Lecture 6 - What is Colour Flashcards
What is colour
Wavelength of light
What is wavelength
distance between 2 peaks on same wave
What is frequency
the number of complete waves generated per second
What is period
How long a wave takes to go through the full range of motion
What is light characterised by
Light is characterised by its wavelength or its frequency
Colour temperature
- Thermal sources of light emit radiant energy in proportion to their temperature - commonly observed when piece of metal is heated
What happens when a piece of metal is heated
It changes colour
What colour does the metal glow when temperature increases and how
Red
Emit light - radiant energy - heat - glows red
What colour is very hot
Blue
What is a blackbody radiator
Perfect blackbody - theoretical object ( not exist in reality )
What does a blackbody radiator do
ABSORB all radiation that falls on it - it would not reflect or transmit any radiation
Best emitter of radiation
Does a blackbody radiator absorb or reflect
Absorb
What is an example of a blackbody radiator and why
Stars
Blackholes
Good at absorbing all wavelenghts, but not perfect
What is property of something that is NOT a blackbody radiator
- White/shiny silver surfaces
- Worst absorbers
- Poor emitters
- Best reflecters
Example of something that is NOT a blackbody radiator and why
Radiators
Painted white - infrared radiation is emitted gradually - poorly - emit heat slowly
Link between temperature and wavelength
Increase in temp = shorter wavelengths
As temp increases, there’s a shift in wavelengths emitted
What is the shorter wavelength
Blue
What can a blackbody be specified by
Its colour temperature
What source is at a temp of 3000K
Warm white compact fluorescent and LED lamps
What source is at a temp of 5000K
Cool white fluorescent lamps ( hotter temp but cooler )
Colour temp and sensation link
Higher colour temp ( warmer ) - colder sensation
What is CIE ( x,y) Colour Space
Specifies colours graphically using x,y co-ordinates
If its closer to centre is it more or less saturated and what is the colour
Closer to centre - less saturated - white
If its further from edges ( chart ) it more or less saturated
More saturated
The co - ordinates x,y map the colour with respect to what
Hue and saturation
What are the spectral colours
Correlated to a specific wavelength
Where is the lines of purples located
Along bottom
How can achromatic colour also be achieved
With many different mixtures of light
What is additive colour mixing
- Mixing of light
- Superposition of RED, GREEN and BLUE lights
- Almost all visible colours can be obtained by additive colour mixing of 3 colours
- Involves primary colours
What is cyan
Red
What is magenta
Green
What is tello
Blue
Where is additive colour mixing used
Computer monitors
What are the 3 primary colours and what colour do they produce when mixed
Red, green, blue
Produce white
What is subtractive colour mixing
Colours created by partially/completely subtracting ( absorbing ) some wavelengths of light and not others
Where is subtractive colour mixing used
Coloured pigments, dyes, paints, inks
In colour printing what are usually the primary colours
Cyan, Magenta, Yellow and Black
