# Wavelengths from Red to Violet

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## Description

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

#### Wavelengths from Red to Violet

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

1. Is visible light a form of electromagnetic radiation?
2. Do different wavelengths of light correspond with different colours?
3. Can you estimate how many different rays of colours are shown in the diagram above?
4. Name two colours with the longest wavelengths?
5. Name two colours with the shortest wavelengths?

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

This diagram is about which wavelengths of electromagnetic radiation correspond with the different colours we see in the world.

The important fact to remember is that the wavelengths of light within the visible spectrum correspond with all the colours that we see between red and violet.

• The white arrows in the diagram show the Sun emitting sunlight at all wavelengths of the visible spectrum.
• The term white light is used when all colours of the visible spectrum are mixed together.
• The spectrum of colours between red and violet illustrates that although an observer will often describe visible light (a rainbow for example) as six bands of colour, each and every wavelength between 700 and 430 nanometres is a different colour.
• The list on the left shows the range of wavelengths corresponding with each band of colour.
• The red arrow, for example, corresponds with wavelengths between 700 nanometres and 620 nanometres. Red is the colour an observer sees if any wavelength in that range strikes a neutral coloured surface.
• The scale along the bottom is marked in nanometres and shows the visible spectrum divided into coloured bands.

Remember that:

• Objects appear to be different colours to an observer depending on their wavelength.
• The name given to light that contains all wavelengths of the visible spectrum is white light.
• When all wavelengths contained in white light reflect off a neutral coloured surface then the object appears white to an observer.
• When a narrow band of wavelengths reflect off a neutral coloured surface then the object appears coloured to an observer.
• The colour an observer sees depends on the wavelengths of visible light emitted by a light source and on which of those wavelengths are reflected off an object.
• Although a human observer can distinguish between many thousands of wavelengths of light in the visible spectrum our brains often produce the impression of bands of colour.

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.

#### Colour

Things appear coloured because colour corresponds with a property of light that is visible to the human eye. The visual experience of colour is associated with words such as red, blue, yellow, etc.

• The experience of colour is a feature of human vision that depends first of all on the construction of our eyes and the wavelength, frequency and amplitude of visible light that strikes the retina at the back of each eye.
• The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. It is the sensitivity of the eye to this small part of the electromagnetic spectrum that results in the perception of colour.
• The colour an observer sees depends on the wavelengths of visible light emitted by a light source and on which of those wavelengths are reflected off an object.
• Although a human observer can distinguish between many thousands of wavelengths of light in the visible spectrum our brains often produce the impression of bands of colour.

Electromagnetic radiation is a type of energy that is commonly known as light. Detached from its source, it is transported by electromagnetic waves (or by their quanta, particles called photons) and propagates through space.

• Electromagnetic radiation includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.
• All forms of electromagnetic radiation can be described in terms of both waves or particles.
• All forms of electromagnetic radiation travel at 299,792 kilometres per second in a vacuum.

#### Sunlight

Sunlight is light emitted by the Sun and is also called daylight or visible light.

#### Visible light

Visible light is a form of electromagnetic radiation.

• Visible light is the range of wavelengths of electromagnetic radiation that are perceived as colour by a human observer.
• The range of wavelengths that produce visible light is a very small part of the electromagnetic spectrum.
• Other forms of electromagnetic radiation include radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
• Visible light is perceived by a human observer as all the spectral colours between red and violet plus all the other colours that result from mixing them together in different proportions.
• The complete range of colours that can be perceived by a human observer is called the visible spectrum.

#### Visible spectrum

The visible part of the electromagnetic spectrum is called the visible spectrum.

• The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
• As light travels through the air it is invisible to our eyes.
• Human beings don’t see wavelengths of light, but they do see the spectral colours that correspond with each wavelength and colours produced when different wavelengths are combined.
• The visible spectrum includes all the spectral colours between red and violet and each is produced by a single wavelength.
• The visible spectrum is often divided into named colours, though any division of this kind is somewhat arbitrary.
• Traditional colours referred to in English include red, orange, yellow, green, blue, and violet.

#### Wavelength

Wavelength is a measurement from any point on the path of a wave to the same point on its next oscillation. The measurement is made parallel to the centre-line of the wave.

#### white light

White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities.

• As light travels through a vacuum or a medium it is described as white light if it contains all the wavelengths of visible light.
• As light travels through the air it is invisible to our eyes.
• When we look around we see through the air because it is very transparent and light passes through it.
• The term white light doesn’t mean light is white as it travels through the air.
• One situation in which light becomes visible is when it reflects off the surface of an object.
• When white light strikes a neutral coloured object and all wavelengths are reflected then it appears white to an observer.

#### Slides

• Titles: All slides has titles.
• Backgrounds: Black, framed with a violet gradient.
• Size: 1686 x 1124 pixels (3:2 aspect ratio).
• Slides are available in three file formats: SVG, PNG, AI.

Slides (black backgrounds) are optimized for viewing on screen or with a projector.

Diagrams (white/transparent backgrounds) are optimized for printing on A4 pages in portrait format.

#### Diagrams

• Titles: No titles.
• Backgrounsd SVG: White.
• Backgrounsd PNG: Transparent.
• Backgrounds AI: Fully editable.
• 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 three file formats: SVG, PNG, AI.

Diagrams (white/transparent backgrounds) are optimized for printing on A4 pages in portrait format.

Slides (black backgrounds) are optimized for viewing on screen or using a projector.

#### SVG file format

• Text on SVG images with black backgrounds has been converted from fonts to outlines.
• Text on SVG images with white (or transparent) backgrounds use Calibri 24pt Italic.

Did you know:

• SVG (.svg) stands for Scalable Vector Graphic.
• SVG files scale up or down without loss of definition because they are like line drawings.
• SVG files are much smaller in size than most other file formats (e.g JPEG or PNG).
• You can insert SVG files directly into MS Word 365 or PowerPoint 365.
• You can view SVG files by dragging the file into a browser tab.
• You can edit SVG files using programs such as Adobe Illustrator.

#### PNG file format

• Because all images are a standard width they reproduce consistently on an A4 page.

Did you know:

• PNG (.png) stands for Portable Network Graphics.
• PNG files are raster files as are JPG’s (.jpeg) files, so they behave like photos.
• Our PNG’s are 32bit files.
• You can insert or paste PNG’s directly into MS Word 365 or PowerPoint 365.
• You can view PNG files by dragging them into a browser tab.
• You can edit PNG files using programs such as Adobe Photoshop.