| Summary: | Daylight was the main source of lighting in vernacular architecture, and building design accordingly responded to its strategic limitations. Needs for new types of buildings in conjunction with the great development of electric lamp led to the ascendancy of electric lighting. However, a return to the interest in natural lighting emerged with the energy crises in the 1970s. In order to meet the new requirements, new optical materials and technologies have been combined to produce innovative daylighting systems able to deliver daylight long distances into buildings. There is a need to maximize the utilization of daylight, to optimize the integration between davlighting and electric lighting systems so as to increase the potential application of daYlig~ing system. The development of the hybrid lighting systems (HLS) aims to satisfy these desires. / HLS seek to maximize the utilization of daylight by tracking sunrays, and in most cases they are concentrated to minimize the light guidance size, which eases the installation and in turn increases the potential application of HLS. Prior to delivery of daylight, electric lighting source is added to instantly top up any possible shortage of daylight. A control system works to regulate this process to minimize the energy consumption. The one output device for both sources used in the HLS made it possible to no longer need for two distinct lighting systems to be installed in one space. Investigations in this work have measured HLS performance in terms of light delivery, light quality, energy saving and economic performance. Potential applications of HLS in different buildings types and across a wide geographical region have been investigated. An overall evaluation of HLS has been carried out. Furthermore, methods to estimate illuminance data, where measured data is unavailable, have been developed to help investigating systems performance over different geographical locations. Illuminance data produced using the developed methods showed superiority over that produced using other available methods, with the additional advantages of simplicity and universal application. HLS performance and potential application are influenced by many variables including system characteristics, building types, and location features. The research showed that the most important variable is the concentration ratio of the light collector. This determines HLS ability to collect daylight, and thus its applicability in different geographical locations. It also stipulates light collector and guidance size, and thus HLS applicability in different building type, influences the delivered light quality, and thus occupants' perception of daylight, and influences HLS initial and running costs. Delivered light by HLS may not be perceived as daylight due to the absence of the outside view, the likely change in daylight colour because of the mixing with electric light, the fade awareness of the seasonal and diurnal changes in daylight colour and intensity because of the instant and continuous top up. The challenges of cost, light quality and integration in building design are the most serious barriers confronting HLS ability to penetrate the market and to be used widely. This work makes suggestions to overcome these problems.
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