Continuous Colour from Red to Violet
- Electromagnetic waves, which are a form of electromagnetic radiation, propagating from a light source, travel through space and encounter different materials.
- Colour is not a property of electromagnetic radiation, but an aspect of visual perception.
- A human observer can distinguish between colours corresponding with many thousands of wavelengths of light in the visible spectrum. These colours are often called spectral colours.
- The largest part of the electromagnetic spectrum is outside the wavelengths of visible light and so invisible to a human observer.
- Beyond red are infrared, microwaves and radio waves for example. Some radio waves have a wavelength longer than a kilometre (1000 metres).
- Beyond violet are ultraviolet, X-rays, and gamma rays for example. Some gamma rays have a wavelength of one billionth part of a metre.
- There are no properties of electromagnetic radiation that distinguish visible light from other parts of the electromagnetic spectrum.
- Objects appear to be different colours to an observer depending on the wavelengths, frequencies and amplitude of visible light at the moment it strikes the retina at the back of the eye.
Continuous Colour from Red to Violet
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About the diagram
About the diagram
- This diagram is about the visible spectrum and which wavelengths of electromagnetic radiation correspond with the different colours we see in the world.
- It shows that a human observer can distinguish between colours corresponding with thousands of wavelengths of visible light.
- The visible spectrum (a rainbow for example) can be thought of as six bands of colour or as being made up of light rays of different wavelengths, each distinguished by its measurement in nanometres.
- The visible spectrum is made up of an infinite gradation of wavelengths and colours. The total number of colours in the world is limited only by the sensitivity of human vision and the size of the units of measurement used to calculate wavelength.
- The list down the left of the diagram represents the visible spectrum as bands of wavelengths and bands of colour.
- The scale along the bottom marks out the visible spectrum in nanometres with the corresponding colours shown above.
- 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.
Some key terms
The electromagnetic spectrum includes electromagnetic waves with all possible wavelengths of electromagnetic radiation, ranging from low energy radio waves through visible light to high energy gamma rays.
- There are no precisely defined boundaries between the bands of electromagnetic radiation in the electromagnetic spectrum.
- The electromagnetic spectrum includes, in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
- Visible light is only a very small part of the electromagnetic spectrum.
- The wavelength of an electromagnetic wave is measured in metres.
- Each type of electromagnetic radiation, such as radio waves, visible light and gamma waves, forms a band of wavelengths on the electromagnetic spectrum.
- The visible part of the electromagnetic spectrum is composed of the range of wavelengths that correspond with all the different colours we see in the world.
- Human beings don’t see wavelengths of visible light, but they do see the spectral colours that correspond with each wavelength and the other colours produced when different wavelengths are combined.
- The wavelength of visible light is measured in nanometres. There are 1,000,000,000 nanometres to a metre.
- 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.
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