all the spectrum’s colours but no form of man made light accurately reproduces sunlight. A look at the spectral power distributions of various light sources shows that incandescent lights tilt towards the yellow, orange and red side of the spectrum, LEDs distribution bulges through green, yellow and orange, and fluorescent bulbs spike at the blue, green and orange.

These are small but important distinctions, because the colour of an object is primarily dependent on the light sources in the surrounding environment and if the light changes the colour we perceive often ends up changing too.

THE COLOUR OF OBJECTS
Ok, so if colours are essentially light and sunlight is an evenly distributed mix of the spectrum why are certain objects different colours? Well, the colour of an object also has to do with the physical make up of that object and how it absorbs, reflects or scatters the light.

If the surface of an opaque object absorbs all the wavelengths it will appear black. If the object reflects the wavelengths with approximately equal strength the object will appear white. If it reflects some wavelengths and absorbs others it’ll appear yellow or blue or another colour in the spectrum. Translucent and transparent material will reflect and scatter most wavelengths resulting in a slight tint of colour.

While light is the essence of colour how we see and perceive colour is just as, (and sometimes more) important then the basic physics of how light and colour are created. We will look at how humans and machines see colour in the next installment of Crash Course.