Lorne Whitehead

Professor

Research Interests

Applied physics, especially novel geometrical approaches
Applied optics
Illuminating engineering and display technology

Relevant Degree Programs

 

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Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
An innovative daylighting system incorporating active light collection (2015)

The building industry recognizes the importance of incorporating daylighting into the illumination of buildings to improve both the energy performance of the building and the overall lighting quality. There are several well-known methods to increase the daylighting level in buildings, including windows and skylights. However, they are usually not capable of illuminating the core of the building, and may increase the energy usage of the building due to poor insulation. There are other systems designed for illuminating the core of buildings with daylighting, but they all have some limitations that have impeded widespread adoption.A daylighting system investigated in this PhD project offers a novel approach to illuminating the core of buildings. This system, so called the Two-Stage Core Sunlighting System, consists of active and passive optical elements that capture sunlight outside of the building and transfer it to the dark core. Active sunlight redirectors, mounted at the rooftop level edge of the building, track the sun throughout the day and redirect the sunlight towards building façades at a certain angle. Passive concentrator elements mounted on the façades of the building capture and concentrate the light and direct it into light guides. The sunlight is then distributed within the building via interior light guides that illuminate the building. The performance of the Two-Stage Core Sunlighting System was evaluated for five different cities. The energy savings calculations and the cost estimation showed that the Two-Stage Core Sunlighting System can provide a practical approach to daylighting a building without negatively impacting its overall energy performance. As a complement to the main research project, an analysis was carried out to determine whether performance improvements could be possible in the future. The analysis focused on modifications to the prismatic microstructured film, in particular the addition of reflective structures that may enhance the efficiency of the film by recapturing a portion of the energy that would otherwise be lost. Simulation results showed that such modifications do not substantially change the performance of the currently available microstructured films, but that they can improve the performance of a nanostructured film in future applications.

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Electro-optic diffraction grating employing electrophoresis, supercapacitance, and total internal reflection (2015)

Light beam steering is required in fields ranging from industrial laser drilling to telecommunications. Current methods for light beam steering to angles greater than 10° rely on mechanically moving parts, which results in expensive and difficult-to-maintain systems. An alternative method for light beam steering is presented that redirects a light beam to an angle of 33° without the need for moving parts. This is achieved by altering the reflectance of a surface by controlling the concentration of dye ions in a region adjacent to an optically transparent and electrically conductive thin film. Non-mechanical light deflection is achieved by altering the reflectance of a diffraction grating (an electro-optic method), an approach that creates new diffraction peaks that lie between those associated with the original grating spacing. This method for electro-optic diffraction is made practical by the supercapacitance exhibited at the interface between a layer of indium tin oxide (ITO) and a solution consisting of methylene blue dye ions dissolved in water. This interface was examined and measured to have a capacitance of 40 F/m² with a corresponding reversible change in the reflectance of this interface of greater than 50%.The capability of this method to reversibly deflect light was experimentally verified by fabricating test cells consisting of two glass plates, each coated with a thin film of ITO. A solution of methylene blue dye ions dissolved in water was sealed between the two plates. Electro-optic diffraction modulation was demonstrated by patterning one of the two ITO films into an interdigitated design, done via standard photolithography techniques for initial experimental verification, and via focused ion beam milling for sub-micron scale electrodes. An electrical potential difference was applied between the interdigitated ITO electrodes and the radiant flux of the newly created diffraction peaks was measured. The light distribution that reflected by means of total internal reflection from the ITO/solution interface was measured to reversibly shift 0.7% of the incident light to new diffraction peaks.This approach may be useful in applications where large diffractive deflection angles are required and alternate beam-steering methods are impractical.

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Light transmissive variable thermal insulator based on nonimaging optics with potential application in cold climate greenhouses. (2015)

Greenhouse structures have demonstrated success enhancing crop yields in farmlands, but the energy for thermal control and lighting make them impractical in cold weather locations because traditional greenhouse construction techniques result in a trade-off between light transmission and thermal insulation. The objective of the project described in this dissertation was to conceptualize, design and test a practical solution to the light transmission and thermal insulation trade-off challenge. The system that was developed is a variable light valve system that can be switched between two states – in one state the system acts as a sunlight transparent window and the other state the system acts as a highly thermally insulated ceiling capable of keeping the structure warm in cold weather conditions. Switching between the two states requires only a simple, low-cost rotation mechanism. The possibility of extending the hours of operation for the light valve system by adjusting the angular position of its light valve elements was also explored. The light valve system when in its highly thermally insulated state, demonstrated a thermal insulation value above 3.33 m²K/W and 70% light transmittance when in its light transmissive state. In order to achieve this thermal insulation value, air mass transfer losses through the light valve structure were reduced by the implementation of low pressure seal. The experimental devices used to test the light valve system demonstrated it can be constructed using inexpensive and readily available materials. The project described in this dissertation has successfully confirmed a practical solution to reduce the energy use for heating in cold climate greenhouses while maintaining appropriate sunlight transmittance through their structure. The light valve system may represent a practical alternative for cold climate greenhouse horticulture.

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Novel backlighting techniques for high dynamic range displays (2014)

High dynamic range (HDR) displays use an array of ultra-bright individually tunable light emitting diodes (LEDs) as a backlight for common liquid crystal displays (LCDs). Through local dimming of LEDs, this combination can show images with very bright highlights while maintaining very low luminance values in dark areas. Current HDR displays, however, have limitations associated with displaying images that have spatially uniform luminance levels: a periodic pattern arising from the underlying pattern of the LEDs behind the LCD is perceptible in the image.The effect of new point spread functions (PSF) on the uniformity and contrast of HDR displays was analyzed. A PSF shaped like a certain type of spline could theoretically create a uniform brightness backlight, as well as producing linear and quadratic gradients, while being capable of showing very high contrast. A practical way to produce such a PSF was used to build an experimental device that achieved a non-uniformity of only ±0.8%, while enabling a contrast ratio of 5:1 and 33:1 over distances of one and two unit cell spacings, respectively.The implementation of a third light modulator in HDR displays, in addition to the backlight LEDs and the front liquid crystal display (LCD) was studied: liquid crystal cells were combined with reflective polarizers to act as light valves, either transmitting or reflecting light. In theory, these reflective light modulators are supposed to decrease power consumption through light recycle effects.The power consumption of displays using the two discussed backlights was simulated. It was found that their power consumption is less than that of a common LCD by a factor of 2-5, but it is about 11 percentage points higher than for a standard HDR display. However, the image quality and contrast are improved compared to both state of the art displays. The advantages of the backlight with the new PSF may help to make HDR displays more useful and competitive in a wide range of applications requiring faithful luminance rendering such as discerning consumer markets, medical imaging, and motion picture editing.

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Strategies for promoting real-world connections in problem solving for introductory physics (2012)

It is well known that students’ beliefs about the nature of knowledge and learning in physics affect their motivation and learning in this subject. In this thesis I examine a course transformation that presented the entire course in terms of real-world circumstances and problems which was intended to promote students’ perception of the relevance of physics to the real world and to enable them to develop problem-solving skills for addressing complex real-world problems. By examining course-wide surveys I demonstrate that the intended improvement in students’ perception of the relevance of physics did not occur, suggesting that teaching physics in a real-world context is not, in itself, sufficient for improving students’ belief in the relevance of physics. Two interview studies reveal some of the features that students report are important in their perception of the relevance of physics to the real world. I use the theoretical framework of epistemological framing and resources to study students’ response to complex real-world problems that were intended to promote students’ use of real-world knowledge and enable development of expert-like problem-solving skills. I argue that students’ use of real-world knowledge within a physics context are opportunities for them to develop a more favorable attitude towards physics in general and develop a coding scheme for identifying these instances. This study demonstrates that students’ use of their real-world knowledge in physics is highly correlated with their framing of their activity as conceptual (rather than procedural) discussion. In addition, I demonstrate that the course’s structured problem solving method is not effective at promoting conceptual discussion at appropriate times during the problem-solving process.

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High dynamic range display andprojection systems (2009)

The human visual system can perceive five orders of magnitude of simultaneous dynamic range of luminance values. Recent advances in image capture and processing have made it possible to create video content at this level of dynamic range but conventional displays are unable show this rich content. Modern display and projection systems cannot deliver more than three or four orders of dynamic range and are usually limited to lower luminance values than those found in real world environments. This dissertation describes high dynamic range display and projection systems which resolve this bottleneck in the video pipeline and deliver luminance ranges to the limit of human perception. The design of these systems is based on the concept of dual modulation which combines several lower dynamic range image modulation components to achieve higher dynamic range. An overview of relevant perceptual mechanisms, viewer preference with respect to higher dynamic range images, and perceptual validation studies are discussed in addition to several implementation examples of dual modulation systems.

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Master's Student Supervision (2010 - 2018)
Electrically controlled frustration of total internal reflection on transparent superhydrophobic surfaces (2011)

Superhydrophobic surfaces are those that have a very low adhesion to water due to a combination of surface chemistry and physical roughness. This low adhesion surface offers the potential for enabling low energy optical contact between a liquid and solid surface. For the purposes of this study, optical contact occurs when the distance between the liquid and solid surface is less than the evanescent wave region of light that is undergoing total internal reflection.To develop an improved understanding of superhydrophobicity, a novel visualization technique was employed using neutrally buoyant immiscible liquids, which allowed liquid drops on the order of centimeters to be studied without distortion due to gravity. This allowed the visualization of wetting behaviors of liquids on different surface geometries, revealing the importance of overhanging structures to superhydrophobicity. A nanoporous, optically transparent film of polymethyl-methacrylate (PMMA) was fabricated via oxygen plasma etching with roughness features on the order of 100 nm. The surface was made superhydrophobic by spin-coating with Teflon® AF.A new technique was developed to modulate reflectivity by changing the optical properties at an interface by moving water to and from the interface. The technique electrically controls reflectance of visible light at a transparent superhydrophobic surface by frustration of total internal reflection and was demonstrated in an experimental device. The device consisted of a water drop positioned above a dual-scale superhydrophobic surface. Application of an electrical potential difference between the water and the surface caused it to undergo electrostatic deformation. This deformation would move the water into optical contact with the transparent superhydrophobic surface, thereby changing the optical properties and enabling the modulation of the surface reflection. Removing the electrical potential caused the water to return to its original curvature, separating it from the superhydrophobic surface. Such a device has potential applications as a low-power reflective display.The results presented in this work highlight the feasibility of this technique in practical devices, and suggest that further research is warranted.

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Electrolytic capacitive display (2011)

This thesis describes the novel use of an electrolytic capacitor to controllably modulate the optical properties of a surface. The electrically-controlled modulation is achieved using electrodes comprised of carbon nanofoam, a new allotrope of carbon that has an extremely high surface to volume ratio, resulting in a very high capacitance per unit volume which enables the material to attract a significant amount of electrostatic charge, an amount that is much greater than would be the case if the electrodes were not so highly porous.In the display described here, a diffusely reflective porous material, positioned above an interdigital array formed by two carbon nanofoam electrodes, was immersed in an electrolyte solution in which light-absorbing dye ions had been dissolved. When an electrical potential was applied across the electrodes, the capacitor charged and the dye ions were drawn into the pores of the electrodes and therefore drawn out of the bulk solution and porous material, causing the material to become reflective rather than colored. When the applied voltage was removed, the dye ions were able to diffuse out of the nanofoam and redistribute throughout the bulk solution and into the material, causing it to return to its original colored appearance. This effect was shown to be reproducible over many cycles and various experiments were conducted to develop a better understanding of the interaction of the dye ions with the carbon nanofoam electrodes and to understand how these interactions affect the time-course of the response.Potential applications of this technology include low power, high-contrast reflective image display devices, particularly in applications where the visual appearance of ink on paper is required. These so-called “electronic paper” displays are becoming more common in devices such as e-book readers, but the displays that are currently used in these devices are limited in terms of brightness and switching speed. The results of this research indicate that this approach using high capacitance porous electrodes may have application in high contrast reflective display devices.

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