Colours of light can be added together to form a variety of colours Section 4.3 Lesson 5
How the eye sees colour • The cells of the eye can only detect three colours of the visible light spectrum: • Red • Blue • Green • These are known as the primarycolours of light • These colours combine to form all other colours
As you get further and further from the image on the screen you can finally see the eye. But note that the “colours” of the image are made up of different combinations of only three colours – red, green and blue, in each pixel of the image. Depending on how much of each colour is turned on these three colours can combine to form all the colours we see!
Cones cells detect colour (RBG) while rod cells detect variation of shades of colour Internal structure of the eye – notice that cone cells are located only at the back of the middle (macula) of the eye
Normal colour vision – cone cells help us see in colour but can only detect the red, green and blue parts of the visible light spectrum as seen below:
This is how a colour blind person sees “colours” because their cone cells do not work properly (they see in shades of grey).
Dysfunctions of the rods cells of the eye mean that all images are blurry Partial function of the cones (red only) means that all other colours are shades of grey.
Adding the colours of light • Because we only see red, green and blue colours of light, we need to “add” different amounts of these colours together in order to see all other colours • Think back to the image of the eye and the pixels earlier in this slide show • That is why we talk about mixing the colours as the “additive colours of light”
Additive Primary Colours Adding green creates two new secondary colours: Green + Red = Yellow Green + Blue = Cyan Magenta is a secondary colour – a mixture of red and blue Adding all three primary colours recreates white light
Combining Primary Additive Colours The three secondary colours – magenta, yellow and cyan - are also complementary to the primary colour opposite to each. Red is complementary to Cyan Blue is complementary to Yellow Green is complementary to Magenta
Red + Green + Blue = White R + G + B = W Primary colours Combining colours of light – colour equations Red + Green = Yellow R + G = Y Secondary colours Red + Blue = Magenta R + B = M Green + Blue = Cyan G + B = C
Colour blindness tests Normal – 45 Deficiency - nothing Normal = nothing CB - 45 Everyone Normal – 6 Deficiency - nothing Normal – 8 R/G = 3 Normal – 29 R/G = 70
Notes • Complete the Gizmo on Additive Colour of Light • Complete the first page of the handout • 4.3 How can you mix colours to make different colours? • Go on to Lesson 6 and the Gizmo before completing the rest of this handout.
Vocabulary Journal • Add these terms and definitions • primary colour • secondary colour • complementary colour