Colour & Filters

D. Crowley, 2008

Colour & Filters

To know how coloured filters work, and to be able to predict how these will affect the appearance of an object

Light Key Words

Solve the following anagrams of light key terms…

SuonmiulNno-minluousDepisrdesDetcfrareFerletcedEencidnciGlaneMsurtcpeRooluc

LuminousNon-luminousDispersedRefractedReflectedIncidenceAngleSpectrumColour

Colour

Look at the following colours – why do we seem them?

Coloured objects reflect some colours and absorb others

Red absorbs all colours, except red which it reflects

Green absorbs all colours, except green which it reflects

Blue absorbs all colours, except blue which it reflects

Black absorbs all light, reflecting none…

White reflects all light, absorbing none…

ObjectFilter

Colour

Now look at the following colours through a filter…

Filters let certain colours of light pass through, but absorb all other colours

Using the different filters look at the colours on the board / around the room and try and work out what the filter is doing – i.e. what is a blue filter doing? What about a red filter etc…

ObjectFilter

Colours

A red filter absorbs all colours…

A blue filter absorbs all colours…

A green filter absorbs all colours...

…apart from red light

…apart from blue light

…apart from green light

Colours

A magenta filter absorbs all colours…

A cyan filter absorbs all colours…

A yellow filter absorbs all colours...

…apart from red and blue light

…apart from green and blue light

…apart from red and green light

Light

Filters can make objects appear different colours than they actually are

This is because they only let a certain type of light through (e.g. red filter only lets red light through)

Looking through a red filter can therefore be described as looking at something in red light

Red light shines on the ball

The red ball reflects the red light, appearing red

Red Ball

What does a red ball appear like in different light, e.g. in green, blue and magenta light?

In green light

Green light shines on the ball

The red ball absorbs the green light, so no light is reflected, and the ball appears black

Red Ball

What does a red ball appear like in different light, e.g. in green, blue and magenta light?

In blue light

Blue light shines on the ball

The red ball absorbs the blue light, so no light is reflected, and the ball appears black

Red Ball

What does a red ball appear like in different light, e.g. in green, blue and magenta light?

In magenta light (mix of red and blue)

Magenta light shines on the ball

The red ball absorbs the blue light and reflects the red light, appearing red

Filter

Light Questions

Light Answers

Light cannot travel through a stone

Luminous source - lamp

Opaque object - desk, cup, book etc…

Transparent object - glass, window etc…

Light Answers

Box B

Normal

Light is dispersed in all directions