# Combining Red Green & Blue Light

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This diagram explains what happens when red, green and blue primary colours are projected onto a dark surface so that they overlap.

What you need to remember:

• Mixing different wavelengths of light to produce other colours, is called an additive colour model or an additive approach to colour.
• Red, green and blue (RGB) are additive primary colours. This means that when these wavelengths of light are projected onto a dark surface they combined to produce other colours.
• If wavelengths of light corresponding with all three additive primary colours are projected in equal amounts onto a dark surface the result is white.
• If wavelengths of light corresponding with all three additive primary colours are projected in unequal amounts onto a dark surface many thousands of colours can be produced.
• Secondary colours are the colours produced when pairs of primary colours are combined in equal or unequal proportions.

Understanding the diagram:

• Three circles of light are projected onto a dark surface. These are the additive primary colours – red, green and blue.
• Where the primary colours overlap they produce the secondary colours – yellow, magenta and cyan.
• Where all three primary colours overlap they produce white.
• The bottom of the diagram shows which primary colours are mixed in pairs to produce each secondary colour.
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## Description

#### Combining Red, Green & Blue Light

###### TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
Blue and red are the two primary RGB colours that together make magenta!
Secondary colours are the colours produced by mixing pairs of primary colours in equal proportions. The secondary colours in the RGB colour model are cyan, magenta and yellow.
Additive primary colours are three wavelengths of light that produce white when combined together in equal proportions.
When wavelengths corresponding with red, green and blue are projected onto a neutral coloured surface they produce white.

• This diagram explains what happens when red, green and blue primary colours are projected onto a dark surface so that they overlap.
###### What you need to remember
• Mixing different wavelengths of light to produce other colours, is called an additive colour model or an additive approach to colour.
• Red, green and blue (RGB) are additive primary colours. This means that when these wavelengths of light are projected onto a dark surface they combined to produce other colours.
• If wavelengths of light corresponding with all three additive primary colours are projected in equal amounts onto a dark surface the result is white.
• If wavelengths of light corresponding with all three additive primary colours are projected in unequal amounts onto a dark surface many thousands of colours can be produced.
• Secondary colours are the colours produced when pairs of primary colours are combined in equal or unequal proportions.
###### Understanding the diagram
• Three circles of light are projected onto a dark surface. These are the additive primary colours – red, green and blue.
• Where the primary colours overlap they produce the secondary colours – yellow, magenta and cyan.
• Where all three primary colours overlap they produce white.
• The bottom of the diagram shows which primary colours are mixed in pairs to produce each secondary colour.
###### Spectral and RGB colours
• Spectral colour should not be confused with RGB colour.
• Spectral colours are components of the visible spectrum.
• RGB colours are produced by mixing wavelengths of light corresponding with the three additive primary colours, red, green and blue.
• A diagram of spectral colour is usually presented in the form of a continuous linear spectrum organised by wavelength, so with red at one end and violet at the other.
• A diagram of RGB colour is often represented in the form of a colour wheel and shows the colours produced by mixing adjacent colours on the wheel.

#### Some key terms

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.

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.

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

• A rainbow spans the continuous range of spectral colours that make up the visible spectrum.
• The human eye is tuned to the visible spectrum and so to spectral colours between red and violet.
• ROYGBV are colours associated with a range of wavelengths rather than with unique values.
• The visible spectrum is the small band of wavelengths within the electromagnetic spectrum that corresponds with all the different colours we see in the world.
• The fact that we see the distinct bands of colour in a rainbow is an artefact of human colour vision.
• To be clear about the RGB colour model it is useful to remember first that:
• The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
• A spectral colour is a colour corresponding with a single wavelength of visible light, or with a narrow band of adjacent wavelengths.
• The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. However, because of the way the eye works, we can see many other colours which are produced by mixing colours from different areas of the spectrum. A particularly useful range of colours is produced by mixing red, green and blue light.
• RGB colour is an entirely different approach to producing and managing colour.
• RGB colour is an additive colour model in which red, green and blue light is combined in various proportions to reproduce a wide range of other colours. The name of the model comes from the initials of the three additive primary colours, red, green, and blue.
• Except for the three primary colours, RGB colours are not spectral colours because they are produced by combining colours from different areas of the visible spectrum.
• RGB colour provides the basis for a wide range of technologies used to reproduce digital colour.
• RGB colour provides the basis for reproducing colour in ways that are well aligned with human perception.
• When an observer has separate controls allowing them to adjust the intensity of overlapping red, green and blue coloured lights they are able to create a match for a very extensive range of colours.
• When looking at any modern display device such as a computer screen, mobile phone or projector we are looking at RGB colour.
• Magenta is an RGB colour for which there is no equivalent spectral colour.

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.

Primary colours are a set of colours from which others can be produced by mixing (pigments, dyes etc.) or overlapping (coloured lights).

• 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 the electromagnetic spectrum that results in the perception of colour.
• A set of primary colours is a set of pigmented media or coloured lights that can be combined in varying amounts to produce a wide range of colour.
• This process of combining colours to produce other colours is used in applications intended to cause a human observer to experience a particular range of colours when represented by electronic displays and colour printing.
• Additive and subtractive models have been developed that predict how wavelengths of visible light, pigments and media interact.
• RGB colour is a technology used to reproduce colour in ways that match human perception.
• The primary colours used in colour-spaces such as CIELAB, NCS, Adobe RGB (1998) and sRGB are the result of an extensive investigation of the relationship between visible light and human colour vision.