Thesis (Ph. D.)--University of Hong Kong, 1980.

Anthropological research discusses the potential of light to act as a social agent, influence culture and substantially effect the ways that people interact. To enrich this scholarship with ethnographic engagement the following analysis applies and expands upon these concepts while discussing a database documentary about the moonlight towers of Austin, Texas. Moonlight towers are historic street lights dating from the late 19th century that are no longer necessary to light the city and yet they remain as fine engineered sentinels, shedding mercury vapor luminance over the city. This is a meditative inquiry into the types of agency light has in particular spaces referred to in this work as the ruminating concept of lightspace. As a concept, lightspace refers to the experience of light in space and is concerned with how light illuminates and shapes the everyday, tracing fissures between inclusion and exclusion. This work acknowledges the existence of lightspace in order to show there are ways that light shapes our experiences of which we are only partially aware. In the midst of this attunement to the experience of light are valid ideas about how people in Austin, Texas relate to space and to each other. The work of Henri Lefebvre is used as a point of departure to develop the concept of lightspace. In The Production of Space, Lefebvre arrives at the conclusion that the experience of geographical space is fundamentally social by making connections between perceived space and conceived space to create lived space of the imagination (1978: 70). In this philosophy, perceived space as constitutes our lived, everyday experience of space, while conceived space is a translation of perceived space using knowledge, signs, and codes, such as a map. Lived space then is our own unique, individual negotiation of perceived space using conceived space. This introduction to lightspace shows how connecting perceived and conceived lightspace in Austin reveals a lived experience of light in the imagination. / text

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

III-V nitride based light-emitting diodes (LEDs) have experienced rapid developments during past decade, proving their potential to substitute conventional incandescent bulbs and fluorescent lamps to fulfil energy-efficient and sustainable lighting needs. Tremendous endeavours have been made to improve the performance of LEDs, most of which focused on enhancing the internal and external quantum efficiencies. However, other optical properties of LEDs remain to be explored for a more flexible way of using LEDs in various applications. Therefore, this thesis proposes two nanostructuring strategies through the use of nanospheres to tailor the optical properties of LEDs. The nanostructured LEDs are demonstrated enable light emission with reduced divergence, or becomes polarized. The monolithic modifications are free of external optics and thus eliminate light loss, meanwhile providing manipulability of optical emission from LEDs. Firstly, close-packed indium-tin-oxide (ITO) micron-lenses with dimension of the order of wavelength have been integrated onto InGaN LEDs aiming at reducing the emission divergence. The sub-micron lens arrays are patterned by nanosphere lithography with silica nanosphere serving as an etch mask on ITO layer, leaving the semiconductor layer damage-free. An enhancement of up to 63.5% on optical output power from the lensed LED has been observed. The LED with 500 nm lenses exhibits a 26.8° reduction in emission divergence (full width at half maximum) compared with the bare LED. Three-dimensional finite-difference time-domain simulations performed for light extraction and emission characteristics is found to be consistent with the observed results. Secondly, polarization behavior of light emitted from InGaN LEDs propagating through a self-assembled polystyrene nanosphere opal film has been studied. Angular-resolved optical transmission of transverse electric (TE) and transverse magnetic (TM) polarized light has been measured. An integrated p/s ratio of 2.16 is observed at a detection angle of 70°, attributed to the suppression of TE mode at particular frequencies by the three-dimensional photonic crystal. Polarization is found to depend strongly on both the photonic bandgap of the opal and the angle of incidence. Theoretical calculations by transfer matrix method yield results consistent with the experimental data. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

It is observed that the power consumption of road lighting is increased with the length of trafficable road in Hong Kong. The energy used in road lighting is increasing, which means that the greenhouse gases (GHGs) emitted from power plant for generating electricity for road lighting is at the same time increasing. To compare the performance of light emitted diode (LED) road lighting with road lighting of other lamp sources, literature review, life cycle assessment (LCA) and technical assessment are adopted to give an overall comparison. This research focuses more on the environmental impacts of road lighting. LCA is adopted in order to give a comprehensive view on the environmental impact of road lighting. A total of 3 different lamp sources are compared: high pressure sodium (HPS) lamp, induction lamp and light emitted diode (LED) lamp. From the model result, it is found that due to the low power consumption and long life time, LED and induction lamp road lighting gives generally less environmental impact than HPS road lighting. As induction lamp has a longer life span than LED, the environmental impact of induction lamp road lighting is found slightly less than that of LED road lighting. Taking account the future development in LED technology, leading to longer life time, higher efficacy and lower production cost, LED road lighting is expected to be a replacement for road lighting in Hong Kong for the future. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Light pollution is a form of rapidly-growing and global-scale environmental degradation in which excessive outdoor lighting affects the natural environment, the ecosystem, and possibly even human health. Poorly designed outdoor lighting wastes energy and money, and robs the beautiful night sky. Effects of light pollution on the night sky can be evaluated by the skyglow caused by artificial lighting sources, through measurements of the night sky brightness (NSB). The Hong Kong Night Sky Brightness Monitoring Network (NSN) was established to monitor in detail the light pollution conditions in Hong Kong. Monitoring stations were set up throughout the city covering a wide range of urban and rural settings to continuously measure the variations of the NSB. Over 4.6 million zenith NSB measurements were collected from 18 distinct locations between May 2010 and March 2013. This huge dataset forms the backbone for studies of the temporal and geographical variations of this environmental parameter and its correlation with various natural and artificial factors. The average NSB in Hong Kong, excluding data affected by the Moon, was 16.8 mag 〖arcsec〗^(-2), or about 80 times brighter than the dark site standard established by the International Astronomical Union. The urban night sky was on average 15 times brighter than that in a rural location. NSB is not only highly depended on locality-specific distribution of outdoor artificial lighting sources, but is also associated with the amount of lighting switched on at particular times of night. The switch-off of lighting near midnight led to over twofold reduction in the observed skyglow flux in urban areas. The Moon was the major natural factor and could brighten a rural night sky as much as 6 mag 〖arcsec〗^(-2) at the zenith. On the other hand, in urban locations impacts of moonlight on NSB were barely detectable because it was overwhelmed by the artificial skyglow. The moonlight model of Krisciunas & Schaefer (1991) was tested against the observed night sky luminosity and was found to be about 30% accurate under cloudless and low luminosity conditions. Through comparing the NSB data with infrared sky measurements and visual cloud observations, it was concluded that the variation of cloud amount played a key role in determining the short-term and long-term observed fluctuations of NSB due to cloud’s back-scattering of upwelling city light to the ground, and clouds amplified light pollution more in urban than rural settings. Finally, the comparison between a night-time image taken from the International Space Station and ground-based NSB measurements reveals a strong correlation between the results taken from the two methods, suggesting good potential for the application of remote-sensing techniques on studying light pollution. This thesis shows the importance of continuing monitoring of light pollution, both by extending the operation of NSN, and complemented by examining high spatial resolution nocturnal remote-sensing data in the future. The above findings established the effects of artificial lighting on the night sky, and motivated the ways for light pollution reduction and developing dark sky protection policies in Hong Kong and beyond. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Abstract—A dependency of quantum efficiency of nn+pp+ silicon complementary metal–oxide–semiconductor integrated lightemitting devices on the current density through the active device areas is demonstrated. It was observed that an increase in current density from 1 6 10+2 to 2 2 10+4 A cm 2 through the active regions of silicon n+pp+ light-emitting diodes results in an increase in the external quantum efficiency from 1 6 10 7 to 5 8 10 6 (approximately two orders of magnitude). The light intensity correspondingly increase from 10 6 to 10 1 W cm 2 mA (approximately five orders of magnitude). In our study, the highest efficiency device operate in the p-n junction reverse bias avalanche mode and utilize current density increase by means of vertical and lateral electrical field confinement at a wedge-shaped n+ tip placed in a region of lower doping density and opposite highly conductive p+ regions.

What if Light was used to emphasis the Lightness of a Lightweight structure. In this project I set out to explorer the way in which we visually and emotionally experience “Lightweight”. I feel that car companies are beginning to see previous mistakes and engineer for a future in which physically lighter cars are requisite. This leads me to the question; how do we as designers communicate this in a positive way and sell a future efficient, lightweight lifestyle? I began the project by considering “What is Lightweight” especially in its visual and emotional forms. This thought process lead me to the use of abstract photography of light itself to help me to create a new lightweight BMW design language. The final result is a mixture of lightweight, twisting, structural forms that flow around the user to create a floating interior architecture. This will allow for, in a future autonomous world, the exposure of a fully lightweight transportation experience.

Pioneer 10 and 11 polarimetry maps of Jupiter, taken at a wide variety of phase angles, have been analyzed. Data were reduced in two colors for Jupiter's South Equatorial Belt (latitude -5 to -8 degrees) and scattering models were constructed. Variations in polarization from center to limb set constraints on the vertical structure of the atmosphere. The absolute polarization near the center of the disc constrained the single scattering polarization phase matrix of the scattering particles. After exploring several types of cloud models, it was found that a two cloud model with a haze in the upper atmosphere fits the data best. Several types of vertical structures were ruled out, including gas over a nonpolarizing Lambert surface, gas over a polarizing cloud deck, uniformly mixed gas with scattering particles (Reflecting Scattering Model), and models where the cloud tops diffusely mixed with gas as a function of altitude. Constraints have been set upon the polarimetric scattering properties of the haze and lower clouds. The haze particles are closely approximated by conservatively scattering spheres of index of refraction 1.5 and uniformly distributed sizes between 0.16 and 0.18 microns radius. A relationship exists between the required index of refraction for the haze particles and the mean size of the particles. It is possible that the particles are more broadly distributed in size, as this area was not extensively explored. The optical depth of the haze is between 0.125 and 0.250 at a wavelength of 0.44 microns, and lies near the 200 millibar pressure level. The upper cloud, which is thought to be made of ammonia crystals, must be at least optical depth 2, and could be semi-infinite. The polarization scattering properties of the clouds are distinctly different from the haze, indicating a compositional or size difference. The cloud particles have polarizing properties indicative of large (larger than 0.5 micron radius) particles. The upper cloud has been modelled to be near the 500 millibar level, but the pressure level for the best fitting model depends upon the chosen single scattering phase matrix. For more negatively polarizing cloud particles, the cloud would be located deeper in the atmosphere. The lowest cloud is more weakly constrained. Its scattering properties are set the same as the upper cloud, and it has been modelled as having semi-infinite optical depth. For the nominal scattering phase matrix, this cloud is located near the 2250 millibar pressure level. The constraints set on both the vertical structure and the particle scattering properties can be useful in the determination of Jupiter's solar flux deposition profile. Additionally, the location of the cloud and haze layers in Jupiter's atmosphere is important to the understanding of the heat balance of the planet, as well as to the understanding of the global dynamic of Jupiter's atmosphere.

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