Standard illuminants

Application of the latest illumination standard of the IESNA (www.iesna.org). 

Reference Sample Preparation Temper- Presentation Illumination/ Standard Instru- Measure-... 

Fig.l. The approach to steady state on A, B multiflash illumination. Standard reaction medium and mediators, 180 mV, plus A, 0.01 mM antimycin to allow calibration of changes, time full scale 500 ms... 

Illumination Levels Illumination standards determine the amount of light suitable for various tasks. The type of task defines most illumination standards. Some standards include adjustment factors for age, speed, or accuracy and reflectance of the task background. Table 20-1 provides an example of recommended illumination levels for interior lighting. They may not apply to a specific location. Standards that apply locally may have variances for other factors, such as types of lighting sources. Sources of lighting include incandescent, florescent, mercury vapor, sodium vapor, and LED. The purpose here is to develop some familiarity with the stracture and content of some illumination recommendations. 

Each segment of the insulated wire and cable industry has its own set of standards, and cables are built to conform to specifications provided by a large variety of technical associations such as The Institute of Electrical Electronic Engineers (IEEE), The Insulated Cable Engineers Association, (ICEA), National Electrical Manufacturers Association (NEMA), Underwriters Laboratories (UL), Rural Electrification Administration of the U.S. Department of Agriculture (REA), Association of Edison Illumination Companies (AEIC), MiUtary Specifications of the Department of Defense (MIL), American Society for Testing and Materials (ASTM), National Electrical Code (NEC), etc. 

The International Commission on Illumination (abbreviated CIE from the Erench expression) over the years has recommended a series of methods and standards ia the field of color for a history of this process see Reference 8. 

When considering light of a certain spectral energy distribution falling on an object with a given spectral reflectance and perceived by an eye with its own spectral response, to obtain the perceived color stimulus it is necessary to multiply these factors together as ia Eigure 6. Standards are clearly required for both the observer and the illuminant. 

Fig. 11. Energy distributions of CIE standard illuminant A, a tungsten incandescent lamp a cool white fluorescent lamp E and CIE standard illuminant...

Clearly, standardized light sources are desirable for color matching, particularly in view of the phenomenon of illuminant metamerism described below. Over the years CIE has defined several standard illuminants, some of which can be closely approximated by practical sources. In 1931 there was Source A, defined as a tungsten filament incandescent lamp at a color temperature of 2854 K. Sources B and C used filtering of A to simulate noon sunlight and north sky daylight, respectively. Subsequently a series of D illuminants was estabUshed to better represent natural daylight. Of these the most important is Illuminant E). ... 

Hunter L,a,b and Other Color Spaces. The CIELAB and CIELUV color spaces were the outgrowth of a large and complex group of interrelated early systems and have replaced essentially all of them except for the 1942 Hunter Y,a,b group of color spaces (3). This was the earliest practical opponent-based system which is still widely used. In this system, for illuminant C and the 2° standard observer ... 

Eig. 14. Blackbody colors shown on a chromaticity diagram the asterisk is standard illuminant at 650 K (5). 

Plunger-type colorimeters. The plunger-type of colorimeter with two halves of the field of view illuminated by the light passing through the unknown and standard solutions respectively was invented by J. Duboscq of Paris in 1854. Various improved modifications of the instrument were subsequently developed by manufacturers of optical apparatus. 

Objective Evaluation of Color. In recent years a method has been devised and internationally adopted (International Commission on Illumination, I.C.I.) that makes possible objective specification of color in terms of equivalent stimuli. It provides a common language for description of the color of an object illuminated by a standard illuminant and viewed by a standard observer (H). Reflectance spectro-photometric curves, such as those described above, provide the necessary data. The results are expressed in one of two systems the tristimulus system in which the equivalent stimulus is a mixture of three standard primaries, or the heterogeneous-homogeneous system in which the equivalent stimulus is a mixture of light from a standard heterogeneous illuminant and a pure spectrum color (dominant wave-length-purity system). These systems provide a means of expressing the objective time-constant spectrophotometric results in numerical form, more suitable for tabulation and correlation studies. In the application to food work, the necessary experimental data have been obtained with spectrophotometers or certain photoelectric colorimeters. 

The Munsell book standards corresponding to the limiting colors may even serve as material standards for industrial color control. In a material standard system the sample is compared with a standard by eye without the use of any meter or optical instrument. The success and popularity of these systems are largely due to their simplicity of application. The ability of the human eye to compensate for various illuminants and surroundings makes it possible for this system to give results even under mediocre conditions. The most critical work with material standards requires carefully controlled observing conditions. 

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