Introduction

Electromagnetic radiation is characterized through its wavelength (or frequency) and its intensity. When the wavelength is within the visible spectrum (the range of wavelengths creatures can recognize, approximately from 380 nm to 740 nm), it is identified as 'visible light'. Most light sources produce light at many different wavelengths; a source's spectrum is a distribution giving to its intensity at each wavelength. Even though the spectrum of light obtained via the eye from a given direction verifies the colour sensation in that direction, there are many more possible spectral amalgamations than colour sensations. Consequently, one might formally define a colour as a class of spectra that provides increase to the similar colour sensation, although these classes would fluctuate extensively among different species, and to a lesser extent among individuals within the similar species. In each these class, the members are termed metamers of the colour in question.

Definition of Colour

Colour is merely described as the light of different wavelengths and frequencies. Light, though, is just one shape of energy that we can really see that is made up of photons.

History of Colour

Several  of  the  early  studies  and  theories  about  light  were  done  via Aristotle. He determined, which through blending 2 colours, the 3^rd is generated. He did this through a yellow and blue piece of glass that when brought mutually generated green. He as well discovered that light travels in waves. Plato and Pythagoras as well studied light. In the 10^th century, Al- Haytham examined into colour and his discovering inspired Newton. During the middle Ages, Paracelsus reintroduced the acquaintance and philosophy of colour using the power of the colour rays for healing along through music and herbs. Unluckily, he was hounded all through Europe and ridiculed for his work. Most of his manuscripts were burnt, but now he is thought of, via many, to be one of the greatest doctors and healers of his time. A man, it would seem, very much ahead of his time. Not only do we now utilize Colour Therapy once again, but, his other ideas, using herbs and music in healing, can as well be seen reflected in many of the complementary therapies now fairly in ordinary place.

A pioneer in the field of colour, Isaac Newton, in the year 1672 published his 1^st,  controversial  paper  on  colour,  and  forty  years  later,  his  work 'Opticks'. Newton passed a beam of sunlight through a prism, when the light came out of the prism it was not white but was of 7 different colours: Red, Orange, Yellow, Green, Blue, Indigo and Violet. The spreading into rays of these colours was termed 'dispersion' via Newton and he termed the different coloured rays the 'spectrum'. He determined that when the light rays were passed once more throughout a prism, the rays turned back into white light. If one ray was passed throughout the prism it would approach out the alike colour as it went in. Newton concluded, which white light was made up of seven different coloured rays.

Where Does Colour Come from

Colour comes from light. We can see seven main colours of the Visible Spectrum. The retinas in our eyes though have 3 kinds of colour receptors in the shape of cones, we can really only detect 3 of such visible colours - red, blue and green. Such colours are termed additive primaries. It is such 3 colours that are blended in our brain to create all of the other colours we see. The wavelength and frequency of light as well influences the colour we see. The 7 colours of the spectrum all have fluctuating wavelengths and frequencies. Red is at the lower finish of the spectrum and has an elevated wavelength but lower frequency than that of violet at the top finish of the spectrum, which has a lower wavelength and higher frequency.

To physically see this, we require a prism. When light from the sun passes through a prism, the light is split into the 7 visible colours through refraction. Refraction is caused through the change in speed experienced via a wave of light when it changes medium.

Fig: Colours of Visible Spectrum

Electromagnetic Waves and Visible Spectrum

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The electromagnetic spectrum of an object is the trait distribution of electromagnetic radiation released or absorbed through that particular object.

The electromagnetic spectrum expands from below frequencies utilized for modern radio through to gamma radiation at the short wavelength end, covering wavelengths from thousands of kilometers downward to a fraction of the size of an atom.

The long wavelength limit is the size of the cosmos itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length, even though in principle the spectrum is infinite and continuous.

Usually, electromagnetic radiation (EM) is classified through wavelength into radio wave, microwave, infrared, the visible region we perceive as light, ultraviolet, X-rays and gamma   rays. The behaviour of EM radiation based on its wavelength. When EM radiation relates by single atoms and molecules, its behavior as well based on the amount of energy per quantum (photon) it carries.

The diagram below illustrates what small part of the whole electromagnetic visible spectrum light actually forms.

Fig: Nature of Electromagnetic Radiation

The amount of energy in a given light wave is proportionally related to its frequency; therefore a elevated frequency light wave has a elevated energy than that of a low frequency light wave.

E= hν where E= Energy; h=Planck' constant; v= velocity of light

Wavelengths and Frequencies of Colour

Each colour has its own particular wavelength and frequency. Each colour can be calculated in units of cycles or waves per second. If we can visualize light traveling in waves like that in an ocean, it is such waves that have the properties of wavelength and frequency. A wavelength is the distance between the similar locations on adjacent waves.

Each of such waves has a dissimilar wavelength and speed of vibration. Mutually they form the electromagnetic spectrum.  Light travels in waves.

The frequency of a wave is computed through the no of complete waves or wavelengths that pass a given point each second. Every one light travels at the similar speed but each colour has a dissimilar wavelength and frequency. It is such different wavelengths and frequencies that reason different colours of light to be divide and visible whenever passing through a prism. This can be evaluated to the radio waves that have different frequencies and wavelengths in which certain stations can only be listened to at a particular frequency or wavelength. So, colour blue, for instance, - can only be observable at a particular frequency and wavelength range. The elevated the frequency of a colour, the closer the waves of its energy.

Higher frequency colours are violet, indigo, and blue while the lower frequency colours are yellow, orange and red. A high frequency light wave has a higher energy than that of a low frequency light wave.

Properties of Colour

Each colour has its own properties through its own wavelength and frequency. Although white could be said to be a colour, it is usually not comprised in the scientific spectrum as it is in fact made up of all the colours of the spectrum, but it is often being termed to as a colour.

Table: Colour and Relative Property

Colour perception

We see colour throughout the sensors in the retina of the eye termed rods and cones. The rods are sensitive to low light and the cones that need a greater intensity of light, are sensitive to colour. The message is exceeded to the optic nerve and then on to the brain.

Fig: Colours and Eyes

The eye picks up colour and light through the rods and cones. It is the Cones, which detect colour. Each cone encloses one of 3 pigments sensitive to either red green or blue. There are about 120 million rods and about 6 to 7 million cones in the human eye. Rods are more sensitive than the cones but they aren't sensitive to colour, they perceive pictures as black, white and dissimilar shades of grey. More than one thousand times as susceptible, the rods respond enhanced to blue but extremely little to red light.

Each pigment absorbs a meticulous wavelength of colour. There are short wavelength cones that suck up blue light, middle wavelength cones, which absorb green light, and long wavelength cones that absorb red light. Whenever we examine a colour that has a wavelength between that of the primary colours red, green and blue, mixtures of the cones are stimulated. An instance could be that yellow light excites cones that are sensitive to red and green light. The consequence is that we can detect light of all colours in the visible spectrum.

People who suffer from colour blindness have less numeral of meticulous cones than normal, so they get confused through colours. If we lose our eye sight, the body adapts and obtains colour rays throughout the skin. It receives time for the body to adapt, but it has been exposed that people, who are blind, can discriminate between different colours.

Objects colour

Everything we can observe has a colour. Around us, in our homes, at work, in nature, in space - it is worldwide; everywhere has a colour, of several sorts. The colour of anything we examine depends upon a few factors. Initially - Everything is made up of electrons and atoms. Different substances, objects and items have a dissimilar make up of atoms and electrons. Any object, through its nature, will, when exposed to light, do one of the subsequent: reflect or scatter light (reflection and scattering), absorb light (absorption), do nothing (transmission) and refract light (refraction).

Reflection and Scattering

Numerous objects reflect light to several degrees, but something that is chiefly reflective, has more free electrons that are able to pass from one atom to another through ease. The light energy that is engrossed through such electrons isn't passed onto any other atoms, in its place, the electrons vibrate and the light energy is sent out of the substance at the similar frequency as the original light coming in. Smooth surface reflect light while rough surface scatter it and the angle of incidence is always equal to angle of reflection.

Absorption

When something illustrates to have no reflection or is opaque, then the incoming light source frequency is alike as or extremely closes to the vibration frequency of the electrons in the following material. The electrons of the substance absorb the energy of the light source, and since the light is absorbed, the material or object appears opaque - it has extremely little or no reflection.

Transmission

This takes place when the energy of the incoming light is either much lower or much higher than the energy or frequency needed to make the electrons in the particular material vibrate. As a consequence of this, the electrons in an object that shows to be transparent, in its place of capturing the light energy, allows the light wave pass through the object material unchanged, therefore the object substance is transparent to that frequency of light.

Refraction

If we have ever put a straw in a drink, then we might have observed that the straw shows to be bent under the water. The reason for this is Refraction.  If  the  energy of  the  incoming  light  is  the  same  as  the vibration frequency of the electrons in the substance, the light is able to go deep into the substance and causes small vibrations in the electrons.

Such vibrations are passed on to the atoms via the electrons, and in revolve they send out light waves at the same frequency as the incoming light. Although this happens extremely quickly, some of the light that is inside of the material slows down, but the frequency of the light outside the material remains the similar. The consequence of this is that the light inside the substance is bent. The angle of the distortion (refraction) depends upon how much the material is able to slow down the light, in this case as in the image above water.

A good instance as to why objects possess a particular colour is exposed in the picture below (of ripe tomatoes). Tomatoes appear to be red since when ripe, tomatoes enclose a carotenoid recognized as 'Lycopene'. Lycopene is a bright red carotenoid pigment, a phytochemical found not only in tomatoes but as well other red fruits. Lycopene absorbs most of the visible light spectrum, and being red in colour, Lycopene reflects largely red back to the viewer, and therefore, a ripe tomato shows to be red.

Another instance is the green leaf or green grass that utilizes Chlorophyll to transform light into energy. Since of its environment and chemical makeup, Chlorophyll  absorbs  the  blue  and  red  colours  of  the  spectrum  and reflects the green. The green is reflected back out to the viewer making the grass and leaves appear green.

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