1. How do we see Colour?

2. When you think of colour, you probably think of the colours of the crayons you used in kindergarten…
Red
Yellow
Blue
Red, yellow and blue are pigment colours.

3. A pigment is a chemical that interacts with light, absorbing certain wavelengths of light, and reflecting other wavelengths. The reflected wavelengths are the colours we see. Pigments are what give crayons and paints and inks their characteristic “colours.”
Yellow
Red
Blue

4. The primary pigment colours are red, yellow and blue.
These primary colours can be mixed together in different combinations to make secondary pigment colours: orange, green and purple.
Orange
Yellow
Red
Purple
Green
Blue

5. When you mix pigment colours together, they become darker and reflect less light. For this reason, pigment colours are called subtractive colours.
Orange
Yellow
Red
Purple
Green
Blue

6. The primary colours of light are red, green and blue
The primary colours of light are red, green and blue. These colours are caued by different wavelengths of visible light.
Red has long wavelengths
Green has medium wavelengths
Blue has short wavelengths
Blue
Green
Red

7. Yellow
The primary colours of light can be mixed together in different combinations to make secondary colours: cyan, magenta and yellow.
Red
Green
Cyan
Magenta
When you mix all three primary colours together, they make white light.
Blue

8. Yellow
The colours of light are called additive colours. When you mix them together, they become brighter as more light is emitted.
Red
Green
Cyan
Magenta
Blue

9. Time for a quiz….. Get out your plickers!

10. Let’s play with coloured lights

11. How does your eye detect colour?

12. or
Retina remnants
Retina

13. Cone
Retina close-up
Rod 3
Light 1 2 1
Epithelial Cell 4 5
Blind Spot

14. Find your blind spot!

15. The retina is made up of 2 kinds of light-sensing cells:

16. Rods
around the outside of the retina
sensitive to light and dark
Retina

17. Cones
in the centre of the retina (the fovea)
sensitive to different wavelengths (colours) of light
Retina

18. Humans have 3 types of cones:
“red” cones - sensitive to long wavelengths
“green” cones - sensitive to medium wavelengths
“blue” cones - sensitive to short wavelengths

19. note: the cones themselves are not coloured!!!
they are just sensitive to certain colours (wavelength) of light

20. Note that each type of cone can perceive a wide range of wavelengths (colours) but has a peak of sensitivity

21. Scientists refer to the cones as
long wavelength cones
medium wavelength cones
short wavelength cones

22. Note also that “red” cones actually peak in the yellow area of the spectrum!!!
What’s with that?

23. How does your brain know what colour you are seeing?

24. The brain compares the information it receives from the different types of cones, and uses that to decide what colour you are seeing

25. if the red cones detect a lot of light
but the green and blue cones detect none
the brain interprets this as red

26. if the red and green cones both detect equal amounts of light
but the blue cones detect none
the brain interprets this as yellow

27. if the red and green cones detect no light
but the blue cones detect a lot of light
the brain interprets this as blue

28. Afterimage

29. What about the rods?

30. if the rods detect high intensity (bright) light
the brain interprets this as a light colour

31. if the rods detect low intensity (dim) light
the brain interprets this as a dark colour

32. Yellow
So the colour you see is a result of the way your brain interprets the combination of
the wavelengths of light detected by the cones
the intensities of light detected by the rods
Red
Green
Cyan
Magenta
Blue

33. What does this quote mean?
“Color vision is an illusion created by the interactions of billions of neurons in our brain. There is no color in the external world; it is created by neural programs and projected onto the outer world we see.”
Peter Gouras, WebVision