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5.6 Light and colour stimuli

Visible light is created when the electric structure of the atom in a  photon is discharged. That's how the electromagnetic radiation is released and we perceive it as light. Light can move in a vacuum and doesn't need any transmitter substance. (The speed of light is a bit less  than 300,000,000 m per second.) Light has both particle-like and wave-like nature and moves in  transverse electromagnetic waves in a rectilinear direction in the same substance. Light rays bend when they pass through a surface between one transparent material and another. This change of direction (refraction) can be seen when the Sun is low, and blue colour is refracted and light rays seem to come from every direction. After this blue moment the reddish shades of sunset are left in the  sunlight because sunbeams travel the longest way through the atmosphere. At dawn the same phenomena are repeated but in the reverse order. (Peda net>Ylöjärvi / Valo ja väri. Light and colour.)

The primary properties of light waves are intensity (amplitude), colour (wavelength) and polarization (frequency). Visible light is the part of the electromagnetic spectrum that the human eye is able to perceive. Its wavelength is 400 - 780 nm (nanometres) and its frequency is about 750 - 380 THz (terahertz) . The wavelength of light determines the colour which is perceived. The wavelengths of colours are about the following: violet: 380 - 450 nm, blue: 450 - 490 nm, green: 490 - 560 nm, yellow: 560 - 590 nm, orange: 590 - 630 nm and red: 630 - 760 nm. In the visible sunlight there are all the colours of a rainbow which together make white colour.(Wikipedia. Light / Electromagnetic and visible light.)

At the blue end of the spectrum the wavelength of radiation is shorter and it contains more energy. The amount of high-energy bluish light is about a third of visible light and its frequency 380 - 500 nm. The wavelength of ultraviolet radiation (light) is shorter than that of the light visible to the human eye. At the red end of the spectrum there is infrared radiation whose wavelength is longer. It's thermal radiation which becomes visible (red) at a high temperature of about 500° and at higher temperatures it gets white.  The human eye is best able to see yellow or yellowish green light, whose wavelength is 555 nm. ( Finnish  Meteorological Institute. Light and spectrum, Electromagnetic radiation.)

Surfaces of different type and colour reflect light in a different way. Light goes to the retina at the back of the eye where radiation turns into nervous impulses. They transmit the information to the brains where the visual perception is created. Cone cells on the retina which are sensitive to light sense only intensive light, being the most sensitive at a wavelength of 555 nm. They are able to sense colours and they are concentrated around the point of sharp vision.

Rod cells only sense light and they can function in the dark, too. They outnumber cone cells and are found in a larger area than cone cells. That's why colours can't be seen either in dim light or on the fringe of the visual field. Because  there are no rod cells on the point of sharp vision you can't see too carefully in dim light / at dusk.

On the retina there are also cells that can't see, but they influence our alertness and tiredness by regulating the secretion of melatonin. These cells are sensitive to short wavelengths, i.e. the colours of the blue end (of spectrum).

The cone cells on the retina in the eye sense wavelengths which are caused by different colours. The interaction of the cone cells which sense the colours red, green and blue create the perception of colour. Near the point of sharp vision there are a lot of cells that especially sense red and green. The cone cells sensing blue colour are located in a wider area on the retina. If some wavelength of the spectrum is missing from the light it cannot be reflected from the surface that is being lit and the eye cannot sense the colour as a natural colour. (Ensto/Light/The function of the eye).

As for the function of the human eye and body, incandescent light (thermal light) from the Sun and other stars, from flames of fire or incandescent lamps are the best because of their natural quality: the whole electromagnetic spectrum of visible light. High-energetic, short-waved blue light is used in many artificial sources of light and electric devices with screens.. When you predispose to it more than in the natural visible light you would, the sense of balance reacts because it stimulates the body too much,  causing e.g. sleep disorders.

Infrared at the red end of the spectrum is  used to create pleasant sensations in the body. However, the overall electromagnetic effect on the body may be something else because it's thermal radiation which is directed through the skin into the tissue under it. Again, it's the sense of balance that is prepared to eliminate any strange electromagnetic intruders by stimulating vital functions in the body. This is may be a risky thing for a body that is strained by the DSB.

To perceive light and colour requires transportation of electric impulses in the neural pathwaysbetween the eyes and the brains. When the light / lighting has the properties of natural visible light it functions best in the body. Again, any deviations from the natural electromagnetic spectrum aredetected by the sense of balance which follows the function of the eyes very carefully since they are close partners in keeping the body balanced in relation to the gravity.

It goes both ways: disturbing light and colour stimuli irritate the sense of balance, which in turn, often tenses the small muscles in the eyes first and adrenaline makes the senses oversensitive. This vicious circle can disturb anything the eyes are supposed to do. This is likely to result in the nastier consequences the more the sense of balance is affected by the DSB.

The following chapter 5.7 The sense of balance and the immunity of the human body

 See 4.1.1 Muscles in the eye

         18 Is anything else needed? / Spectacles.

         Theme page 22. The DSB, the TSB and seeing, reading, writing and learning