How  many  different  colours  did  you  mix  to  match  the  colour  of  your  classmate's  eye?  

When  given  the  choice,  we  like  to  pick  a  pencil,  bag  or  T-­‐shirt  in  the  colours  that  we  like.    Today,  we  take  it  o;en  for  granted  that  products  are  available  in  different  colours.  Chemists  have  worked  hard  to  find  molecules  (a  group  of  atoms  that  are  bound  together)  that  absorb  exactly  those  parts  of  white  light  that  will  produce  a  desired  colour.  And  they  have  found  many  ways  to  make  these  molecules  sEck  to  objects  so  we  see  them  with  colour:  paints,  inks,  dyes…

However,  it’s  not  that  easy  as  it  might  seem  to  colour  things,  especially  when  you  want  to  match  a  specific  colour  that  you  have  in  mind.  To  get  the  colour  right,  you  usually  have  to  mix  other  colours  in  exactly  the  right  proporEon.  In  this  worksheet,  we  will  explore  some  of  the  many  ways  to  do  this.  White  white  white  whiteWhite  white  white  whiteWhite  

white  white  white

My Name:

Get the colour rightWhat  is  your  favourite  colour?  How  do  you  make  it?

colours  |  mixing

To   illustrate   how   difficult   it   can   be   to   exactly  match   a   specific   colour,   try   to   copy   the   eye   colour  of  a  classmate.  The  iris,  the  coloured  ring  around  the  centre  of  our  eye,  serves  as  a  kind  of  gate  to  control  how  white  

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1/3Photonics  Explorer  |  WS  02.2  Colour  Mixing

much  light  enters  our  eye.  Everybody’s  iris  has  a  different  colour.  Some  might  look  very  similar,  but  research  has  shown  that  not  even  the  eyes  of  twins  are  idenOcal  –  every  iris  is  unique!

Choose   someone   in   your   class  whose  eye   colour   you  would   like   to   copy.  Use  any  painOng  technique  you  like  (water  colours,  felt  or  ink  pens,  crayons,  …)  and  try  to  match  the  colour  as  close  as  possible.  You  can  check  if  you  got  the  colour  right,  if  other  classmates  can  recognize  your  eye  model  based  on  your  artwork.

Now   have   a   look   at   the   photo   prints   in   your   schoolbooks.   A[er   your   experiment   above,   don’t   you   think   it   is  impressive  how  the  maker  of  this  book  manages  to  print  colours  that  accurately?  How  do  people  in  the  print  shop  do  this?  Take  a  closer  look  and  find  it  out  yourself!

Please  look  at  a  print  with  a  strong   magnifying  glass,  preferably  in  a  bright  region  of  the  picture.  What  do  you  noOce?  What  does  the  picture  actually  consist  of?

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How   do   you   make   white   in  a  print?   And   how   can   you   control   the  brightness  of  colours  in  a  print?

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What  do  you  think:  How  many  different  colours  are  used  to  mix  all  the  colours  that  you  see?  Can  you  guess  which  colours  these  are?  

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My Name:

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Use  the  magnifying  glass  to  look  at  a  white  pixel  in  a  display.  With  sufficient  magnificaOon  you  will  see  that  the  white  pixel  no  longer  

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Before  answering  these  quesOons,  we  will  study  another  complementary  way  of  mixing  colours.  Both  the  colours  you  used  to  paint  the  eye  and  the  colours  used  for  prinOng  absorb  parts  of  white  light.  Since  the  colour  of  light  depends  on  its  composiOon,  it  should  also  be  possible  to  combine  light  in  different  colours  to  create  a  new  colour.  Actually,  this  is  exactly  the  technique  used  in   colour  displays,  like  those  of  your  mobile  phone  or  laptop.  Use  your  magnifying  glass  again  and  find  out  how  this  works!

You  can  learn  a  lot  about  colours,  if  you  play  with  the  parameters  in  the  colour  selecOon  menu  and  try  to  understand  what  they  stand  for.  Can  you  make  out  a   connec7on  between  the  colours   in  the  table?  If  white

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colours  |  mixing

Photonics  Explorer  |  WS  02.2  Colour  Mixing

How  do  you  make  a  white  or  a  black  pixel  on  a  screen?  7

How  does  a  screen  vary  the  brightness  of  colours?8

appears  to  be  white.  Please  use  crayon  here  on  the  le[  hand  side  to  show  what  you  see:

Locate   the  menu   for   selecOng   colours   in   some   graphics   so[ware   on   a   computer.   Play  with   the   different  colour  mixing   parameters   and   look   at   the   resulOng   colour  with   the  magnifying   glass.   Then   generate   the  ennnnn

9colours  named  in  the  table  and  make  a  note  here  of  the  parameters  you  used.

colour

red

green

blue

cyan

magenta

yellowColour-­‐picking  menu  of  a  photo  edi<ng  so=ware  

you  have  an  idea,  think  of  an  experiment  to  provide  evidence  for  your  opinion.

My Name:

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Almost  all  photos  and  pictures  you  see  printed  in  books,  on  posters,  or  on  product  packaging  in  your  supermarket  are  printed   with   ink   in   black   and   merely   three   colours:   cyan,  magenta,   and   yellow.   By  mixing   just   these   three  colours,  you  can  create  the  full  spectrum  of  colours  you  see  on  prints  everywhere  around  you.

On   the   other   hand,   you   saw   that   the   screen   of   your   computer   or   mobile   phone   mixes   colours   for   each   pixel   by  controlling  the  brightness  of  Ony  light  sources  in   red,  green,  and  blue.  Why  do  you  use  red,  green  and  blue  to  mix  colours  by  adding  light,  but  use  cyan,  magenta  and  yellow  when  you  mix  colours  by  absorbing  light?  The  work  with  the  colour  selecOon  menu  in  Point  8  has  probably  given  you  a  clue.  Here  are  some  more  experiments  that  shed  light  on  this:

colours  |  mixing

Photonics  Explorer  |  WS  02.2  Colour  Mixing

Place   a  white   sheet   of   paper   on   the   table   and   sort   the   colour  filters  on   it   into   two  groups:  1)   cyan,  magenta,   yellow;   2)   red,   green,   blue.   Take   the   first   group   and   test   all   possible   combinaOons   of   filters.  whitewhite  

11What  colours  can  you  generate?  Compare  your  mixing  results  with  the  filters  in  the  second  group.  

Cyan and magenta:Cyan and yellow:yellow and magenta:yellow, magenta and cyan:

Now  test  all  combinaOons  of  two  filters  from  the  second  group.  What  differences  do  you  note  compared  to  the  previous  experiment?

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Ask  your  teacher  for  a   LED  module  and  aiach  it  to  the  baiery.  Find  out  how  you  can  switch  on  all  three  colours  at  the  same  Ome  and  shine  the  light  on  the  white  sheet  of  paper.  Then  take  the  magnifying  glass  white  

13and  place  it  between  the  light  source  and  the  paper,  so  that  the  three  colours  appear  as  unsharp,  overlapping  discs.  Which  colour  appears  at  the  centre?  Can  you  explain  why?

Test   all   combinaOons   of   the   three   colours   and   note  below   what   colour   you   see   where   the   lights   mixing  nnnnn  white

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blue and green:blue and red:red and green:red, green and blue:

What   do   you   conclude   from   the   experiments   on   this   page   about   the   relaOonships   between   the   6  colours?  Can  you  explain  why  you  use  red,  green  and  blue  for  screens,  but  cyan,  magenta  and  yellow  for  prinOng?

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together  have  about  the  same  strength.