Application Note (A2) LED Measurements
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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. -
About SI Units
Units SI units: International system of units (French: “SI” means “Système Internationale”) The seven SI base units are: Mass: kg Defined by the prototype “standard kilogram” located in Paris. The standard kilogram is made of Pt metal. Length: m Originally defined by the prototype “standard meter” located in Paris. Then defined as 1,650,763.73 wavelengths of the orange-red radiation of Krypton86 under certain specified conditions. (Official definition: The distance traveled by light in vacuum during a time interval of 1 / 299 792 458 of a second) Time: s The second is defined as the duration of a certain number of oscillations of radiation coming from Cs atoms. (Official definition: The second is the duration of 9,192,631,770 periods of the radiation of the hyperfine- level transition of the ground state of the Cs133 atom) Current: A Defined as the current that causes a certain force between two parallel wires. (Official definition: The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 Newton per meter of length. Temperature: K One percent of the temperature difference between boiling point and freezing point of water. (Official definition: The Kelvin, unit of thermodynamic temperature, is the fraction 1 / 273.16 of the thermodynamic temperature of the triple point of water. Amount of substance: mol The amount of a substance that contains Avogadro’s number NAvo = 6.0221 × 1023 of atoms or molecules. -
Black Body Radiation and Radiometric Parameters
Black Body Radiation and Radiometric Parameters: All materials absorb and emit radiation to some extent. A blackbody is an idealization of how materials emit and absorb radiation. It can be used as a reference for real source properties. An ideal blackbody absorbs all incident radiation and does not reflect. This is true at all wavelengths and angles of incidence. Thermodynamic principals dictates that the BB must also radiate at all ’s and angles. The basic properties of a BB can be summarized as: 1. Perfect absorber/emitter at all ’s and angles of emission/incidence. Cavity BB 2. The total radiant energy emitted is only a function of the BB temperature. 3. Emits the maximum possible radiant energy from a body at a given temperature. 4. The BB radiation field does not depend on the shape of the cavity. The radiation field must be homogeneous and isotropic. T If the radiation going from a BB of one shape to another (both at the same T) were different it would cause a cooling or heating of one or the other cavity. This would violate the 1st Law of Thermodynamics. T T A B Radiometric Parameters: 1. Solid Angle dA d r 2 where dA is the surface area of a segment of a sphere surrounding a point. r d A r is the distance from the point on the source to the sphere. The solid angle looks like a cone with a spherical cap. z r d r r sind y r sin x An element of area of a sphere 2 dA rsin d d Therefore dd sin d The full solid angle surrounding a point source is: 2 dd sind 00 2cos 0 4 Or integrating to other angles < : 21cos The unit of solid angle is steradian. -
Radiometry of Light Emitting Diodes Table of Contents
TECHNICAL GUIDE THE RADIOMETRY OF LIGHT EMITTING DIODES TABLE OF CONTENTS 1.0 Introduction . .1 2.0 What is an LED? . .1 2.1 Device Physics and Package Design . .1 2.2 Electrical Properties . .3 2.2.1 Operation at Constant Current . .3 2.2.2 Modulated or Multiplexed Operation . .3 2.2.3 Single-Shot Operation . .3 3.0 Optical Characteristics of LEDs . .3 3.1 Spectral Properties of Light Emitting Diodes . .3 3.2 Comparison of Photometers and Spectroradiometers . .5 3.3 Color and Dominant Wavelength . .6 3.4 Influence of Temperature on Radiation . .6 4.0 Radiometric and Photopic Measurements . .7 4.1 Luminous and Radiant Intensity . .7 4.2 CIE 127 . .9 4.3 Spatial Distribution Characteristics . .10 4.4 Luminous Flux and Radiant Flux . .11 5.0 Terminology . .12 5.1 Radiometric Quantities . .12 5.2 Photometric Quantities . .12 6.0 References . .13 1.0 INTRODUCTION Almost everyone is familiar with light-emitting diodes (LEDs) from their use as indicator lights and numeric displays on consumer electronic devices. The low output and lack of color options of LEDs limited the technology to these uses for some time. New LED materials and improved production processes have produced bright LEDs in colors throughout the visible spectrum, including white light. With efficacies greater than incandescent (and approaching that of fluorescent lamps) along with their durability, small size, and light weight, LEDs are finding their way into many new applications within the lighting community. These new applications have placed increasingly stringent demands on the optical characterization of LEDs, which serves as the fundamental baseline for product quality and product design. -
Laser Terms Glossary
LASER TERMS GLOSSARY Texas State University – San Marcos 2/25/07 Risk Management & Safety LASER TERMS GLOSSARY Introduction - This section lists information pertinent to laser safety. The definitions in this glossary will not cover every term associated with lasers but does cover a majority of the terms. If a term should be encountered in your work with lasers and is not in this glossary, consult your supervisor or call the Texas State University Risk Management and Safety Office. Laser Terms ABSORPTION: means the transformation of radiant energy to a different form by interaction with matter. ACCESS CONTROL: Entry must be restricted to authorized laser personnel during the operation of laser equipment. ACCESSIBLE EMISSION LIMIT (AEL): - means the maximum accessible emission level permitted within a particular class. WAVELENGTH DURATION CLASS 1 CLASS 2 CLASS 3a CLASS 3b CLASS 4 (μm) (s) (W) (W) (W) (W) (W) Ultraviolet 0.18 to 0.302 3x104 ≤ 9.6x10-9 - Between 1 to 5 > Class 3a but > 0.5 0.302 to 0.4 3x104 ≤ 3.2x10-6 times Class 1 ≤ 0.5 Visible > Class 1 Less than 5 > Class 3a but 0.4 to 0.7 10 ≤ 0.4x10-3 > 0.5 but < 0.001 times Class 2 ≤ 0.5 Near IR ≤ 0.4x10-3 Between 1 to 5 > Class 3a but 0.7 to 1.05 ≥ 10 - > 0.5 to <1.9x10-3 times Class 1 ≤ 0.5 IR 1.05 to 1.15 ≤ 1.9x10-3 ≤ 1.9x10-3 Between 1 to 5 > Class 3a but 1.15 to 1.2 ≥ 10 - > 0.5 to 1.5x10-2 times Class 1 ≤ 0.5 1.2 to 1.4 ≤ 1.5x10-2 Far IR Between 1 to 5 > Class 3a but 1.4 to 100 ≥ 10 ≤ 9.6x10-3 - > 0.5 times Class 1 ≤ 0.5 AGENCY: means the Texas Department of State Health Services Radiation Control agency. -
Radiometry and Photometry
Radiometry and Photometry Wei-Chih Wang Department of Power Mechanical Engineering National TsingHua University W. Wang Materials Covered • Radiometry - Radiant Flux - Radiant Intensity - Irradiance - Radiance • Photometry - luminous Flux - luminous Intensity - Illuminance - luminance Conversion from radiometric and photometric W. Wang Radiometry Radiometry is the detection and measurement of light waves in the optical portion of the electromagnetic spectrum which is further divided into ultraviolet, visible, and infrared light. Example of a typical radiometer 3 W. Wang Photometry All light measurement is considered radiometry with photometry being a special subset of radiometry weighted for a typical human eye response. Example of a typical photometer 4 W. Wang Human Eyes Figure shows a schematic illustration of the human eye (Encyclopedia Britannica, 1994). The inside of the eyeball is clad by the retina, which is the light-sensitive part of the eye. The illustration also shows the fovea, a cone-rich central region of the retina which affords the high acuteness of central vision. Figure also shows the cell structure of the retina including the light-sensitive rod cells and cone cells. Also shown are the ganglion cells and nerve fibers that transmit the visual information to the brain. Rod cells are more abundant and more light sensitive than cone cells. Rods are 5 sensitive over the entire visible spectrum. W. Wang There are three types of cone cells, namely cone cells sensitive in the red, green, and blue spectral range. The approximate spectral sensitivity functions of the rods and three types or cones are shown in the figure above 6 W. Wang Eye sensitivity function The conversion between radiometric and photometric units is provided by the luminous efficiency function or eye sensitivity function, V(λ). -
International System of Units （Si）
［TECHNICAL DATA］ INTERNATIONAL SYSTEM OF UNITS（ SI） Excerpts from JIS Z 8203（ 1985） 1. The International System of Units（ SI） and its usage 1－3. Integer exponents of SI units 1－1. Scope of application This standard specifies the International System of Units（ SI） and how to use units under the SI system, as well as （1） Prefixes The multiples, prefix names, and prefix symbols that compose the integer exponents of 10 for SI units are shown in Table 4. the units which are or may be used in conjunction with SI system units. Table 4. Prefixes 1 2. Terms and definitions The terminology used in this standard and the definitions thereof are as follows. － Multiple of Prefix Multiple of Prefix Multiple of Prefix （1） International System of Units（ SI） A consistent system of units adopted and recommended by the International Committee on Weights and Measures. It contains base units and supplementary units, units unit Name Symbol unit Name Symbol unit Name Symbol derived from them, and their integer exponents to the 10th power. SI is the abbreviation of System International d'Unites（ International System of Units）. 1018 Exa E 102 Hecto h 10−9 Nano n （2） SI units A general term used to describe base units, supplementary units, and derived units under the International System of Units（ SI）. 1015 Peta P 10 Deca da 10−12 Pico p （3） Base units The units shown in Table 1 are considered the base units. 1012 Tera T 10−1 Deci d 10−15 Femto f （4） Supplementary units The units shown in Table 2 below are considered the supplementary units. -
Principles of Radiation Measurement
Principles of Radiation Measurement This report presents a comprehensive summary of the terminology and units used in radiometry, photometry, and the measurement of photosynthetically active radiation (PAR). Measurement errors can arise from a number of sources, and these are explained in detail. Finally, the conversion of radiometric and photometric units to photon units is discussed. In this report, the International System of Units (SI) is used unless noted otherwise.9 Radiometry component of sunlight plus the diffuse component of skylight received together on a horizontal surface). This Radiometry1 is the measurement of the properties of physical quantity is measured by a pyranometer such as radiant energy (SI unit: joule, J), which is one of the many the LI-200R. Unit: W m-2. interchangeable forms of energy. The rate of flow of radi- ant energy, in the form of an electromagnetic wave, is Direct Solar Radiation is the radiation emitted from the called the radiant flux (unit: watt, W; 1 W = 1 J s-1). Radi- solid angle of the sun’s disc, received on a surface per- ant flux can be measured as it flows from the source (the pendicular to the axis of this cone, comprising mainly sun, in natural conditions), through one or more reflect- unscattered and unreflected solar radiation. This physical -2 ing, absorbing, scattering and transmitting media (the quantity is measured by a pyrheliometer. Unit: W m . Earth’s atmosphere, a plant canopy, etc.) to the receiving Diffuse Solar Radiation (sky radiation) is the downward surface of interest (e.g. a photosynthesizing leaf).8 scattered and reflected radiation coming from the whole hemisphere, with the exception of the solid angle sub- Terminology and Units tended by the sun’s disc. -
Glossary of Laser Terms Absorb to Transform Radiant Energy Into a Different Form, with a Resultant Rise in Temperature. Absorpt
Glossary of Laser Terms Absorb To transform radiant energy into a different form, with a resultant rise in temperature. Absorption Transformation of radiant energy to a different form of energy by the interaction with matter, depending on temperature and wavelength. Accessible Emission Level The magnitude of accessible laser (or collateral) radiation of a specific wavelength or emission duration at a particular point as measured by appropriate methods and devices. Also means radiation to which human access is possible in accordance with the definitions of the laser's hazard classification. Accessible Emission Limit (AEL) The maximum accessible emission level permitted within a particular class. In ANSI Z 136.1, AEL is determined as the product of accessible emission Maximum Permissible Exposure limit (MPE) and the area of the limiting aperture (7 mm for visible and near-infrared lasers). Aperture An opening through which radiation can pass. Argon A gas used as a laser medium. It emits blue-green light primarily at 448 and 515 nm. Attenuation The decrease in energy (or power) as a beam passes through an absorbing or scattering medium. Aversion Response Movement of the eyelid or the head to avoid an exposure to a noxious stimulant, bright light. It can occur within 0.25 seconds, and it includes the blink reflex time. Beam A collection of rays that may be parallel, convergent, or divergent. Beam Diameter The distance between diametrically opposed points in the cross section of a circular beam where the intensity is reduced by a factor of e-1 (0.368) of the peak level (for safety standards). -
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[V2C2-09P70] 2.9 Radiant Intensity
70 RADIOMETRY AND PHOTOMETRY VOL. I I 2.9 Radiant Intensity The concept of radiant intensity, the last of the set of basic radiometric concepts to be introduced in this chapter, is designed to give a measure of the solid angle density of radiant flux. Thus radiant intensity is a dual concept to irradiance in the sense that the latter gives a measure of the area density of radiant flux while the former gives a measure of the solid angle density of radiant flux. At one time the concept of radiant intensity enjoyed the place now occupied by radiant flux. In the days of the candle and gas lamp there were very few artificial extended light sources. The controlled artificial point source, such as a candle's flame, was the sole basis for radiometric standards and its radiant output was conveniently measured in terms of intensity. However, with the passing of years the numbers of extended artificial light sources increased and the classical mode of use of radiant intensity has become correspondingly less frequent than that of radiant flux. Eventually radiance for the most part usurped the once centrally disposed radiant intensity concept. Despite this displacement of radiant intensity's status, it appears that there will always exist times when its use arises naturally. For example when emitting 'point sources' are considered, the use of radiant intensity seems automatically indicated. This useful aspect of radiant intensity will be discussed during its systematic development, to which we now turn. Operational Definition of Empirical Radiant Intensity In presenting the concept of radiant intensity we shall be guided by operational considerations so as to give the concept a secure footing relative to the other radiometric concepts already defined. -
Basic Principles of Imaging and Photometry Lecture #2
Basic Principles of Imaging and Photometry Lecture #2 Thanks to Shree Nayar, Ravi Ramamoorthi, Pat Hanrahan Computer Vision: Building Machines that See Lighting Camera Physical Models Computer Scene Scene Interpretation We need to understand the Geometric and Radiometric relations between the scene and its image. A Brief History of Images 1558 Camera Obscura, Gemma Frisius, 1558 A Brief History of Images 1558 1568 Lens Based Camera Obscura, 1568 A Brief History of Images 1558 1568 1837 Still Life, Louis Jaques Mande Daguerre, 1837 A Brief History of Images 1558 1568 1837 Silicon Image Detector, 1970 1970 A Brief History of Images 1558 1568 1837 Digital Cameras 1970 1995 Geometric Optics and Image Formation TOPICS TO BE COVERED : 1) Pinhole and Perspective Projection 2) Image Formation using Lenses 3) Lens related issues Pinhole and the Perspective Projection Is an image being formed (x,y) on the screen? YES! But, not a “clear” one. screen scene image plane r =(x, y, z) y optical effective focal length, f’ z axis pinhole x r'=(x', y', f ') r' r x' x y' y = = = f ' z f ' z f ' z Magnification A(x, y, z) B y d B(x +δx, y +δy, z) optical f’ z A axis Pinhole A’ d’ x planar scene image plane B’ A'(x', y', f ') B'(x'+δx', y'+δy', f ') From perspective projection: Magnification: x' x y' y d' (δx')2 + (δy')2 f ' = = m = = = f ' z f ' z d (δx)2 + (δy)2 z x'+δx' x +δx y'+δy' y +δy = = Area f ' z f ' z image = m2 Areascene Orthographic Projection Magnification: x' = m x y' = m y When m = 1, we have orthographic projection r =(x, y, z) r'=(x', y', f ') y optical z axis x z ∆ image plane z This is possible only when z >> ∆z In other words, the range of scene depths is assumed to be much smaller than the average scene depth. -
Radiometric Quantities and Units Used in Photobiology And
Photochemistry and Photobiology, 2007, 83: 425–432 Radiometric Quantities and Units Used in Photobiology and Photochemistry: Recommendations of the Commission Internationale de l’Eclairage (International Commission on Illumination) David H. Sliney* International Commission on Illumination (CIE), Vienna, Austria and Laser ⁄ Optical Radiation Program, US Army Center for Health Promotion and Preventive Medicine, Gunpowder, MD Received 14 November 2006; accepted 16 November 2006; published online 20 November 2006 DOI: 10.1562 ⁄ 2006-11-14-RA-1081 ABSTRACT The International Commission on Illumination, the CIE, has provided international guidance in the science, termi- To characterize photobiological and photochemical phenomena, nology and measurement of light and optical radiation since standardized terms and units are required. Without a uniform set 1913. The International Lighting Vocabulary (parts of which of descriptors, much of the scientific value of publications can be are also issued as an ISO or IEC standard) has been an lost. Attempting to achieve an international consensus for a international reference for photochemists and photobiolo- common language has always been difficult, but now with truly gists for many decades; and the next revision is due to be international scientific publications, it is all the more important. published later this year or next (2). Despite its stature, As photobiology and photochemistry both represent the fusion of many research scientists are unfamiliar with some of the several scientific disciplines, it is not surprising that the physical subtle distinctions between several widely used radiometric terms used to describe exposures and dosimetric concepts can terms. Tables 1–4 provide several standardized terms that vary from author to author.