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the value of light
A human being needs daylight for an optimal performance and that fact largely defines the application area of artificial sources of light: Bringing light to places and in periods where nature cannot

bring it in order to increase our live- and work space. The application area of artificial sunlight is comprehensive. From lighting to create a daylight situation in which we can work, travel or relax to lighting that allows for complicated internal surgery or, subject of this site, light that is supposed to have a specific positive influence on our health.

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extralight/sunshine/ light

the colours of the sun
The colour of bright sunlight seems to be yellow/white but that is somewhat an illusion. In fact white light consists of a combination of rays with different wavelengths in the visible part of the spectrum. In 1665 it was Isaac Newton who noticed that images he made with his self fabricated lenses became vague at the edges and were surrounded with a small area of light in different coloured bands. After a long period of experimenting he finally concluded that the phenomenon was not caused by imperfections in the lenses itself but that the

cause was to be found in refraction of the light. This refraction

such a bundle of light will be refracted in separate colours. In sunlight all colours of the spectrum are present but due to a partial absorption of some colours by the atmosphere a rainbow seems to have seven distinguished bands in the colours red, orange, yellow, green, blue, indigo and violet with a more or less gradually transition from one colour to another (see electromagnetic spectrum). Principally the combination of an equal amount of all colours would result in a

pure white light but in relation to sunlight the situation is a little

more complicated since the presence of the colours green and yellow is relatively high. Besides that the human eye is relatively sensitive for the colour yellow but whether or not this is caused by the composition of the sunlight is not completely clear. The final result however is that we mostly notice the sunlight with a touch of yellow. When the sun is

the colours of the rainbow
In research centres its is often a prism that is used to refract light. A prism is a triangular piece of glass that, due to its specific shape, is capable to refract light into its separate components. In a prism the unexpected side effect of Isaac Newton his lenses is optimised and revalued into wanted behaviour. The best known natural example of colour separation through refraction is the rainbow. Individual drops of water in a rain shower, in a fountain or a in

curtain of water from a garden hose act as small prisms that partially let pass the light and partially refract it. The angle of refraction depends on the wavelengths of the different colour

components of the incoming light, an effect that we observe as a rainbow.

occurs when a bundle of light passes two substances with different propagation characteristics, for instance air and water or air and glass. In air the propagation speed of light is higher than it is in water or in glass. This causes the light to bend more ore less, depending on the angle at which the light falls unto the water or glass. Since the degree of bending is

slightly different for the several colour components of white light,

located near the horizon, the atmosphere will cause an additional filtering of the sunlight making its colour seem to be more reddish.

the nature of light
The phenomenon of light has not been understood for thousands of years. In 1672 Isaac Newton revealed his hypothesis about the

behaviour of light in which he stated that light consisted of small particles. This theory was contradictory to that of Christiaan Huygens who, in 1678, revealed his undulation theory in which he stated that the behaviour of light was comparable with that of a wave. In the end it turned out that both were partly right. In contrast with sound, which propagates as a pure wave, light (and any other form of electromagnetic radiation) behaves not only as a wave but

also as radiation. A balanced explanation that included both properties emerged no earlier than the twentieth century with the development of quantum mechanics.