Why an Object Appears Violet in Sunlight

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To find out more about the diagram above . . . . read on!

Why an Object Appears Violet in Sunlight

Look carefully at the diagram at the top of the page. Now check out the following questions (and answers)!

  1. What natural source radiates light at all wavelengths of the electromagnetic spectrum?
  2. Does the sun produce light containing all wavelengths of the visible spectrum?
  3. What is the name for light containing all the wavelengths of the visible spectrum at equal intensity?
  4. Name the three RGB primary colours that can together produce white light?
  5. When white light strikes an object, what determines the colour an observer sees?

About the Diagram

Introducing the diagram! Read back and forward between the image at the top of the page and the explanation below!

This is one of a set of 10 diagrams exploring why objects appear to be different colours to an observer.

There are always three key factors that affect the colour of an object.

  • The first is the type of light source and what happens to the light on its journey towards an object.
  • The second is what happens when light strikes different types of objects and materials.
  • The third concerns factors related to the observer which affect what they see and how things appear.

When light strikes an object at least one of the following things happens:

  • Reflection. The term reflection refers to a situation where light strikes the surface of an object and some wavelengths are obstructed and bounce off. If the surface is smooth, light is reflected away at the same angle as it hits the surface. The term reflection refers then to what happens to wavelengths of light that are neither absorbed (by an opaque medium) nor transmitted (through a transparent medium).
  • Scattering. Scattering takes place when light waves are reflected in random directions at the boundary between two media. Scattering can also take place when light strikes particles or other irregularities within a medium through which light propagates.
  • Absorption. When light strikes an opaque medium the wavelengths that are not reflected are absorbed and their energy is converted to heat.
  • Transmission. In optics, transmission refers to the passage of electromagnetic radiation through a medium.
  • Refraction. The term refraction refers to the way a light wave changes direction and speed as it travels from one medium to another.
  • Dispersion. Chromatic dispersion refers to the way that light separates into its component wavelengths and the colours corresponding with each wavelength become visible.

To make sense of these diagrams it’s important to be clear about the following:

Light sources:

  • In the context of a discussion of visible light, a light source is a natural or man-made object that emits a range of wavelengths – each corresponding with a different colour.
  • The light source in these diagrams is the Sun.
  • Sunlight includes all visible wavelengths. The diagrams explore what happens to the wavelengths of ROYGBV. An arrow is used to represent each incident ray.
  • The diagram uses coloured balls to represent the object the incident rays strike. The wavelengths which are absorbed, reflected or transmitted (through the transparent ball) are shown by arrows.
  • The observer is represented by an eye and the colour of the object as seen by the observer is shown in a thought bubble.
  • Use the text to check exactly which colours are absorbed, reflected or transmitted.

Objects:

  • Every object, material, medium or substance that we can see is made of matter of one kind or another. The key differentiating factor is the elements and molecules they are constructed from.
  • You will have come across the elements that make up the periodic table.
  • A close look at molecules reveals that they are made up of atoms composed of electrons surrounding a nucleus of protons and electrons.
  • In a nutshell, different elements and molecules react to light in different ways because of their atomic structure and the particular way they combine to form mixtures or compounds.
  • In the case of an opaque object, it is the molecules that form its surface that determine what happens when light strikes it. Translucent and transparent objects behave differently because light can travel through them.
  • Another factor that needs to be taken into account when light strikes an object is surface finish. A smooth and polished surface behaves differently from one that is rough, textured or covered in ripples.

Observers:

  • There are many different factors that can influence an observer’s colour perception.
  • Perhaps the most important factor is the colour of nearby objects.
  • Another important factor is to do with the well-being of an observer. Health, medications, mood, emotions or fatigue can all affect the eye, vision and perception.
  • A further factor is the environment in which colours are observed, the type of object and colour associations.
  • Two different observers may see colour differently because of life experience including educational, social and cultural factors.

Other useful facts:

  • Material: The matter from which a thing is or can be made.
  • Material thing: Something formed or consisting of matter.
  • Matter: (in physics) That which occupies space and possesses mass as distinct from energy.
  • Medium: A substance that carries a wave (or disturbance) from one location to another.
  • Object: a material thing that can be seen and touched.
  • Substance: a particular kind of matter with uniform properties.

Follow the blue links for definitions . . . . or check the summaries of key terms below!

Some Key Terms

Move to the next level! Check out the following terms.

Light source

A light source is a natural or man-made object that emits one or more wavelengths of light. The Sun is ...
Read More

Observer

A human observer is a person who engages in observation or watches something. In the presence of light, an observer ...
Read More

Reflection

Reflection takes place when incoming light strikes the surface of a medium, obstructing some wavelengths which bounce back into the ...
Read More

ROYGBV

ROYGBV is an acronym for the sequence of hues (colours) commonly described as making up a rainbow: red, orange, yellow, ...
Read More

Visible spectrum

The visible part of the electromagnetic spectrum is called the visible spectrum. The visible spectrum is the range of wavelengths ...
Read More

Wavelength

Wavelength is a measurement from any point on the path of a wave to the same point on its next ...
Read More

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All slides share common specifications:

  • Titles: All slides have titles.
  • Backgrounds: Black, framed with a violet gradient.
  • Size: 1686 x 1124 pixels (3:2 aspect ratio).
  • Slides are available in two file formats: JPG, AI (Adobe Illustrator).

Slides are optimized for viewing on-screen or with a projector.
Diagrams are optimized for printing on A4 pages in portrait format.

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Diagram


All images on the lightcolourvision.org website are available for download as either slides or diagrams.

All diagrams share common specifications:

  • Titles: No titles.
  • Backgrounds: White.
  • Size: 1686 pixels wide. So all diagrams reproduce at the same scale when inserted into Word documents etc.
  • Labels: Calibri 24pt Italic.
  • Diagrams are available in two file formats: JPG, AI (Adobe Illustrator).

Diagrams are optimized for printing on A4 pages in portrait format.
Slides are optimized for viewing on-screen or using a projector.

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JPG file format


Download the image at the top of this page as a JPG file:

  • All JPG images available for download are 1686px wide.
  • Text on JPG images with white backgrounds is styled as Calibri 24pt Italic.
  • If the image you need is not exactly right, download it as an AI (Adobe Illustrator) file and edit it.
  • All the images on these Resource Pages were created in Adobe Illustrator and are vector drawings.

Did you know:

  • JPG stands for Joint Photographic Experts Group who created the standard.
  • The JPG file extension is used interchangeably with JPEG.
  • JPG files can be compressed for use on websites.
  • JPG files can be placed or pasted directly into MS Office documents.

FILE TYPES - AI

AI (Adobe Illustrator) file format


Download the image at the top of this page as an AI (Adobe Illustrator) file:

  • All AI images available for download from lightcolourvision.org are 1686px wide.
  • All the images on these Resource Pages were created in Adobe Illustrator and are vector drawings.
  • Vector drawing can be scaled up or down without any loss of quality.

Did you know:

  • AI  files downloaded from lightcolourvision.org can be re-edited using Adobe Illustrator for your own personal use.
  • Adobe Illustrator can save or export AI files to other formats including PDF (.pdf), PNG (.png), JPG (.jpeg) and SVG(.svg) etc.

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