Lecture 6 - What is colour?

Question 1

What is wavelength?

Answer 1

(m)- the distance from one point on a wave to the same point on the successive wave

Question 2

Whatis frequency?

Answer 2

(Hz)- how many waves go by in 1 second

Question 3

What is period?

Answer 3

(s)- how long a wave takes to go through the full range of motion

Question 4

What is light characterised by?

Answer 4

wavelength or its frequency

Question 5

What can looking at the colour of a wave do?

Answer 5

help determine its frequency

Question 6

What is black?

Answer 6

absorb all frequencies of light

Question 7

What are the different aspects of colour?

Answer 7

colour temp
blackbody radiator
non-blackbody radiators

Question 8

What does thermal sources of light do?

Answer 8

emit radiant energy in proportion to their temperature

Question 9

What does the colour tell us when it emits?

Answer 9

tells us the temperature of the source

Question 10

Where is the colour temperature commonly observed?

Answer 10

when a piece of metal is heated

Question 11

What happens when you increase the temperature of the flame to the metal?

Answer 11

the metal will start to glow red

and when its very hot it will turn white and blue

Question 12

What is a blackbody radiator?

Answer 12

• a perfect blackbody is a theoretical object that would absorb all the radiation/wavelengths that falls on it
• it would not reflect or transmit any radiation
• best possible emitter and absorber of radiation

Question 13

What are non-blackbody radiator?

Answer 13

white and shiny silvery surfaces which are poor emitters

Question 14

Why are radiators in home usually painted white?

Answer 14

so that the infrared radiation is emitted gradually

Question 15

What happens if you increase temp in the blackbody curves?

Answer 15

there is a shift in wavelengths emitted

there is a shift towards shorter wavelengths

Question 16

What can you call blackbody radiators?

Answer 16

if a particular source radiates energy following those wavelengths (blackbody curve)

Question 17

How can you specify a blackbody radiator?

Answer 17

by its colour temperature, in degrees Kelvin (K)

Question 18

What does it mean if you have a red (warm) lamp?

Answer 18

its colour temperature is LOW

Question 19

What does it mean if you have a cold (white) lamp?

Answer 19

it colour temperature is HIGH

Question 20

What do people prefer from home lamps?

Answer 20

a colder lamp which gives a warmer sensation/look(so red lamp)

Question 21

What do people prefer for work/office/school lamps?

Answer 21

a warmer lamp which gives a colder sensation/look (so white lamp)

Question 22

What system allows us to specify colours graphically?

Answer 22

CIE 1931 (x,y) colour space

Question 23

What does the CIE system do?

Answer 23

specify x,y,z co-ordinate on the chart- mixture of 3 CIE primaries called tristimulus values
they map a colour with respect to hue and saturation on a 2D CIE colour space

Question 24

What colour is more saturated?

Answer 24

the further away you are (to edges) the more saturated

Question 25

What are spectral colours?

Answer 25

one wavelength colour they are aligned around the outside of the horse-shoe shape and are most saturated can be correlated to a specific wavelength

Question 26

What colours are less saturated?

Answer 26

closer to the centre

Question 27

How can you make a colour?

Answer 27

by combining wavelengths | one colour can be made many different ways - from combinations of colours

Question 28

What is white light?

Answer 28

can be made of any mixture of different colours | in the middle of CIE spectrum

Question 29

What else is part of the CIE garph?

Answer 29

line of purples across the bottom.

Question 30

What else is part of the CIE garph?

Answer 30

line of purples across the bottom.

Question 31

What is additive colour mixing?

Answer 31

mixing lights of different wavelengths | superposition of red,blue,green lights which can be combined to make visibile light

Question 32

What are the primary colours?

Answer 32

red , green, blue which make whitw light

Question 33

What are the complementary colours for R,G,B?

Answer 33

Cyan magenta yellow

Question 34

What do computer monitors use?

Answer 34

additive colour mixing

Question 35

What is the triangle in the computer monitor?

Answer 35

the computer monitor can only produce those colours by mixing them in different combinations

Question 36

What do the 3 primaries in the computer monitor do?

Answer 36

produce the triangle

Question 37

What is the gamet determined by?

Answer 37

in chromaticity space, the gamet is determined by the triangle formed by the chromaticities of the light

Question 38

Maximum luminance?

Answer 38

determined by the sums of the R,G,B luminances

Question 39

What is a gamet?

Answer 39

all colours the display can produce

Question 40

What is subtractive colour mixing?

Answer 40

based on absorption or subtraction of certain wavelengths from white light. as a result of absorbing different wavelengths of colours

Question 41

What are the usual colours in colour printing?

Answer 41

cyan, magenta, yellow, black