Many studies have revealed that proper use of sustainable technology in lighting, such as the use of daylighting controls and low energy lighting, has a strong potential for reducing the demand for energy in commercial and industrial buildings and there is potential for improving the energy efficiency of lighting systems throughout the world. A recent survey of several companies has found that 23% of all energy-saving opportunities could be achieved by improving the energy efficiency of lighting systems.
Enormous energy savings are possible using energy efficient equipment, effective controls, and proper selection of light source. Electric lighting design also strongly affects visual performance and visual comfort by aiming to maintain adequate and appropriate illumination while controlling reflection and glare. The problem of energy saving and the achievement of visual comfort conditions in the interior environment of a building is multidimensional.
Lighting controls help conserve energy and make a lighting system more flexible. The most common light control is the on/off switch, manual dimming, photosensors, occupancy sensors, clock switches or timers and centralized controls. Manual dimming controls allow occupants of a space to adjust the light output or illuminance. This can result in energy savings through reductions in input power, as well as reductions in peak power demand, and enhanced lighting flexibility. This type of technology is well suited for retrofit projects, where it is useful to minimize rewiring. Photosensors automatically adjust the light output of a lighting system based on detected illuminance.
Occupancy sensors turn lights on and off based on their detection of motion within a space. Some sensors can be also be used in conjunction with dimming controls to keep the lights from turning completely off when a space is unoccupied. These sensors can also be used to enhance the efficiency of centralized controls by switching off lights in unoccupied areas during normal working hours as well as afterhours.
Lighting controls can be grouped into two general categories: Centralized controls and local controls. Centralized controls are used in buildings where it is desirable to control large areas of the building on the same schedule. For example, in the morning the system can turn on lights a few minutes before the arrival of the employees. After the end of the working day the system can turn off lights again. During the day the lighting system can be adjusted in order to avoid peak demands (for example during noon at summer months). Localized controls are designed to affect only specific areas. There are various ways to control the lighting system for energy saving purpose. ‘On-Off” switch is the simplest and the most widely used form of controlling a lighting installation.
The initial investment for this set up is extremely low, but the resulting operational costs may be high. This does not provide the flexibility to control the lighting, where it is not required. Hence, a flexible lighting system has to be provided, which will offer switch-off or reduction in lighting level, when not needed. Grouping of light sources is also a way of lighting control systems for energy efficiency which can control light sources manually or by timer control. It can provide greater flexibility in lighting control.
Another modern method is usage of microprocessor/infrared controlled dimming or switching circuits. The lighting control can be obtained by using logic units located in the ceiling, which can take pre-programme commands and activate specified lighting circuits. Advanced lighting control system uses movement detectors or lighting sensors, to feed signals to the controllers.
Whenever the orientation of a building permits, day lighting can be used in combination with electric lighting. This should not introduce glare or a severe imbalance of brightness in visual environment. Additionally, sensor technology influences how well it detects occupants. Some sensors use infrared technology, some use ultrasonic technology, while others use a combination. There is a concern that some lamps have a shortened life if they are switched off and on frequently.
Programmed start ballasts offer the softest and smoothest lamp start and are intended to improve lamp life if a frequent on and off occurs. The use of daylight in buildings is an important and useful strategy in replacing the need for high level of conventional energy for inside illumination.
Study of the workspace
The lighting control system for corridors uses daylight and electric lighting jointly to provide task, background or general luminance. The design of control system depends upon sky condition and solar location. In order to establish the lighting controls, luminance measurements are needed for a minimum of three different seasons representing winter, rainy and summer.
Here, illuminated indoor environment is the Corridor of Electronic Science Department, University of Pune. The area is first studied for deciding the optimum illumination level. For this study, the corridor in which the light control system has to be installed is divided into four sections A, B, C and D as shown in figure 1.1.
Control System Design
As the cost of energy has continued to rise, increasing effort has gone into minimizing the energy consumption of lighting installation.
This effort has evolved along three major directions:
- The development of new energy efficient lighting equipment
- The utilization of improved lighting design practice
- The improvement in lighting control systems.
While saving energy is of great importance, there are some other associated benefits which should be considered. These are productivity and quality. However, it is quite difficult to quantify their influence. Lighting controls perform functions like on-off, time scheduling, dimming, and dimming due to presence of daylighting, lumen depreciation and demand control.
Lighting controls is an integral part of a lighting system. These controls must be responsive to the functional and aesthetic requirements placed upon it, and should perform these duties in an energy efficient manner. In general, there do not appear to be any general rules or guidelines that congenitally lead one to select specific controls. Energy savings due to daylight depends on climate conditions, building form and design and the activities within the building. In addition, this factor is directly linked with the operating schedule of the building.
Providing daylight in a building does not by itself lead to energy efficiency. Even a well daylit building may have a high level of lighting energy use if the lighting controls are inappropriate. Case studies have shown that in a conventionally daylit commercial building, the choice of control can make 30-40% difference to the resulting lighting use. Wireless protocol such as ZigBee technology is also widely used in various areas for its excellent performance in reliability, power consumption, flexibility and cost for lighting control. Lighting control could be performed by using fuzzy logic controller also. Using motion sensors, lamp groups are turned on when motion is detected. Thus, energy consumption was prevented by turning off the lamp groups when there is no motion.
In order to assess the energy efficiency of lighting installation especially in corridor of a building, a criterion for the installed electrical power is proposed which is broadly applicable and easy to use. The developed Lighting control system is basically based on energy efficiency of an indoor lighting installation for corridors which mainly includes use of daylight. The system is designed using 80S52 microcontroller. The block diagram of the developed control system is shown in figure 1.2.
As shown in figure 1.2, the lighting control system uses microcontroller 80S52/80C52 microcontroller. The system has two modes. In mode 1, the inputs from the LDRs are considered. The resistance of the LDR is varying according to the light intensity in the corridor. The signal conditioning circuit converts it into voltage which is given as an input to the ADC (Analog to digital Converter). The output of the ADC is given to the microcontroller and depending upon the light intensity, the tube lights will be turn ON or OFF.
In mode 2, different options of patterning of tube lights are given to user. User can select any one of them and then accordingly tube lights will be On or OFF. User can also change or design the patterning of luminaries by making a particular tube light on or off just by setting it to 1 to turn ON or 0 to off the tube light. There are total five options are given in the system. However, they can be increased by changing the programming of microcontroller. The system uses relays which actually turn on or off the tube lights.
After studying the illumination levels in all sections of the corridor (section A, B, C and D) and considering the comfort level of the occupants, it was found that minimum light intensity requirement in the corridor is about 60 lux. In section A, B, and D very less daylight reaches as these sections are interior part of the building. However, in section C sufficient day light is present because the main door of the department is open during the day time which is in section C. So, accordingly, the patterning of the luminaires in the corridor is designed.
Energy saving due to LED tubes
The eight existing light sources (T8 tube light of 40W) were replaced by 12W LED tube (which gives about 60 lux light intensity). Energy consumed by traditional T8 (40W) tube and by LED tube were compared. The calculations for both were done for 24 hours including day and night. Day is considered from 9am to 7pm (10hours) and night is considered from 7pm to 9am (14hours) in the next morning. The formula used for calculation is as follows:
According to table 1.2, due to the use of LED tube lights 70% energy is saved compared to traditional T8 (40W) tube light.
Energy saving due to Lighting Control System
Further, the calculations of energy consumption with developed lighting control system are done. Considering the day light, patterning of luminaries are designed. The calculations of energy consumed in summer season, winter season and rainy season is performed and then total energy consumed for one year is calculated. According to season the day light varies.
In summer season, sufficient day light is present throughout the day till 6pm. However, in winter season, because of cloudy climate less day light is present as compared to summer. In rainy season, assuming 56 days similar to winter season and 56 days similar to summer season and 20% days (that is 9 days) will be cloudy days. So the calculations for rainy season are different from summer and winter season. The chart of all the seasons with number of days and availability of daylight in a year is given in table 1.3.
As per table 1.2, the total energy consumption for one year without any lighting control system is 2803.2 units and using developed lighting control system is 439.185 units. So, total energy saving is about 84% per year by using developed lighting control system.
There are several instances in which lighting energy in the building has not been used efficiently. This could be because daylight is not efficiently integrated with the artificial lighting system, or in cases where integration does exist, energy savings using energy-efficient lighting technology have not been fully explored. The major issues of the owners for installing the lighting control system are initial investment, visual comfort of the people and aesthetic requirement of the building.
The main advantage of the developed lighting control system is that it can be fitted in existing wiring setup and thus saving the initial installation cost. The developed system is simple and cost effective as it is based on basic microcontroller. The daylight is integrated with the artificial light system which saves energy and LED tube light gives the aesthetic look to the building. LED tube light which is known as the “green light source”, saves energy up to 70%. In addition to it, LED lighting control system based on the microcontroller is the “Secondary energy saving” on the basis of LED light source which again saves energy and suggests many pattering options to the user.