Standard illuminants
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Standard illuminants

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Standard illuminants Standard illuminants Presentation Transcript

  • Standard illuminants 1COMMISSION INTERNATIONALE DE L’ÉCLAIRAGE (CIE) IN 1931 IT WAS RECOGNISED THAT STANDARDISED SOURCES OF ILLUMINATION COMPILED BY TANVEER AHMED
  • Standard illuminants TABLE OF CONTENT 21. Commission Internationale de l’Éclairage (CIE)2. Standard illuminant A3. Standard illuminant B4. Standard illuminant C5. Standard illuminant D6. standard illuminant D Hunt SuggestionsCOMPILED BY TANVEER AHMED
  • Commission Internationale de l’Éclairage (CIE) When the international system of colour measurement and specification was set up by  the Commission Internationale de l’Éclairage (CIE) in 1931 it was recognised that standardised sources of illumination would have to be defined,  and three such sources  (CIE Standard sources A, B and C) were adopted at that time as approximations to three common illumination conditions. 3 COMPILED BY TANVEER AHMED
  • Commission Internationale de l’Éclairage (CIE) Although these sources were defined in such a way that they could be  physically realised (a standardised tungsten lamp  in combination with suitable blue-coloured solution filters) the opportunity was also taken to define  a set of numerical values  representing the relative SPD of the appropriate standard  illuminant  at 10 nm intervals across the visible spectrum (380–770 nm). 4 COMPILED BY TANVEER AHMED
  • It is thus important to distinguish between standard illuminants,which are defined 5in terms of spectral power distributions,and standard sources,which are defined asphysically realizable emitters of radiant energyand have SPDs that only approximate to those of thecorresponding illuminants.COMPILED BY TANVEER AHMED
  • Standard illuminant A 6 was designed in 1931 to be representative  of indoor artificial  (tungsten lamp) illumination  and is defined as an illuminant having the same SPD as a  Planckian radiator  at a temperature of about 2856 K. An actual source corresponding to this illuminant is readily achieved,COMPILED BY TANVEER AHMED
  • Standard illuminant A 7 and calibrated standard tungsten lamps are available  from standardising bodies in each country; in the UK this is the National Physical Laboratory (NPL). Such an illuminant is relatively yellowish in colour as it is deficient in power in the blue end of the visible spectrum and rich in the red wavelengths (Figure 1.9).COMPILED BY TANVEER AHMED
  • SPDs of CIE standard illuminants 8COMPILED BY TANVEER AHMED
  • Standard illuminant B 9 with a correlated colour temperature (CCT) of about 4870 K, was supposed to represent daylight plus sunlight,COMPILED BY TANVEER AHMED
  • standard illuminant C 10 (CCT = 6770 K) was intended to represent average daylight; both are now largely redundant in favour of the D illuminants introduced subsequently.COMPILED BY TANVEER AHMED
  • standard illuminant D 11 In 1963, therefore, the CIE recommended several new standard illuminants (the D illuminants) by defining spectral distributions across the UV, visible and near-IR (300–830 nm) to represent various phases of daylight. CIE illuminant D65, with an approximate CCT of 6500 K, is now accepted by the CIE as a standard illuminant (CIE 1986).COMPILED BY TANVEER AHMED
  • standard illuminant D 12 Its SPD is a good approximation • of average daylight, taking into account the following types of variation:  – from early morning to late evening  – from a blue sky to completely overcast conditions  – at different latitudes. The SPDs of the standard D illuminants were originally defined at 10 nm intervals but values at 5 nm and 1 nm intervals have been obtained by interpolation and are now available (CIE 1971 and 1986).COMPILED BY TANVEER AHMED
  • standard illuminant D 13 Figure 1.9 compares the SPD of standard illuminant D65 with the CIE illuminants A, B and C; the higher UV content of D65 compared with CIE illuminants B and C is clearly evident.COMPILED BY TANVEER AHMED
  • standard illuminant D 14 The CIE recognised that a single distribution such as  D65 would be unlikely to satisfy all colour users  and suggested others, such as D50 and D55  with CCTs of 5000 and 5500 K for use where yellower phases of daylight than average were desirable  (D50 is favoured by the graphic art trade for illumination of colour prints and photographs). D75, with a CCT of 7500 K, is popular in some parts of America for colour assessment where a bluer phase of daylight is preferred.COMPILED BY TANVEER AHMED
  • standard illuminant D 15 Although the CIE has published a method for assessing the quality of daylight simulators • for colorimetry problems have been encountered in attempts to manufacture • practical sources • that simulate the illuminant D curves, particularly the undulations present naturally and accentuated by the interpolation procedures.COMPILED BY TANVEER AHMED
  • standard illuminant D Hunt has suggested 16 Recently Hunt has suggested that the CIE needs to accept that • only approximations to the standard D illuminant curves are ever going to be possible. He advocates that practical D sources be carefully specified and adopted for use as • the best approximations to the D illuminants achievable and suggests these could be distinguished as: source DT: a tungsten–halogen lamp with a blue glass filter source DX: a filtered xenon arc source DF: a fluorescent lamp with a suitable CCT.COMPILED BY TANVEER AHMED
  • Studies of daylight and its spectrum in the 1950s and early 1960s 17 Studies of daylight and its spectrum in the 1950s and early 1960s confirmed that standard illuminants B and C had too little power in the UV region to be of value in assessing  fluorescent brightening agents  (or optical brighteners as they were then termed),  and the SPDs  and the colour coordinates also deviated from those of the natural daylight conditions they were supposed to represent.COMPILED BY TANVEER AHMED
  • Studies of daylight 18 The demand for a practical and standard D source is now substantial, both in connection with the comparison of the quality of instrumentally measured and visually assessed colour matches and also, more particularly, in the measurement and assessment of fluorescent samples  (where the UV content of the source is critical). The situation has been conveniently summarized recently by McCamyCOMPILED BY TANVEER AHMED