International standards have specified lighting efficiency requirement in terms of lighting power density (LPD) to provide flexibility to the designer to meet the design as well as the efficiency requirements. LPD sets the maximum lighting power per unit of area of a building category or space function classification.
ECBC has set the minimum LPD requirement for whole building or for each space function to quantify the maximum allowed lighting power for a respective category to meet the lux level requirement prescribed in the National Building Code (NBC). Use of low Lighting Power Density (LPD) such as 0.45 in green buildings has resulted in significant energy savings in lighting. Such deployment has reduced air-conditioning load as well. In 2005-6, the LPD load which was in the range of 0.91.1 W/sq. ft and has come down over the years.
LED Lighting
Light Emitting Diode (LED) lighting provides more light for the same amount of electricity when compared to fluorescents, metal halides and halogens. Less heat is generated which also means less cooling energy requirements. LEDs reach full brightness instantly and can be turned off and on again quickly, allowing integration with controls like day lighting and occupancy sensors to further reduce the lighting energy consumption.
In the majority of applications it is important to choose LEDs with a high Colour Rendering
Index (‘CRI’, measured out of 100), which affects how accurately the human eye perceives
colour. They also tend to have long life, and less maintenance.
Occupancy detection
Occupancy detection uses sensors to identify when people are no longer using a space and switches-off (or turns-down) building systems, saving energy. This application is common for interior lighting, but it is also effective for heating, ventilation, air conditioning and exterior lighting.
There are a variety of different sensor types, suitable for a range of different distances. some are designed to detect movement; others detect ‘presence’ (when a person is present but not moving). Systems are even available that have one occupancy sensor per light, providing a high level of responsiveness and energy efficiency. ECBC specifies occupancy sensors to all office areas such as meeting and conference rooms, school classrooms, and storage spaces.
Daylight dimming
Daylight dimming (sometimes called ‘daylight harvesting’) uses sensors to identify when there is a good amount of natural daylight available and turns down lighting, saving energy. The sensors used are called ‘PE cells’ (photoelectric cells) - for external lighting it is normally just called ‘PE cell control’. A sensor can either be built into every light or shared between groups of lights but it is important to keep groups of lights small (because, for example, blinds might be adjusted). Internally, it provides the most benefit near facades, skylights and atria.
Flexible Lighting Control
Using only the lights when and where needed results in less energy use. Flexible lighting control systems provide the ability to link any individual light to any particular switch or sensor, without altering any physical connections. This allows the grouping of lights to be easily reconfigured for example when desks are rearranged in an office. It also enables separate lighting ‘scenes’ to be setup where a space is used for a number of different purposes. some control systems allow people to change the brightness of an individual light using their smartphone.
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