What are colours and how do people understand them?

Sub: Science and tech

Sec: Msc

What is colour?

Colour is a type of information our eyes receive and process based on electromagnetic radiation.
An object by itself can’t be said to have a color but based on which frequencies of visible-light radiation it absorbs, reflects, and/or scatters, we can perceive the object to have a particular color.

How are humans able to perceive colors?

In the human eye, the rod and the cone cells receive information in the light that strikes the eye.
The rod cells record brightness while the cone cells record the wavelengths, which the human brain interprets as color.
Human beings have three types of cone cells.
Each type is sensitive to light of a different wavelength, and they work together to input color information to the brain.
The possession of three types of cone cells is why humans are called trichromats.
Many birds and reptiles, on the other hand, are tetrachromats (four types of cone cells).
While human vision is restricted to wavelengths from 400 nm to 700 nm (visible light), honeybees can also ‘see’ ultraviolet light and mosquitoes and some beetles can access information in some wavelengths of infrared radiation

Science of colors:

Until the late 19th century, traditional color theory specified the different ways in which dyes, pigments, and inks could be mixed to make other colors.
In this paradigm, there were three primary colors e.g. red, yellow, and blue.
These colors when combined in different ways could produce all the colors the human eye is capable of seeing.
Modern color theory, more accurately color science, rejected the idea of there being three fixed colors. According to color science, all the colors that could be produced by combining any three colors in different ways is called the gamut of those three colors.
Each color in a gamut populates a given color space, and all color spaces are smaller than the full range of colors the eye can see.

Rendering of colors:

There are two broad ways to render colors i.e. additive and subtractive coloring.
In additive coloring, light of different wavelengths is ‘mixed’ to yield light of one combined color.
A common color space associated with additive coloring is the RGB space: where red, green, and blue when added to each other in varying measures produces other colors.
In subtractive coloring, a color is rendered by passing white light through a medium that absorbs, or takes away, specific wavelengths of light thereby leaving the rest to render a particular color.
The typical examples include dyes, pigments, and inks. A dye is a chemical compound that can absorb certain wavelengths of light.
When a cloth is dyed, the dying compound forms chemical bonds with compounds in the cloth and imbues the cloth with the corresponding color.

What are the properties of color?

In color science, all colors however rendered are said to have a few appearance parameters: hue, brightness, lightness, and chromaticity.
Hue:
- A Technical committee of the International Commission on Illumination specified the definition of hue to be the degree to which a given (perceived) color can be said to be “similar to or different from” perceived “red, orange, yellow, green, blue, violet”.
- Isaac Newton defined complementary colors on the basis of hue i.e. if two colors combine to produce a grayscale color i.e. lacking in hue — they are complementary.
Brightness:
- Brightness is related to an object’s luminance.
- The luminance is the power emitted by a source of light per unit area, weighted by wavelength.
- The eye’s subjective perception of this power in some direction is inferred as the source’s brightness.
Lightness:
- Lightness refers to the extent to which a coloured object appears light compared to a white-coloured object that is well lit.
Chromaticity:
- The chromaticity, or chromatic intensity, has to do with the human perception of color and depends on the color’s quality irrespective how well it is lit.

What are LEDs?

A light-emitting diode (LED) is a semiconductor device that emits light when an electric current is passed through it.
Light is produced when the particles that carry the current (known as electrons and holes) combine together within the semiconductor material.

What are Blue LEDs?

Blue LED Light can be defined as light given off from light-emitting diodes (LEDs) in the visible light spectrum between the wavelengths of 400 to 500 nanometers (nm).
Blue Light sits on the spectrum between violet and green.
Blue LEDs have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers.
By varying the relative In/Ga fraction in the InGaN quantum wells, the light emission can in theory be varied from violet to amber.