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
http://www.youtube.com/watch?v=gtgBHsSzCPE&feature=related
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!!!