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 colours.
- 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 a colour space 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.
A rainbow is an optical effect produced by illuminated droplets of water. Rainbows are caused by reflection, refraction and dispersion of light in individual droplets and result in the appearance of an arc of spectral colours.
A primary rainbow is formed when sunlight is refracted and reflected by water droplets in the air. The colours of a primary rainbow are always in the same order, with red on the outside and violet on the inside.
- A primary rainbow appears when sunlight is refracted as it enters raindrops, reflects once off the opposite interior surface, is refracted again as it escapes back into the air, and then travels towards an observer.
- The colours in a primary rainbow are always arranged with red on the outside of the bow and violet on the inside.
- The outside (red) edge of a primary rainbow forms an angle of approx. 42.40 from its centre, as seen from the point of view of the observer. The inside (violet) edge forms at an angle of approx. 40.70.
- To get a sense of where the centre of a rainbow might be, imagine extending the curve of a rainbow to form a circle.
- If your shadow is visible as you look at a rainbow its centre is aligned with your head.
- A primary rainbow is only visible when the altitude of the sun is less than 42.4°.
- Primary bows appear much brighter than secondary bows and so are easier to see.
- The curtain of rain on which sunlight falls is not always large enough or in the right place to produce both primary and secondary bows.
The most common atmospheric rainbow is a primary bow.
- Primary rainbows appear when sunlight is refracted as it enters raindrops, reflects once off the opposite interior surface, is refracted again as it escapes back into the air, and then travels towards an observer.
- The colours in a primary rainbow are always arranged with red on the outside of the bow and violet on the inside.
- The outside (red) edge of a primary rainbow forms an angle of approx. 42.40 from its centre, as seen from the point of view of the observer. The inside (violet) edge forms at an angle of approx. 40.70.
- To get a sense of where the centre of a rainbow might be, imagine extending the curve of a rainbow to form a circle.
- If your shadow is visible as you look at a rainbow its centre is aligned with your head.
- A primary rainbow is only visible when the altitude of the sun is less than 42.4°.
- Primary bows appear much brighter than secondary bows and so are easier to see.
- The curtain of rain on which sunlight falls is not always large enough or in the right place to produce both primary and secondary bows.
Primary visual cortex
The visual cortex of the brain is part of the cerebral cortex and processes visual information. It is in the occipital lobe at the back of the head.
Visual information coming from the eyes goes through the lateral geniculate nucleus within the thalamus and then continues towards the point where it enters the brain. The point where the visual cortex receives sensory inputs is also the point where there is a vast expansion in the number of neurons.
Both cerebral hemispheres contain a visual cortex. The visual cortex in the left hemisphere receives signals from the right visual field, and the visual cortex in the right hemisphere receives signals from the left visual field.
[Cerebral hemispheres, occipital lobes, primary visual cortex, optical radiations]
The visual cortex of the brain is part of the cerebral cortex and processes visual information. It is in the occipital lobe at the back of the head.
- Visual information from the eyes goes through the lateral geniculate nucleus within the thalamus and then continues towards the point where it enters the brain. At the point where the visual cortex receives sensory inputs is also a point where there is a vast expansion of the number of neurons
- Both cerebral hemispheres contain a visual cortex. The visual cortex in the left hemisphere receives signals from the right visual field, and the visual cortex in the right hemisphere receives signals from the left visual field.
In the field of optics, a prism is an object made of glass or other transparent material with flat, polished surfaces.
- Prisms are often used for experimental purposes to study the refraction and dispersion of light.
- They are popularly known to split light into rainbow colours.
- A triangular prism consists of two triangular ends and three rectangular faces.
- If white light is to be refracted or dispersed by a prism into its component colours a narrow beam is pointed towards one of the rectangular faces.
- Dispersive prisms are used to break up light into its constituent spectral colours.
- Reflective prisms are used to reflect light, to flip or invert a light beam.
- Triangular reflective prisms are a common component of cameras, binoculars and microscopes.
Wave propagation refers to any of the ways in which waves travel.
- Electromagnetic radiation propagates through space, carrying electromagnetic energy in the form of electromagnetic waves.
- The propagation of electromagnetic radiation through space is sometimes described in terms of photons rather than waves.
- Photons are particles that are sometimes used to explain the behaviour of electromagnetic waves.
- Propagation of electromagnetic waves can occur in a vacuum as well as through different media. Other wave types such as sound waves cannot propagate through a vacuum and require a transmission medium.
- All forms of electromagnetic radiation propagate in similar ways whether they are radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, or gamma rays.
Wave propagation is any of the ways in which waves pass through a vacuum or medium.
- Electromagnetic radiation propagates through space, carrying electromagnetic energy in the form of electromagnetic waves.
- The propagation of electromagnetic radiation through space is sometimes described in terms of photons rather than waves.
- Photons are particles that are sometimes used to explain the behaviour of electromagnetic waves.
- Propagation of electromagnetic waves can occur in a vacuum as well as through different media. Other wave types such as sound waves cannot propagate through a vacuum and require a transmission medium.
- All forms of electromagnetic radiation propagate in similar ways whether they are radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays or gamma rays.
About pure & vivid colours
Pure colours
A pure colour is a single unique spectral colour and so a fully saturated colour produced by a single wavelength of light.
- In the context of colour, purity and saturation refer to the intensity of a hue.
- Unsaturated colours on the other hand can appear to be:
- Misty or milky the nearer they are to white.
- Dull and washed out as their hue disappears, leaving achromatic grey tones.
Vivid colours
The vividness of a colour refers to its brightness.
- When a colour is at its most vivid then it is at maximum brightness (100%).
- As colours lose their brightness they appear progressively darker in tone until at minimum brightness they appear black (0%).
A pure colour is a monochromatic colour with no added tint or shade and can be produced by a single wavelength of light at full saturation.
- Any single wavelength of light at full saturation and brightness is perceived as a pure colour.
- Saturation refers to the purity or vividness of a colour, while brightness refers to the intensity or amount of light in a colour.
- Tint refers to a hue that has been mixed with white, while shade refers to a hue that has been mixed with black.
- A monochromatic colour on the other hand refers to a colour produced by a single wavelength of light but including all of its tints and shades.
- Colours produced by a narrow band of adjacent wavelengths may appear to be pure colours.
- Spectral colours are the hues that are produced by the separation of white light into its component colours by refraction or diffraction, as seen in a rainbow.
Qualitative refers to a description or analysis of something based on its qualities or attributes, rather than on measurable or quantitative data.
- Qualitative analysis in physics focuses on the inherent properties or characteristics of the thing being studied, rather than on numerical values or precise measurements.
- Qualitative analysis involves making observations, interpreting patterns and relationships, and drawing conclusions based on these observations, rather than relying solely on numerical data or statistical analysis.
- Qualitative analysis might involve making observations and drawing inferences about the behaviour of a system or object based on its properties, such as its shape, colour, texture, or motion.
