ENERGY CONSERVATION IN DWELLINGS-3 (Illumination)
“Total Lighting” is the traditional concept in illumination, which consumes more energy as whole space needs illumination to the required level. A combination of ‘Total Lighting’ and ‘Individual Lighting’ can greatly reduce the energy requirement. It means, non work places, such as corridors, wash rooms, halls etc. are at minimum level of illumination and work stations are illuminated to the required level.
Consumer should think of energy saving, while making choice of equipment, rather than initial cost. For example 5% reduction in equipment cost reduces overall cost by just 1%, whereas 5% reduction in energy cost shall lower the overall cost by 4%. That means cost reduction without lowering the quality or level of illumination. Efficiency of lighting apparatus plays an important role in energy conservation.
Replacement of incandescent lamps with fluorescent lamps, saves energy up to 80%. Sodium lamps have lowest energy consumption. Low pressure sodium lamp is most economical, but has limitations due to its colour. High pressure sodium lamp can be the best and economical alternative to fluorescent lamps. Now a days LEDs can replace practically any conventional luminary.
Efficiency also depends on various other factors e.g. size of room, colour of walls, height at which the luminaries are fixed, type of luminaries and control gear used. Energy distribution in an illumination system: 15% to 30% of wattage of the lamp is consumed by the control gear, the luminaries absorbs 20% to 50% of the light from the lamp, dark and dirty surfaces can absorb as much as 70% of the light coming from the luminaries.
Uniformity of illumination over a work space is governed by spacing-height ratio of the luminaries, which indicates the area that can be satisfactorily illuminated, when the luminaries are located at a certain height. Ideally this ratio varies between 1.25:1 and 1.5:1, which avoids excess illumination i.e. total illumination required and the lumens available from the luminaries should match.
“Utilisation Factor” of luminaries is the ratio of light reaching the working plane to light output of the lamp. Factors like, room size, absorption by walls and ceiling, obstruction due to partitions and huge machinery etc. play an important role in improvement of Utilisation Factor.
Replacement of lamps and periodical cleaning of luminaries play an important role. High pressure mercury lamp and fluorescent lamps develop black deposits at their extremities, near the end of their life. An anode ring is used to reduce this phenomenon. These lamps should be replaced in bulk after a certain period of burning, instead of haphazard replacement after the lamp failure. Comparatively, quantity of high and low pressure sodium lamps is less, hence bulk replacement is not justified.
Sun light is a cost free illumination source, which should be exploited to the fullest extent. Sunlight can be trapped through windows, skylights and north lights etc. Once the sunlight enters the space, either directly or diffused, it can be further exploited by encouraging reflections. In most part of India, bright sunlight is available for almost 250 to 300 days a year, which can be harnessed through innovative architecture. For example, in Hospitals, the patient rooms which need fresh air and sunlight are placed on the periphery of the building. On the other hand operation theatre is placed at the centre, where darkness is preferred.