1.1 light source and light interaction


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1.1 light source and light interaction

  1. 1. Light, light sourcesand light interactions HISTORY - INTRODUCTION compiled by TANVEER AHMED 1
  2. 2. Table of contents1. Three factors2. Introduction3. Direct emission4. The dye and pigment technologist may use light:5. The Electromagnetic spectrum6. Newton’s Prismatic Hues7. Electromagnetic radiation discovery by the astronomer Herschel (IR)8. German physicist J W Ritter,UV9. Scottish physicist and mathematician James Clerk Maxwell In 186010. German physicist Heinrich Hertz-1887 RADIO WAVES compiled by TANVEER AHMED 2
  3. 3. Three factors • Colour in a manufactured object is normally obtained by applying • a colorant (dye or pigment) • to a polymer substrate, • such as textile, paper or paint medium. • The appearance of such surface colours depends on three factors compiled by TANVEER AHMED 3
  4. 4. Three factors 1. the nature of the prevailing illumination under which the coloured surface is viewed 2. the interaction of the illuminating radiation with the coloured species in the surface layers, particularly within the visible region of the electromagnetic spectrum 3. the ability of the radiation that is transmitted, reflected and scattered from the coloured surface to induce the sensation of colour in the human eye/brain system. compiled by TANVEER AHMED 4
  5. 5. compiled by TANVEER AHMED 5
  6. 6. INTRODUCTION • Physically, for example, • The production of colour • by a dyed or pigmented surface is most simply explained in terms of the process of selective absorption of • certain wavelength portions of the incident white light coupled with – transmission, – reflection – and scattering of the non-absorbed radiation compiled by TANVEER AHMED 6
  7. 7. INTRODUCTION • Colour can also be produced, however, by other types of light interaction: – by interference and by diffraction, • for example. The process of light interference produces coloured effects in – peacocks’ feathers – and the wing-cases (elytra) of beetles, • And Light diffraction is increasingly being used to produce interesting forms of coloured materialssuch as • liquid crystal displays (LCD) • and polarisation colours. compiled by TANVEER AHMED 7
  8. 8. Direct emission • Many modern light sources such as lasers, coloured light tubes • (such as sodium vapour street lamps) • and video or television screens • emit coloured radiation directly, rather than producing the colour by selective absorption. compiled by TANVEER AHMED 8
  9. 9. Direct emission(deactivation) • Lasers and sodium vapour lamps produce their coloured radiation by – electronic excitation – and deactivation processes, • the latter resulting in direct emission of radiation in appropriate narrow wavebands within the visible spectrum, • giving rise to a particular hue which is characteristic of the wavelengths or combinations of wavelengths in the emitted radiation. compiled by TANVEER AHMED 9
  10. 10. The dye and pigment technologist may use light: (a) to illuminate a coloured surface for purposes of assessing colour appearance (b) to irradiate a coloured surface to assess its light stability (c) in optical and spectroscopic instruments, to assess optical properties of a surface or to undertake chemical and other scientific studies of the colorants used. compiled by TANVEER AHMED 10
  11. 11. THE ELECTROMAGNETI C SPECTRUMVisible light is a form of electromagnetic radiation,distinguished from other forms byits ability to be detected in the retina of the human eye. compiled by TANVEER AHMED 11
  12. 12. Newton’s Prismatic Hues • The first real progress in understanding • the relationship between light and colour came in 1672, with the publication of Newton’s descriptions and explanations of the effect of passing white light from • the sun through combinations of prisms. • In describing his experiments, carried out • in 1666, Newton used the word ‘spectrum’ to describe the range of colours (hues) produced, • which he noted were in the same order as that observed in a rainbow. compiled by TANVEER AHMED 12
  13. 13. Newton’s Prismatic Hues• He also appreciated that the colours were not a special property of the light but merely a sequence• of sensations perceived by the human eye. In his own words: And if at any time I speak of light and rays as coloured or endued with colours, I would be understood to speak not philosophically and properly, but grossly, and accordingly to such conceptions as vulgar people in seeing all these experiments would be apt to frame.  For the rays to speak properly are not coloured. In them is nothing else than a certain power and disposition to stir up a sensation of this or that colour. compiled by TANVEER AHMED 13
  14. 14. Electromagnetic radiationdiscovery by the astronomer Herschel (IR)• the heating effect of the rays beyond the red end of the visible spectrum, a region now referred to as – the infrared (IR). compiled by TANVEER AHMED 14
  15. 15. German physicist J W Ritter,UV• exploring the other end of the spectrum, found that silver nitrate was darkened more• rapidly by rays beyond the violet than by blue and violet radiation from the visible spectrum;• he is credited with discovering ultraviolet (UV) radiation. compiled by TANVEER AHMED 15
  16. 16. Scottish physicist and mathematician JamesClerk Maxwell In 1860• Developed a theory that predicted a whole family of wave radiations• having associated electrical• and magnetic fields,• distinguished by having a common velocity in space• but differing• in wavelength and frequency• It was more than 25 years before his prediction was confirmed. Proof was provided in 1887 by the German physicist• Heinrich Hertz compiled by TANVEER AHMED 16
  17. 17. German physicist Heinrich Hertz-1887RADIO WAVES• generating an oscillating current from the spark of• an induction coil,• produced and detected radiation of extremely long wavelengths, now known as radio waves.• Subsequently other forms of electromagnetic radiation were discovered,• leading to the realisation that the visible spectrum (from violet to red) forms only a small part of the total electromagnetic spectrum known today. compiled by TANVEER AHMED 17