Originally presented as a Keynote to the CIE Conference, Paris, April Reproduced with the kind permission of Jean Bastie.

Transcription

1 Originally presented as a Keynote to the CIE Conference, Paris, April Reproduced with the kind permission of Jean Bastie. Dear colleagues, Diapo - 1 Celebrating the centenary of the CIE is a good opportunity to look back at its history in order to point out the major achievements which were realised during these hundred years. Although, it is usually admitted that CIE was founded in Berlin in 1913, its birth, in fact, spreads between 1900 and 1921 and Paris took a special place in this birth. Two major events took place in Paris, the creation of the Commission Internationale de Photométrie in 1900 and the first meeting of the Commission Internationale de l Eclairage in Diapo - 2 In 1900, at Paris, during the International Exhibition, the members of the International Gas Congress agreed, following a proposal of Professor Vautier, to found the Commission Internationale de Photométrie (CIP). The purpose of this commission was to determine the rules to be applied in the photometric measurements of incandescent gas burners which were the major sources of lighting at that time and the unification of screw-threads used in the gas engineering. The first meeting of the CIP took place in Zurich, in June At that meeting the Commission formulated a recommendation asking for comparison of flame lamps used as photometric standards. It also adopted a working program, the major item of which was the establishment of detailed rules for the photometry of incandescent gas lamps. The second session took place still in Zurich, in The comparison of photometric standards was confirmed and a committee was given the task of fixing the ratio between the units derived from the different flame standards. In 1881, Professor Violle had proposed an alternative to flame photometric standards based on the platinum at its freezing point. The Commission passed a resolution asking to the national laboratories that they should study the constancy of the melting point of platinum because of its importance in photometry. Diapo - 3 The third session of the CIP took place again in Zurich, in A short paper, presented by Strache of Austria-Hungary pointed out that, if the radiation from a source were weighted in accordance with the sensitivity of the eye, its measurement

2 in absolute units was, in effect, a measurement of the light from the source. That is the basis of the modern photometry. For using that photometric method it is necessary to determine the sensitivity curve of the eye. The proposals in this paper were referred to a committee for further study. Another committee was set up to study proposals for the establishment of an international system of photometric quantities and their units. At this meeting it was also recognised that the scope of the Commission s work should be widened to include all aspects of lighting. Soon after this session a committee was appointed to prepare statutes for creating the Commission Internationale de l Eclairage (CIE). The fourth session of the CIP took place in Berlin in The whole session was devoted write the statutes of the CIE and the records were never printed. The statutes were given the operative date of September 1913 which is therefore considered as the birthday of CIE. But, the numbering of the CIE sessions has always included those of the CIP. So, the first session of the CIE, numbered fifth session, was held in Paris in July At this meeting four study committees were appointed to deal with the following subjects: Heterochromatic photometry, Definitions and symbols, Lighting in factories and schools, Automobile headlights. The recommendations and decisions of CIP and CIE taken during these 21 first years were fundamental for the CIE past and present activities and the major CIE achievements are coming from them. Diapo - 4 At its first meeting, in 1903, the CIP recommended the organisation of an international comparison of the various photometric standards used at that time. This important comparison was carried out in 1904 by Parterson in England. The measurements were in good agreement and gave the following results: 1 French decimal candle = 1 English candle = nine-tenths Hefner candle used in Germany with an uncertainty of little less than 2 %. This comparison was followed by many others not only on flame standard lamps but also on carbon filament lamps. Diapo - 5 As an outcome of all these measurements the laboratories of France, Great Britain and the USA announced that from 1 st July, 1909, the American candle, the British candle and the French decimal candle would have the same value. It was added that the value of the Hefner lamp could be taken as nine-tenths of this common unit. This

3 agreement was not directly sponsored by the CIP but by the national laboratories, although it was the result of the comparisons initiated by CIP. Diapo - 6 Due to the decision to initiate a comparison between the various flame standards, there were representatives of the national laboratories of France, Germany and Great Britain at the second meeting of the CIP, in Until 1930, CIE was the sole framework in which the members of the national laboratories had the opportunity to meet and work together. In 1930, the newly appointed Consultative Committee of Electricity of the BIPM, took over the responsibility of photometric units. This topic being not fully related to electricity, a specific Consultative Committee of Photometry (CCP) was appointed in The connection between CIE and the CCP has always been very tight; most of the members of the CCP being also members of the CIE, and, works initiated at CIE had an important influence on the results and decisions of the CCP and reciprocally. Diapo - 7 For formalising the relationship between BIPM and CIE, in 2007, an agreement was signed in order to specify the specific role of each organisation and to establish rules for cooperation. Diapo -8 The comparison activity of the CIE continues in various fields until the beginning of the 90 s. In this field, CIE was a forerunner since now international comparisons are organised on a regular basis by the BIPM and the regional metrological organisations in the well established framework of the Mutual Recognition Arrangement. Diapo - 9 One of the major achievements of the CIP, then CIE, started at the third session in 1911 with the appointment of a committee for determining the sensitivity curve of the eye according to the proposal of. Strache. At the session of 1921, the first formal session of the CIE, this committee took the name of committee for heterochromatic photometry and was confirmed the task of proposing a sensitivity curve for the eye. Diapo - 10 At the following session, in 1924, following a proposal of Gibson, supported by the committee for heterochromatic photometry, the commission adopted a set of provisional values for the visibility factor. The original set of values as it appears in the proceedings of the session is given on the slide. Diapo - 11

4 The values of the V(λ) curve were endorsed by the Comité International des Poids et Mesures in The V(λ) curve is only valid for a high luminance level, the photopic vision. Also CIE published, in 1951, the V (λ) curve which is valid for a low level of luminance, the scotopic vision. Diapo - 12 The present photometric system, based on V(λ) and V (λ) is usable for photopic and scotopic vision but not for mesopic vision which covers the region in between the two others. In the recent years CIE has worked on that problem and recently published two documents introducing possible photometric systems usable over the full dynamic range of luminance. Is it a first step towards the new photometric system for the 21 st century? Diapo - 13 In its second session in 1907, according to the work carried out by professor Violle, the CIE adopted a resolution asking the national laboratories to study the possibility to realise a photometric standard base on the light emitted by the platinum at its freezing point. In its original work, schematically shown on the slide, professor Violle compared the light intensity emitted by a small surface, through a known aperture, of a freezing ingot of platinum to the light intensity of a carcel lamp used in France as photometric standard. This work has been carried-out at the Conservatoire National des Arts et Métiers, the organisation which is hosting our present meeting, somewhere in these buildings. Professor Violle was also the first president of the French national committee. Diapo - 14 Following this resolution, several national metrological laboratories undertook researches on the realisation of the candela based on these proposals. The results of these important research works led to the definition of the candela adopted by the CGPM in The drawing of the black body at the freezing point of platinum presented on the slide is the one realised by Maurice Debure also in these buildings. You are in the birth place of the French candela. In this field, as for the international comparisons, CIE was a forerunner and a visionary for photometry. Diapo - 15 In 1979 the General Conference of Weights and Measures, adopted the present definition of the candela shown on the slide. This definition derives directly from the paper presented by Strache at the third session of the CIP in Although it is not explicitly written in the definition but explained in the BIPM monograph Principles governing photometry and in

5 the CIE publication 18.2 The basis of physical photometry, that definition of the candela is based on the spectral luminous efficiency functions which have been defined by the CIE for V(λ),and for V (λ). As it has been shown, the works undertaken by the CIE since the beginning of its life and the recommendations taken at its first sessions were at the origin of the two successive definitions of the candela. Diapo - 16 At the 3 rd session held in 1911 a committee was set up to study proposals for the establishment of an international system of photometric quantities and their units. At the session of 1921 the first definitions were adopted for the three fundamental quantities, luminous flux, illumination and luminous intensity, and for their units. The picture on the slide represents the definition of the luminous intensity and its unit as it was published in the proceedings of the session. It was the beginning of the history of the international lighting vocabulary. Diapo - 17 The first committee formally in charge of the general vocabulary on illumination was established at the Geneva session in The publication of the 1 st edition of the International Lighting Vocabulary took place in The second edition, prepared in collaboration with IEC, was published in The 3 rd and 4 th editions were published respectively in 1970 and 1987 as joint publication of CIE and IEC. The last edition was published in 2011 as a CIE Standard. This last edition contains almost terms, the previous one had about 800 terms and the first one, in 1938, only 100 terms. The preparation of the International Lighting Vocabulary was and should stay a major activity of the CIE. The field of lighting is widely open on various aspects of the human activities and concerns people coming from various horizons, so speaking a common language and having terms defined of an unambiguous manner is fundamental for working together. In a world changing very quickly with the development of new technologies it is important that CIE could be able to update its vocabulary very quickly. Diapo - 18 The colorimetry became an independent topic of study at the CIE only at session of 1924 with the appointment of a specific committee coming from the committee on heterochromatic photometry. All the work done in this field is probably the most

6 important achievement of the CIE. The 2 standard observer, in connection with the CIE 1931 XYZ colour space and the standard illuminants A, B and C were adopted in 1931 at the Cambridge session. Diapo - 19 In 1964, the 10 CIE standard observer and the new standard daylight illuminant D65 were added. Another important activity of the CIE was also to define uniform colour space for determining easily colour differences. For that purpose, two colour spaces have been adopted in 1976: the CIE L*a*b* Colour Space and the CIE L*u*v* Colour Space. Diapo - 20 Although, the colorimetric system is well established and standardized the fundamental and applied researches are still very active in this field. The last CIE publications concerned the development of a chromaticity diagram based on physiological data, the colour appearance and the colour differences. Colour is only a small part of the appearance of an object and measuring the total visual appearance could become an important need for many applications in a near future. So CIE has started to look at this new field of measurements by holding a symposium on "Visual Appearance", in 2006, in Paris and appointing a technical committee to examine the various parameters which have to be considered for "measuring" the appearance. Even if the colour measurement is important for many applications it is necessary to keep also in mind that colour has a major impact on the everyday life and it is also a major component in the artistic production. Linking physical measurements of colour with psychophysical data it could be possible to find models for colour emotion and harmony. This is the task of a CIE new technical committee. These new fields of investigations on colour and appearance could become major topics of study for the 21 st century. Diapo - 21 In its first session, in 1921, CIE appointed two committees on lighting engineering : Lighting in factories and schools, and Automobile headlights. Beside the fundamental aspects of lighting, the lighting engineering has always been a major activity of the CIE from the very beginning. At the Geneva session, in 1924, the committee set-up to study the lighting in factories and schools presented a report. This report made a number of recommendations regarding the minimum values of illumination required for different kinds of work, the avoidance of glare and the provision of emergency lighting. The use of the report as a basis for regulations regarding lighting in factories and school

7 was recommended. It was the beginning of the CIE recommendations for good practice in lighting which have became later standards. Diapo - 22 At the same session in 1924, a large number of papers presenting various applications of indoor and outdoor lighting as well as lighting equipments were given. On this slide it is possible to see two photos coming from the proceedings of the session and showing for the first one, a type of portable demonstration equipment used to promote the lighting directly in the rooms to be lighted and the second a good quality street lighting, with a good uniformity. Diapo - 23 Some other types of documents were presented at this session : a luminaire with 3 incandescent lamps and its photometric curve, and a diagram of the lighting of the place d Italie in Paris showing the arrangement of luminaires and the curve of isoillumination. Diapo - 24 The use of lighting for signalling was also presented at this meeting and we can see on this slide some ancestors of the street signalling : starting from the left we have traffic light, light for runabout and light for one way street. Diapo - 25 Starting with two well defined topics, Lighting in factories and schools, and Automobile headlights the CIE activity in the field of lighting engineering, with time, has covered all the aspects of lighting. Due to the continuous and fast improvement of technologies and the modification of the needs of the users the recommendations and later standards in this field have to be regularly up-dated and it would be impossible to give an overview of all the activities in this field over 100 years. But, the well being and the safety of the users have been a permanent concern of the CIE by producing the right amount of light at the right place, using day lighting as well as electric lighting. Diapo - 26 The activity in the field of standardisation starts at the very beginning of the CIP, in 1900, since, among the two tasks entrusted to it, one was the unification of screwthreads used in the gas engineering. During a long period of time CIE has written various high level documents. Most of them were fundamental documents widely used by regulating bodies even if they have not the formal name of standard. Due to the increasing importance of standardisation in trade and industry and the need of formal standards in the fields of lighting it became evident that CIE has a specific role to play in that activity. CIE signed an agreement with the International

8 Standardising Organisation, ISO in 1989, and, latter, in 1992, with the International Electrotechnical Commission, IEC. This agreement recognises CIE as an official standardising body for the light and lighting matters. It gives CIE the possibility to publish standards on its own authority but also to have some of these standards adopted by ISO or IEC and published jointly by both organisations. Until now 37 standards have been published by CIE, 29 of them jointly with ISO or IEC and several others are in preparation. Diapo - 27 Since the beginning of CIP and CIE technologies used for lighting has undergone dramatic evolution starting with gas lighting widely in use at the creation of the CIP, followed by incandescent lighting and fluorescent lighting using various types of sources and, now, solid state lighting which is growing very quickly. But in spite of the evolution of sciences and techniques over a century the principles which have motivated the creation of the CIE are still valid. These principles could be summarized by : To give to the international community working in the field of lighting the opportunity to meet and to work together and to use the same language and the same references in order to understand each other. To define the rules for realising the best possible lighting with the available technologies at a time, for the wellbeing and the safety of people. Diapo - 28 The scientific subjects which have been recommended for study at the very beginning of CIE have come out as major achievements. Among them we could remind all the works done on vision and the visual system which have established the basis of photometry and colorimetry, and on the physical properties of radiation which have led to the implementation of the system of quantities and units used in optical radiation measurements. In many fields of activities CIE was a forerunner and its members were visionary of what will be the needs for the future. Now CIE has to continue according to the spirit of its predecessors... Diapo towards a new century of light. Diapo 30