Fundamentals of Radiometry & Photometry
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Radiometric and Photometric Concepts Based on Measurement Techniques C
Application Note No. 6 April 1982 Radiometric and Photometric Concepts Based on Measurement Techniques C. Richard Duda Senior Scientist, United Detector Technology 3939 Lanmark Street, Culver City, Cal. 90230 Abstract The value of the fundamental quality in radiometry, the bution of optical radiation. In 1937 the National Bureau watt, is presently realized by electrical substitution in of Standards transferred the luminous intensity produced which the temperature produced in a blackened mate- by a platinium blackbody to a series of lamps. This orig- rial due to absorption of radiant energy is balanced inal calibration has served to this date for standardiza- against that produced by electrical energy whose cur- tion of lamps used by industry to realize the photometric rent and voltage can accurately be measured. A new scale. Recently the fundamental unit in photometry was method to measure optical radiation is being explored changed from the candela, as defined by a blackbody, to by the National Bureau of Standards in which photons the lumen, as defined by the watt, uniting the conceptual are absorbed in a semiconductor and converted with ef- interrelationships between photometry and radiometry. 1 ficiency closely approaching the theoretical maximum Changes in the photometric scale due to redefinition of - 100 percent. its less than one percent difference in NBS lamp inten- sity values. 2 Other radiometric concepts, such as radiance, irradi- ance, and radiant intensity can easily be defined through Because Vλ , the mathematical representations of human simple geometric relationships. Photometry on the other visual spectral response is difficult to realize with a high hand, while sharing these identical relationships also in- degree of accuracy in a practical detector, comparison troduces detector response modeled after human visual of sources with a broad spectral distribution can best be traits; new measurement unit names, and reliance on accomplished with a reference source. -
CIE Technical Note 004:2016
TECHNICAL NOTE The Use of Terms and Units in Photometry – Implementation of the CIE System for Mesopic Photometry CIE TN 004:2016 CIE TN 004:2016 CIE Technical Notes (TN) are short technical papers summarizing information of fundamental importance to CIE Members and other stakeholders, which either have been prepared by a TC, in which case they will usually form only a part of the outputs from that TC, or through the auspices of a Reportership established for the purpose in response to a need identified by a Division or Divisions. This Technical Note has been prepared by CIE Technical Committee 2-65 of Division 2 “Physical Measurement of Light and Radiation" and has been approved by the Board of Administration as well as by Division 2 of the Commission Internationale de l'Eclairage. The document reports on current knowledge and experience within the specific field of light and lighting described, and is intended to be used by the CIE membership and other interested parties. It should be noted, however, that the status of this document is advisory and not mandatory. Any mention of organizations or products does not imply endorsement by the CIE. Whilst every care has been taken in the compilation of any lists, up to the time of going to press, these may not be comprehensive. CIE 2016 - All rights reserved II CIE, All rights reserved CIE TN 004:2016 The following members of TC 2-65 “Photometric measurements in the mesopic range“ took part in the preparation of this Technical Note. The committee comes under Division 2 “Physical measurement of light and radiation”. -
Luminance Requirements for Lighted Signage
Luminance Requirements for Lighted Signage Jean Paul Freyssinier, Nadarajah Narendran, John D. Bullough Lighting Research Center Rensselaer Polytechnic Institute, Troy, NY 12180 www.lrc.rpi.edu Freyssinier, J.P., N. Narendran, and J.D. Bullough. 2006. Luminance requirements for lighted signage. Sixth International Conference on Solid State Lighting, Proceedings of SPIE 6337, 63371M. Copyright 2006 Society of Photo-Optical Instrumentation Engineers. This paper was published in the Sixth International Conference on Solid State Lighting, Proceedings of SPIE and is made available as an electronic preprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. Luminance Requirements for Lighted Signage Jean Paul Freyssinier*, Nadarajah Narendran, John D. Bullough Lighting Research Center, Rensselaer Polytechnic Institute, 21 Union Street, Troy, NY 12180 USA ABSTRACT Light-emitting diode (LED) technology is presently targeted to displace traditional light sources in backlighted signage. The literature shows that brightness and contrast are perhaps the two most important elements of a sign that determine its attention-getting capabilities and its legibility. Presently, there are no luminance standards for signage, and the practice of developing brighter signs to compete with signs in adjacent businesses is becoming more commonplace. Sign luminances in such cases may far exceed what people usually need for identifying and reading a sign. Furthermore, the practice of higher sign luminance than needed has many negative consequences, including higher energy use and light pollution. -
Report on Digital Sign Brightness
REPORT ON DIGITAL SIGN BRIGHTNESS Prepared for the Nevada State Department of Transportation, Washoe County, City of Reno and City of Sparks By Jerry Wachtel, President, The Veridian Group, Inc., Berkeley, CA November 2014 1 Table of Contents PART 1 ......................................................................................................................... 3 Introduction. ................................................................................................................ 3 Background. ................................................................................................................. 3 Key Terms and Definitions. .......................................................................................... 4 Luminance. .................................................................................................................................................................... 4 Illuminance. .................................................................................................................................................................. 5 Reflected Light vs. Emitted Light (Traditional Signs vs. Electronic Signs). ...................................... 5 Measuring Luminance and Illuminance ........................................................................ 6 Measuring Luminance. ............................................................................................................................................. 6 Measuring Illuminance. .......................................................................................................................................... -
Lecture 3: the Sensor
4.430 Daylighting Human Eye ‘HDR the old fashioned way’ (Niemasz) Massachusetts Institute of Technology ChriChristoph RstophReeiinhartnhart Department of Architecture 4.4.430 The430The SeSensnsoror Building Technology Program Happy Valentine’s Day Sun Shining on a Praline Box on February 14th at 9.30 AM in Boston. 1 Happy Valentine’s Day Falsecolor luminance map Light and Human Vision 2 Human Eye Outside view of a human eye Ophtalmogram of a human retina Retina has three types of photoreceptors: Cones, Rods and Ganglion Cells Day and Night Vision Photopic (DaytimeVision): The cones of the eye are of three different types representing the three primary colors, red, green and blue (>3 cd/m2). Scotopic (Night Vision): The rods are repsonsible for night and peripheral vision (< 0.001 cd/m2). Mesopic (Dim Light Vision): occurs when the light levels are low but one can still see color (between 0.001 and 3 cd/m2). 3 VisibleRange Daylighting Hanbook (Reinhart) The human eye can see across twelve orders of magnitude. We can adapt to about 10 orders of magnitude at a time via the iris. Larger ranges take time and require ‘neural adaptation’. Transition Spaces Outside Atrium Circulation Area Final destination 4 Luminous Response Curve of the Human Eye What is daylight? Daylight is the visible part of the electromagnetic spectrum that lies between 380 and 780 nm. UV blue green yellow orange red IR 380 450 500 550 600 650 700 750 wave length (nm) 5 Photometric Quantities Characterize how a space is perceived. Illuminance Luminous Flux Luminance Luminous Intensity Luminous Intensity [Candela] ~ 1 candela Courtesy of Matthew Bowden at www.digitallyrefreshing.com. -
Foot-Candles: Photometric Units
UPDATED EXTRACT FROM CREG JOURNAL. FILE: FOOT3-UP.DOC REV. 8. LAST SAVED: 01/02/01 15:14 PHOTOMETRICS Foot-Candles: Photometric Units More footnotes on optical topics. David Gibson describes the confusing range of photometric units. A discussion of photometric units may the ratio of luminous efficiency to luminous The non-SI unit mean spherical candle- seem out of place in an electronic journal but efficiency at the wavelength where the eye is power is the intensity of a source if its light engineers frequently have to use light sources most sensitive. Unfortunately, however, this output were spread evenly in all directions. It and detectors. The units of photometry are term can be confused with the term efficacy, is therefore equivalent to the flux [lm] ¸ 4p. some of the most confusing and least which is used to describe the efficiency at standardised of units. converting electrical to luminous power. Luminance Photometric units are not difficult to The candela measures the intensity of a understand, but can be a minefield to the Illumination, Luminous Emittance. point source. We also need to define the uninitiated since many non-SI units are still The illumination of a surface is the properties of an extended source. Each small in use, and there are subtle differences incident power flux density measured in element DS of a diffuse reflective surface will between quantities with similar names, such lumens per square metre. A formal definition scatter the incident flux DF and behave as if as illumination and luminance. would be along the lines of: if a flux DF is it were an infinitesimal point source. -
Fundametals of Rendering - Radiometry / Photometry
Fundametals of Rendering - Radiometry / Photometry “Physically Based Rendering” by Pharr & Humphreys •Chapter 5: Color and Radiometry •Chapter 6: Camera Models - we won’t cover this in class 782 Realistic Rendering • Determination of Intensity • Mechanisms – Emittance (+) – Absorption (-) – Scattering (+) (single vs. multiple) • Cameras or retinas record quantity of light 782 Pertinent Questions • Nature of light and how it is: – Measured – Characterized / recorded • (local) reflection of light • (global) spatial distribution of light 782 Electromagnetic spectrum 782 Spectral Power Distributions e.g., Fluorescent Lamps 782 Tristimulus Theory of Color Metamers: SPDs that appear the same visually Color matching functions of standard human observer International Commision on Illumination, or CIE, of 1931 “These color matching functions are the amounts of three standard monochromatic primaries needed to match the monochromatic test primary at the wavelength shown on the horizontal scale.” from Wikipedia “CIE 1931 Color Space” 782 Optics Three views •Geometrical or ray – Traditional graphics – Reflection, refraction – Optical system design •Physical or wave – Dispersion, interference – Interaction of objects of size comparable to wavelength •Quantum or photon optics – Interaction of light with atoms and molecules 782 What Is Light ? • Light - particle model (Newton) – Light travels in straight lines – Light can travel through a vacuum (waves need a medium to travel in) – Quantum amount of energy • Light – wave model (Huygens): electromagnetic radiation: sinusiodal wave formed coupled electric (E) and magnetic (H) fields 782 Nature of Light • Wave-particle duality – Light has some wave properties: frequency, phase, orientation – Light has some quantum particle properties: quantum packets (photons). • Dimensions of light – Amplitude or Intensity – Frequency – Phase – Polarization 782 Nature of Light • Coherence - Refers to frequencies of waves • Laser light waves have uniform frequency • Natural light is incoherent- waves are multiple frequencies, and random in phase. -
Exposure Metering and Zone System Calibration
Exposure Metering Relating Subject Lighting to Film Exposure By Jeff Conrad A photographic exposure meter measures subject lighting and indicates camera settings that nominally result in the best exposure of the film. The meter calibration establishes the relationship between subject lighting and those camera settings; the photographer’s skill and metering technique determine whether the camera settings ultimately produce a satisfactory image. Historically, the “best” exposure was determined subjectively by examining many photographs of different types of scenes with different lighting levels. Common practice was to use wide-angle averaging reflected-light meters, and it was found that setting the calibration to render the average of scene luminance as a medium tone resulted in the “best” exposure for many situations. Current calibration standards continue that practice, although wide-angle average metering largely has given way to other metering tech- niques. In most cases, an incident-light meter will cause a medium tone to be rendered as a medium tone, and a reflected-light meter will cause whatever is metered to be rendered as a medium tone. What constitutes a “medium tone” depends on many factors, including film processing, image postprocessing, and, when appropriate, the printing process. More often than not, a “medium tone” will not exactly match the original medium tone in the subject. In many cases, an exact match isn’t necessary—unless the original subject is available for direct comparison, the viewer of the image will be none the wiser. It’s often stated that meters are “calibrated to an 18% reflectance,” usually without much thought given to what the statement means. -
Spectral Light Measuring
Spectral Light Measuring 1 Precision GOSSEN Foto- und Lichtmesstechnik – Your Guarantee for Precision and Quality GOSSEN Foto- und Lichtmesstechnik is specialized in the measurement of light, and has decades of experience in its chosen field. Continuous innovation is the answer to rapidly changing technologies, regulations and markets. Outstanding product quality is assured by means of a certified quality management system in accordance with ISO 9001. LED – Light of the Future The GOSSEN Light Lab LED technology has experience rapid growth in recent years thanks to the offers calibration services, for our own products, as well as for products from development of LEDs with very high light efficiency. This is being pushed by other manufacturers, and issues factory calibration certificates. The optical the ban on conventional light bulbs with low energy efficiency, as well as an table used for this purpose is subject to strict test equipment monitoring, and ever increasing energy-saving mentality and environmental awareness. LEDs is traced back to the PTB in Braunschweig, Germany (German Federal Institute have long since gone beyond their previous status as effects lighting and are of Physics and Metrology). Aside from the PTB, our lab is the first in Germany being used for display illumination, LED displays and lamps. Modern means to be accredited for illuminance by DAkkS (German accreditation authority), of transportation, signal systems and street lights, as well as indoor and and is thus authorized to issue internationally recognized DAkkS calibration outdoor lighting, are no longer conceivable without them. The brightness and certificates. This assures that acquired measured values comply with official color of LEDs vary due to manufacturing processes, for which reason they regulations and, as a rule, stand up to legal argumentation. -
Variable Star Photometry with a DSLR Camera
Variable star photometry with a DSLR camera Des Loughney Introduction now be studied. I have used the method to create lightcurves of stars with an amplitude of under 0.2 magnitudes. In recent years it has been found that a digital single lens reflex (DSLR) camera is capable of accurate unfiltered pho- tometry as well as V-filter photometry.1 Undriven cameras, Equipment with appropriate quality lenses, can do photometry down to magnitude 10. Driven cameras, using exposures of up to 30 seconds, can allow photometry to mag 12. Canon 350D/450D DSLR cameras are suitable for photome- The cameras are not as sensitive or as accurate as CCD try. My experiments suggest that the cameras should be cameras primarily because they are not cooled. They do, used with quality lenses of at least 50mm aperture. This however, share some of the advantages of a CCD as they allows sufficient light to be gathered over the range of have a linear response over a large portion of their range1 exposures that are possible with an undriven camera. For and their digital data can be accepted by software pro- bright stars (over mag 3) lenses of smaller aperture can be grammes such as AIP4WIN.2 They also have their own ad- used. I use two excellent Canon lenses of fixed focal length. vantages as their fields of view are relatively large. This makes One is the 85mm f1.8 lens which has an aperture of 52mm. variable stars easy to find and an image can sometimes in- This allows undriven photometry down to mag 8. -
Chapter 4 Introduction to Stellar Photometry
Chapter 4 Introduction to stellar photometry Goal-of-the-Day Understand the concept of stellar photometry and how it can be measured from astro- nomical observations. 4.1 Essential preparation Exercise 4.1 (a) Have a look at www.astro.keele.ac.uk/astrolab/results/week03/week03.pdf. 4.2 Fluxes and magnitudes Photometry is a technique in astronomy concerned with measuring the brightness of an astronomical object’s electromagnetic radiation. This brightness of a star is given by the flux F : the photon energy which passes through a unit of area within a unit of time. The flux density, Fν or Fλ, is the flux per unit of frequency or per unit of wavelength, respectively: these are related to each other by: Fνdν = Fλdλ (4.1) | | | | Whilst the total light output from a star — the bolometric luminosity — is linked to the flux, measurements of a star’s brightness are usually obtained within a limited frequency or wavelength range (the photometric band) and are therefore more directly linked to the flux density. Because the measured flux densities of stars are often weak, especially at infrared and radio wavelengths where the photons are not very energetic, the flux density is sometimes expressed in Jansky, where 1 Jy = 10−26 W m−2 Hz−1. However, it is still very common to express the brightness of a star by the ancient clas- sification of magnitude. Around 120 BC, the Greek astronomer Hipparcos ordered stars in six classes, depending on the moment at which these stars became first visible during evening twilight: the brightest stars were of the first class, and the faintest stars were of the sixth class. -
Photometric Calibrations —————————————————————————
NIST Special Publication 250-37 NIST MEASUREMENT SERVICES: PHOTOMETRIC CALIBRATIONS ————————————————————————— Yoshihiro Ohno Optical Technology Division Physics Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 Supersedes SP250-15 Reprint with changes July 1997 ————————————————————————— U.S. DEPARTMENT OF COMMERCE William M. Daley, Secretary Technology Administration Gary R. Bachula, Acting Under Secretary for Technology National Institute of Standards and Technology Robert E. Hebner, Acting Director PREFACE The calibration and related measurement services of the National Institute of Standards and Technology are intended to assist the makers and users of precision measuring instruments in achieving the highest possible levels of accuracy, quality, and productivity. NIST offers over 300 different calibrations, special tests, and measurement assurance services. These services allow customers to directly link their measurement systems to measurement systems and standards maintained by NIST. These services are offered to the public and private organizations alike. They are described in NIST Special Publication (SP) 250, NIST Calibration Services Users Guide. The Users Guide is supplemented by a number of Special Publications (designated as the “SP250 Series”) that provide detailed descriptions of the important features of specific NIST calibration services. These documents provide a description of the: (1) specifications for the services; (2) design philosophy and theory; (3) NIST measurement system; (4) NIST operational procedures; (5) assessment of the measurement uncertainty including random and systematic errors and an error budget; and (6) internal quality control procedures used by NIST. These documents will present more detail than can be given in NIST calibration reports, or than is generally allowed in articles in scientific journals. In the past, NIST has published such information in a variety of ways.