Study of Illumination System in Surface Mining Projects and Development of Optimum Lighting Design Parameters

Abstract

Surface mining has been continuing and would continue to be an important industry in many countries. It is in fact the economic backbone of developing countries. Surface mines may cover several square kilometers of land, use large electric and diesel powered mobile type equipment, which runs almost continuously in all the three shifts. To maximize the production from such HEMM, large capacity haul trucks are used, which is common in surface mines. To ensure safe movement of men and machinery and for efficient working conditions, good efficient illumination needs to be provided during night hours. In mines a good lighting installation promotes good conditions of seeing. In surface mines where natural light is not available, especially during night hours, artificial light is provided for better seeing, which facilitates increased production, reduces worker’s fatigue, protects their health, eyes and nervous system, and reduces accidents. One major problem in surface mine lighting is continuous changing of task place, including roadways. Because of this reason it is difficult to provide any kind of long term permanent structure for illumination. Hence, the shifting of lighting installations at regular interval is very much necessary, so as to ensure required light level, as per the lighting standards specified by various regulatory bodies. Mine lighting has unique problems due to dark surrounding and low surface reflectance. To ensure safe movement of men and heavy earth moving machinery (HEMM) and for efficient working conditions, good efficient illumination needs to be provided during night hours and also during day time in case of adverse weather condition such as severe foggy atmosphere. The important aspect of lighting design is to provide sufficient illuminance on visual tasks. The luminance level, distribution of light (i.e. uniformity) and glare are the three important design parameters, which influence the visibility during night times. However, glare is not a major problem in surface mines, as it can be easily avoided by mounting the luminaries high enough to be out of the vision field. Further, glare can also be reduced through proper angle of orientation of the luminaire.ii In India, the Directorate General of Mines Safety (DGMS) recommends the standards of lighting at various parts of mine, in terms of minimum required illuminance level. However, these standards are only for the purpose of guidance. With proper layout, better visibility may be achieved even with lower illuminance level. In any lighting design uniformity ratio (UO) is very important, which decides the distribution of light in the area. Overall uniformity ratio should be considered for design purpose, due to typical prevailing work condition in mines. Though Indian mining regulations do not mention about uniformity ratio, International Commission on Illumination (CIE), Austria, stresses upon uniformity ratio as well. CIE also suggests for the average light level instead of minimum light level. Even the Bureau of Indian Standards (BIS) emphasizes on average illumination level and uniformity ratio for traffic roadway lighting. Scientific design of artificial lighting is very important to fulfill the lighting standards as prescribed by various regulatory bodies. The factors like type of luminaire, mounting height, pole interval, aiming angle etc., govern the design of lighting installation. While calculating illuminance level, one may wish to know its value at specific points or an average around the work place. Based on these, there are two methods of design techniques: point-by-point method and lumen method. The point-by-point method is most suitable to determine whether guidelines or regulations governing minimum illuminance or uniformity are being met. The luminous intensity distribution of a luminaire as supplied by the manufacturer is helpful in computing the light levels at any specified points on the work place. In this thesis, a mathematical model is formulated based on the two fundamental laws of lighting design, namely inverse square law and cosine law. The developed mathematical relationship is an added contribution to the field of lighting design. The computer programme is developed using MATLAB for performing the basic illuminance calculations. For validation of the developed programme, a telescopic light tower is fabricated, with varying tilt angle and light arm length. The arrangement is made for fixing different types of luminaries. For fixed installations, illuminance measurements are made in the field with varying design parameters, such as lamp mounting height, tilt angle and light arm length (overhang). The programme has been validated using a fabricated pole using 250W HPSV source and found to vary 2% to 5%.iii Cost is another very important factor to be considered in any project. In many projects, lighting is often the last item to be considered while estimating cost. Because of this low budgetary provision, the lighting installation may not result in congenial working environment. This may decrease human efficiency and increase accidental rate thus affecting the expected performance of the project. It is therefore essential to design a proper and cost effective lighting system in the early phase of the project for better working environment. In view of this, a suitable mathematical model has been formulated and a computer programme is developed using MATLAB to estimate the total annual cost of lighting system. To evolve optimum design parameters, a 9m width roadway is considered and horizontal illuminance level is measured at centre of the roadway for 150W HPSV source. The measurement is made by varying tilt angle from 0° to 30°, for three light arm lengths, such as 0m, 1m and 2m. The pole height is altered in five steps, such as 8m, 9m, 10m, 11m and 12m. The results of this study indicated that the luminaire is giving maximum lux level at 14° tilt angle with 0m arm length. Using the developed design model, the lighting system is designed for a hypothetical haul road of 1km length having 12m width (which is quite common in Indian surface mines), with six different types of luminaires (of different wattages), such as CFL, FTL, HPMV, MH, HPSV and LED. Lamp mounting heights are varied at five steps, namely 8m, 10m, 12m, 14m and 16 m. Tilt angle of luminaire is kept at 14° with 0m arm length. For all the above lighting systems annual energy consumption is calculated. Further, using cost model total annual cost for all the lighting systems is computed. This study revealed that 24W LED lamps at 8m pole height spaced at 17m intervals offer the most suitable lighting system based on optimal cost considerations. As a case study, an illumination survey is carried out in three surface mines (one limestone mine and two coal mines). The existing illuminance level at different places of mine is compared with the lighting standards specified by the DGMS. It was found that at many places illuminance level is well below DGMS guidelines. From these mines a part of lighting system was considered and it is redesigned for different types of sources, using optimum design parameters. The design has been made based on minimum illuminance levels and overall uniformity ratio. The study revealed that, properly designed lighting system can prove to be a cost effective solution for the mine management. Benefits accrued to the mines from the lighting design are highlighted. A few guidelines on optimum design parameters for surface mine illumination have been proposed in this thesis. The whole work has been divided into nine chapters. Chapter 1 explains the importance of illumination in surface mines. Chapter 2 deals with inter relationship between light and vision, properties of light, units of light, laws of Illumination, principles of illuminations, systems of surface mine lighting, sources of light and techniques employed for light measurement etc. Chapter 3 gives an insight on principle of haul road lighting and the parameters that hold key role in designing an illumination system, taking into account the cost parameters. Chapter 4 presents the development of computer program with MATLAB for designing illumination system and validation of developed computer program with the field data. Chapter 5 presents the cost evaluation of illumination system, formulation of cost model and development of computer program. Chapter 6 demonstrates the development of optimum lighting design parameters, such as tilt angle, light arm length, height of the pole and interval between the poles. Chapter 7 deals with the case study, wherein three mines are considered and their part of existing lighting system is redesigned with different types of sources based on optimum lighting design parameters. The energy consumption and the total annual cost are calculated for all the redesigned lighting systems. The results of the study indicates that the redesigned cost of lighting system has increased to 11.35%, 10.96% and 17%, respectively with that of existing lighting system to obtain the minimum of 0.5lux horizontal illuminance level with overall uniformity ratio of 0.3. Finally, a summarized results, discussion and conclusions as well as recommendations drawn thereof are elucidated through Chapters 8 and 9, respectively.