The Colour of Light & The Colour of Objects

Colour by Addition Sir Isaac Newton first discovered that visible (white) light was made up of many colours – ROY G BIV. He could split visible light into its spectrum using a prism and then put it back together using a second prism.

Additive Colour Theory Additive Colour Theory states… You can mix red, green and blue light beams to make a white light beam. Red, green and blue are the primary colours of light. You can’t make them by blending other colours but you can use them to make many other colours. You can produce the secondary colours of light by mixing any two of the three primary colours. Many visual technologies (like TV’s, iPods) make use of the additive colour theory.

Secondary Colours Red + Blue = Magenta Red + Green = Yellow Green + Blue = Cyan

Complementary Colours Complementary colours of light are any two colours that can be added together to make white light. Each complementary pair is made of one primary colour and one secondary colour. Complementary pairs: –Green & Magenta (G + (R + B)) –Blue & Yellow (B + (G + R)) –Red & Cyan (R + [B + G])

The Colour of Objects

Colour by Subtraction What determines the colours of the objects around you? Objects can be opaque, translucent or transparent. –Opaque – solid and does not allow light to pass through it. –Translucent – allows some light through while scattering others. You can partially see through something that is translucent. –Transparent – allows all light to pass through it.

Examples Opaque Translucent Transparent

Subtractive Colour Theory When you see something, you actually are seeing the light that is reflected off of the object. White light from the Sun, or a light bulb, is hitting every object – but not every object is white. Why? Objects absorb some of the light that hits them and reflects some of that light as well. It is the combinations of absorbed light and reflected light that gives the object its colour.

Reflected Light

How We See Colours

Human Vision The human eye detects light and allows us to see. The retina, found at the back of the eye, contains millions of specialized cells called rods and cones. Rods are in charge of black and white vision. –When it gets dark outside – the rods take over. Cones look after colour. There are three types – red, blue and green.

The Eye

Who absorbs all light except green light? You knew I’d be back!!!