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Investigative photometry experiment on planar extended-light sources
Abstract
The inverse-square decay law of illuminance of a point light source with distance is a common notion of basic optics theory, which is readily demonstrated to be a direct consequence of the propagation of spherical wave fronts with centre at the light source. It is far less common to address the experimental verification of this law and, even less, to study the illuminance decay with distance of extended light sources, which represent somehow an unknown topic. We propose a scientific experiment where the light sensor of a smartphone is used to collect illuminance data as a function of the source-to-sensor distance and orientation. Through this procedure, students can realize the limit of validity of the inverse-square law and determine the luminance flux of the chosen point-like light source (e.g. the white LED flashlight of a smartphone). More interestingly, when dealing with extended sources (e.g. the LCD of a laptop displaying a white image) subtle characteristics of the decay trend emerge, particularly for distances lower that the source size. A detailed analysis of these characteristics is presented though a process allowing student engagement in a real scientific investigation, envisaging steps of data acquisition through experimental measurements, model construction on the basis of the observed patterns, and finally model testing. We provide a guided formulation for the general modelling of planar emitters, starting from the theoretical treatment of Lambertian sources. In this way, students are able to quantify the luminous emission also for extended sources and their deviation from a Lambertian behaviour.
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This paper proposes a 7T2C pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays using low-temperature poly-crystalline silicon (LTPS) thin-film transistors (TFTs) with two key features: high luminance uniformity and low flicker at a wide range of variable frame rates (VFRs). To achieve a high luminance uniformity, the proposed pixel circuit simultaneously compensates for the threshold voltage variation and subthreshold slope variation of the driving TFT with a sufficient compensation time regardless of the frame rate. Furthermore, flicker is reduced by employing a ramping reference voltage and current blocking method, which reduces the effect of the leakage current of TFTs and OLED capacitance, respectively. Therefore, these techniques reduce spatial emission current errors (ECEs) and temporal ECEs, enabling the circuit to be used in the VFR from 15 Hz to 360 Hz. The proposed pixel circuit was verified with unit sub-pixels designed for a 14-inch 3840×2160 (4K) AMOLED display. The worst-case spatial ECEs of the proposed 7T2C pixel circuit at the frame rate of 360 Hz were measured as +4.1/-4.2 and +1.2/-1.1 LSB at the 255th and 15th gray levels, respectively. They show better luminance uniformity compared to those of the conventional 7T1C pixel circuit, which were measured as +6.1/-8.9 and +3.6/-3.6 LSB. Furthermore, the worst-case temporal ECEs at the frame rate of 15 Hz that shows flicker performance was measured as -0.3 and -3.2 LSB at the 15th and 255th gray levels, respectively, and they are better than those of the 7T1C pixel circuit, which show 11.2 and 2.41 LSB.
In traditional optics education, shadows are often regarded as a mere triviality, namely as silhouettes of obstacles to the propagation of light. However, by examining a series of shadow phenomena from an embedded perspective, we challenge this view and demonstrate how in general both the shape of object and light source have significant impact on the resulting soft shadow images. Through experimental and mathematical analysis of the imaging properties of inverse objects, we develop a generalized concept of shadow images as complementary phenomena. Shadow images are instructive examples of optical convolution and provide an opportunity to learn about the power of embedded perspective for the study of optical phenomena in the classroom. Additionally, we introduce the less known phenomenon of the bright shadow.
Ray optics is a staple of introductory physics classes, but many students do not have the opportunity to explore optics beyond the thin lens equation. In this paper, we expand upon a successful remote experiment using a smartphone camera to explore both the successes and limitations of the thin lens equation. Application of the thin lens equation reveals a linear relationship between the object distance and the inverse image height in pixels. Using the open-source image analysis tool ImageJ to measure the image height, we can find the effective focal length of the smartphone camera lens. Our measured focal lengths agree well with the stated manufacturer values for the effective focal lengths. Further application of the thin lens equation is not successful, but a modification of the analysis leads to an explanation and experimental determination of the location of the principal planes in the smartphone camera systems. This experiment can work well at the introductory level, either in person or remote, and can be used as an introduction or motivation to explore more advanced topics in ray optics.
This Resource Letter provides a guide to the literature on teaching experimental physics using sensors in tablets, smartphones, and some specialized devices. After a general discussion of hardware (sensors) and software (apps), we present resources for experiments using mobile-device sensors in many areas of physics education: mechanics, oscillations and waves, optics, electromagnetism, matter, modern physics, and astronomy.
In times of the explosion of distance learning, because of emergency due to the pandemic, smartphone sensors and cameras are extremely valuable for teachers as they allow students to perform significant experimental activities in their own homes. The open-source software Tracker can be used in combination with the smartphone camera to perform measurements not only of mechanics activities, but also of optics. In the latter case, it is not always easy for students to understand how the pixel brightness which can be inferred from the taken photos are related to actual physical light intensity. In this paper we present a simple experiment to verify the exponential decay in the intensity of light going through successive sheets of a material (the Lambert law) with two different methods, i.e. using either the smartphone light sensor or the smartphone camera and Tracker. Besides its theoretical significance, the experiment constitutes a useful tool for calibrating the camera/Tracker combination to use it for different experiments.
In this paper we derive and analyse the expressions to find the illuminance from luminous ball, disc and line in the case of general position of the light receiver. We show that one can always replace a luminous ball with a point light source located at its center and having the appropriate luminous intensity. Any luminous disc or line can be considered, with reasonable accuracy (the relative error in the determination of the illuminance is less than ), as the point light source with anisotropic (cosine) luminous intensity and placed at their center, if the distance to the observation point is approximately four times larger than their characteristic sizes. The issues outlined in this article will be useful for undergraduate students, who study the basics of photometry.
This work provides an approach for simplifying and teaching of the confusing topic of Polarisation of light and relating Malus's Law. Teaching Polarisation and the Malus's Law are modestly achieved by means of smartphones with a convenient light meter application. The apparatus is designed so that the polarizer, the analyser, the laser light source and the smartphone are precisely aligned on a rail. During the performance, the angle of the analyser is basically varied with respect to the polariser and the transmitted light intensity is measured by the light meter application. The results clearly show that the transmitted light intensity is directly proportional to the squared polarization angle. The approach surely provides accessibility for physics teachers and would help students to learn and internalize Polarisation and relating Malus's Law in a better manner.
Many instructional physics labs are shifting to teach experimentation skills, rather than to demonstrate or confirm canonical physics phenomena. Our previous work found that many students engage in questionable research practices in attempts to confirm the canonical physics phenomena, even when confirmation is explicitly not the goal of the lab. This exploratory study aimed to answer three research questions: (RQ1) What are students’ expectations about the purpose of labs when they enter introductory physics?, (RQ2) How do their prior experiences shape those expectations?, (RQ3) In what ways do those expectations relate to their engagement in questionable research practices? Through open-response surveys, we found that students overwhelmingly expressed confirmatory beliefs about the purpose of labs. Through interviews, we found that students’ prior lab experiences were also overwhelmingly confirmatory, despite varying degrees of structure. We then used video of individual groups to explore the ways in which questionable research practices manifest through confirmatory expectations. We confirm previous work that students’ confirmatory expectations can lead them to engage in questionable research practices, but find that these behaviors occur despite instructional messaging about an alternative purpose. Our analyses also suggest that engagement in questionable research practices is more frequent than the previous results indicated through analysis of submitted lab notes. These results further illuminate issues with traditional labs, but suggest that the confirmatory goals, perhaps more so than high structure, are problematic.
This paper demonstrates the use of smartphones in an experiment of light absorption and light scattering. The LED display and camera of the smartphone are used as the light source and as the detector, respectively. The color wheel is used to choose the color of the light source to be shone through the sample for analysis. The detector directly measures the intensity of the light that passes through the sample to study light absorption according to the Beer–Lambert law. On the other hand, to investigate the light scattering, the detector orthogonally measures the intensity of the scattered light from the sample. The results of the light absorption correspond to the Beer–Lambert law. The scattered light from the sample is be measured by a smartphone. The experiment is easy to set up, without the need for any further expensive apparatus. We expect that this experiment will be useful for physics teachers to demonstrate light absorption and light scattering in the classroom or in a physics laboratory.
We propose the use of a smartphone based apparatus as a valuable tool for investigating the optical absorption of a material and to verify the exponential decay predicted by Beer’s law. The very simple experimental activities presented here, suitable for undergraduate students, allows one to measure the material transmittance including its dependence on the incident radiation wavelength.
Originally an empirical law, nowadays Malus’ law is seen as a key experiment to demonstrate the transverse nature of electromagnetic waves, as well as the intrinsic connection between optics and electromagnetism. In this work, a simple and inexpensive setup is proposed to quantitatively verify the nature of polarized light. A flat computer screen serves as a source of linear polarized light and a smartphone (possessing ambient light and orientation sensors) is used, thanks to its built-in sensors, to experiment with polarized light and verify Malus’ law.
In this paper we show how to obtain the Inverse-square law of the distance to
the light intensity emitted from a small source in a simple, fast and with good
precision way. With the aid of two smartphones, free apps and a ruler, one is
able to measure the distances between the devices listed (one as a source and
the other as a measuring light intensity) and the respective light intensities
measured by the probeware in the device. The ease of reproduction of the
proposed experiment and the penetration of the use of tablets and smartphones
among students and teachers, could make the proposed activity a good
alternative to the introduction of physical phenomena which exhibit the same
functional dependence, such as the Law of Newton's Universal Gravitation and
Coulomb's Law.
In this paper, we proposed a novel apparatus, which has very slim volume and can transfer light emitted from discrete LEDs into a uniform and ultra-collimated planar light source (UCPLS). This apparatus adopts the two-layer folded frame and two-stage CPC design so that thickness of the entire apparatus can be minimized; especially the feeder in the two-stage CPC design can greatly reduce the thickness of the CPC and make the light passing through the second-stage CPC become much more collimated. In addition, by side-by-side arrangement, a large-sized UCPLS can also be obtained. In our embodiment with an emitting area of the upper LGP of 280 mmX80 mm and a LED with optical flux of 8 lumens used as the light source, the performance according to the related simulation results shows as follows: angular FWHM of the resultant light emitted from the apparatus in the vertical and horizontal is 4.87 degrees and 24 degrees, respectively; spatial uniformity and total energy efficiency reach 84% and 69%, respectively; the average head-on luminance reaches up 5600 nit, yet this apparatus consumes just 60 mW. Furthermore, the results also demonstrate this design has potential to be applied to the product of 23 inches above while thickness of the entire apparatus is only 2.2 mm.
In this paper, radiometric ray tracing (R2T), based on phase-space formalism, is formulated.
The basic principles of Newtonian mechanics can be interpreted as a
system of rules defining a medley of modeling games. The common
objective of these games is to develop validated models of physical
phenomena. This is the starting point for a promising new approach to
physics instruction in which students are taught from the beginning that
in science ``modeling is the name of the game.'' The main idea is to
teach a system of explicit modeling principles and techniques, to
familiarize the students with a basic set of physical models, and to
give them plenty of practice in model building, model validation by
experiment, and model deployment to explain, to predict, and to describe
physical phenomena. Unfortunately, a complete implementation to this
approach will require a major overhaul of standard instructional
materials which is yet to be accomplished. This article lays down
physical, epistemological, historical, and pedagogical rationale for the
approach.
Light-emitting diodes (LEDs) come in many varieties and with a wide range of radiation patterns. We propose a general, simple but accurate analytic representation for the radiation pattern of the light emitted from an LED. To accurately render both the angular intensity distribution and the irradiance spatial pattern, a simple phenomenological model takes into account the emitting surfaces (chip, chip array, or phosphor surface), and the light redirected by both the reflecting cup and the encapsulating lens. Mathematically, the pattern is described as the sum of a maximum of two or three Gaussian or cosine-power functions. The resulting equation is widely applicable for any kind of LED of practical interest. We accurately model a wide variety of radiation patterns from several world-class manufacturers.
This article reviews a decade of research in transforming smartphones into smart measurement tools for science and engineering laboratories. High-precision sensors have been effectively utilized with specific mobile applications to measure physical parameters. Linear, rotational, and vibrational motions can be tracked and studied using built-in accelerometers, magnetometers, gyroscopes, proximity sensors, or ambient light sensors, depending on each experiment design. Water and sound waves were respectively captured for analysis by smartphone cameras and microphones. Various optics experiments were successfully demonstrated by replacing traditional lux meters with built-in ambient light sensors. These smartphone-based measurements have increasingly been incorporated into high school and university laboratories. Such modernized science and engineering experimentations also provide a ubiquitous learning environment during the pandemic period.
The Investigative Science Learning Environment approach replaces traditional teaching with active-learning methods that emulate scientific processes.
Smartphones are widely available and used extensively by students worldwide. These phones often come equipped with high-quality cameras that can be combined with basic optical elements to build a cost-effective DIY spectrometer. Here, we discuss a series of demonstrations and pedagogical exercises, accompanied by our DIY diffractive spectrometer that uses a free web platform for instant spectral analysis. Specifically, these demonstrations can be used to encourage hands-on and inquiry-based learning of wave optics, broadband versus discrete light emission, quantization, Heisenberg’s energy-time uncertainty relation, and the use of spectroscopy in day-to-day life. Hence, these simple tools can be readily deployed in high school classrooms to communicate the practices of science.
In this work, we present the design of a collimated backlight design that can be used for a liquid crystal display. The design is based on a hexagonal array of white light emitting diodes (LEDs) in combination with two arrays of lenses. Ray tracing simulations show a full width ‐ half maximum (FWHM) collimation angle of 2.8º with a uniformity of 73%. A prototype of this design has been fabricated and its performance has been analyzed. Compared to a standard backlight, the collimated backlight provides a 4.2 times better contrast ratio for a twisted nematic (TN) liquid crystal (LC) panel. In combination with a diffusor in front of the LC panel, the contrast ratio under a wide viewing angle is improved by a factor of 10 and the color shift is reduced by 79%.
A laboratory manual for high schools, colleges, and universities. The second edition contains more than 140 experiments and demonstrations presented in ten chapters: Introductory Experiments (30), Mechanics (11), Molecular Physics (11), Electricity and Magnetism (13), Optics and Atomic Physics (12), Condensed Matter Physics (11), Semiconductors (10), Applied Physics (11), Nobel Prize Experiments (10), and Student Projects (25). All the experiments are illustrated through the results of real measurements. New experiments developed by the author in 2007-2014 are added to this edition. © 2015 by World Scientific Publishing Co. Pte. Ltd. All rights reserved.
In recent years, smartphone sensors have been frequently used in educational demonstrations to improve students’ understanding of certain physical kinematic topics. In particular, the sensors on modern smartphones enable students to use their phones as physics mini-laboratories, and they have been used to analyze objects’ speeds and accelerations and to investigate the conservation of energy and magnetic field properties. As a particular example, one of the sensors on smartphones capable of being used to measure the speed and acceleration of light-emitting objects, and the value of g and spring constant, is the smartphone’s light sensor. In similar fashion, we now outline how a smartphone’s light sensor may be used to find the angular velocity, linear velocity, and centripetal acceleration of a light-emitting toy train moving on a circular track.
This study aims to measure Brewster’s angle of glass and acrylic brick with an easy-to-obtain mobile application (app) by changing the tungsten light source to a red laser. The popularization of the smartphone has inspired many to use its various built-in sensors to carry out general physics experiments. Many others have adopted both a laser and a light sensor to perform such measurements. In Refs. 10 and 11, the devices required specific software and are not widely available in physics laboratories. In this paper, we present a similar study, but one that has the advantage that it uses the ambient light sensor of the smartphone. In this work, a simple and inexpensive experimental setup is proposed to quantitatively measure Brewster’s angle.
The smartphone’s ambient light sensor has been used in the literature to study different physical phenomena. For instance, Malus’s law, which involves the polarized light, has been verified by using simultaneously the orientation and light sensors of a smartphone. The illuminance of point light sources has been characterized also using the light sensor of smartphones and tablets, demonstrating in this way the well-known inverse-square law of distance. Moreover, these kinds of illuminance measurements with the ambient light sensor have allowed the determination of the luminous efficiency of different quasi-point optical sources (incandescent and halogen lamps) as a function of the electric power supplied. Regarding mechanical systems, the inverse-square law of distance has also been used to investigate the speed and acceleration of a moving light source on an inclined plane or to study coupled and damped oscillations. In the present work, we go further in presenting a simple laboratory experiment using the smartphone’s ambient light sensor in order to characterize a non-point light source, a linear fluorescent tube in our case.
About twenty years ago, in the autumn of 1996, the first white light-emitting diodes (LEDs) were offered for sale. These then-new devices ushered in a new era in lighting by displacing lower-efficiency conventional light sources including Edison's venerable incandescent lamp as well as the Hg-discharge-based fluorescent lamp. We review the history of the conception, improvement, and commercialization of the white LED. Early models of white LEDs already exceeded the efficiency of low-wattage incandescent lamps, and extraordinary progress has been made during the last 20 years. The review also includes a discussion of advances in blue LED chips, device architecture, light extraction, and phosphors. Finally, we offer a brief outlook on opportunities provided by smart LED technology.
This work reports the use of a smartphone's ambient light sensor as a valuable tool to study and characterize the efficiency of an optical source. Here, we have measured both luminous efficacy and efficiency of several optical sources (incandescent bulb and halogen lamp) as a function of the electric power consumed and the distance to the optical detector. The illuminance of LEDs as a function of the distance to the optical detector is characterized for different wavelength emissions. Analysis of the results confirms an inverse-square law of the illuminance with the detector–source distance and shows good agreement with values obtained by classical experiments. This experience will trigger awareness in students in terms of sustainability, light propagation and efficiency of different optical sources.
Unrivaled in its coverage and unique in its hands-on approach, this practical guide to the design and construction of scientific apparatus, or laboratory instruments, is essential reading for every scientist and student of engineering, and physical, chemical, and biological sciences. Featured in this great new edition are features including the physical principles governing the operation of the mechanical, optical and electronic parts of an instrument, new sections on detectors, low-temperature measurements, high-pressure apparatus, and updated engineering specifications. 400 hand drawn figures and tables, have been added to this edition, which basically teaches scientists and engineers how to perform experiments.
Global computer modeling of display systems, based on Radiometric Ray Tracing (R2T), has been proposed, for determining radiometric (photometric) quantities in phase-space, including radiance (luminance) which represents phase-space density. Verification with experiment is also discussed.
The photometric modeling of LEDs as generalized Lambertian sources (GL-Sources) is discussed. Non-Lambertian LED sources, with axial symmetry, have important real-world applications in general lighting. In particular, so-called generalized Lambertian sources, following a cosine to the nth power distribution (n>=1), can be used to describe the luminous output profiles from solid-state lighting devices like LEDs. For such sources, the knowledge of total power (in Lumens [Lms]), the knowledge of the output angular characteristics, as well as source area, is sufficient information to determine all other critical photometric quantities such as: maximum radiant intensity (in Candelas [Cd = Lm/Sr]) and maximum luminance (in nits [nts = Cd/m2]), as well as illuminance (in lux [lx = Lm/m2]). In this paper, we analyze this approach to modeling LEDs in terms of its applicability to real sources.
— Understanding the display characteristics of OLEDs is not only of general interest but also of technological importance for expanding the application of OLEDs. The display characteristics of AMOLEDs were quantitatively evaluated and compared with LCD or CRT performance. The fast response time and high contrast ratio, which are attractive characteristics of OLEDs, were also retained under low temperature and bright ambient, respectively. Moreover the luminance and color barely changed with viewing angle at any gray-scale level. The optical design of OLED diodes is important for the emission characteristics, luminance, and color reproducibility.
In this paper, integrated lighting is discussed, including light sources, rough or relief surfaces such as diffusers and microprisms, as well as theoretical limits of ray tracing and photometry, and performance metrics of integrated lighting systems.
In this chapter we describe an interactive method of teaching, Investigative Science Learning Environment (ISLE), that helps students learn physics by engaging in proc-esses that mirror the activities of physicists when they construct and apply knowl-edge. These processes involve observing, finding patterns, building and testing ex-planations of the patterns, and using multiple representations to reason about physical phenomena. ISLE is a comprehensive learning system that provides a general phi-losophy and specific activities that can be used in "lectures" (interactive meetings where students construct and test ideas), recitations (where students learn to represent them in multiple ways while solving problems) and labs (where students learn to de-sign their own experiments to test hypotheses and solve practical problems). In ISLE, students are assessed for conceptual understanding, for problem-solving ability, and, most importantly, for their use of various scientific abilities. We have developed ac-tivities that help students acquire some of the abilities used by scientists in their work: experiment design, model building, use of multiple-representations, evaluation, etc. To determine the degree to which the students have acquired these abilities and to simultaneously provide feedback to the students, we have developed a set of ru-brics that can be used by instructors for grading and by the students for self assess-ment. In this chapter we also provide a theoretical basis for the ISLE structure (using brain and cognitive research), explain how this learning system addresses the needs of the 21 st century science education and workplace, and how it is different from other reformed curricula.
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