How to reduce the Electrical Energy consumed by a Lighting System?

Last Updated 20 January 2017

Use of Electrical energy and its costs can be significantly reduced by installing energy efficient lighting system. Efficient building lighting systems use less energy than the systems in place in many of the houses, offices, schools, municipal buildings, stores, and plants. New energy-efficient lighting systems also provide better lighting quality and hence improve the working environment.

How to reduce the Electrical Energy consumed by a Lighting system?

Electrical energy consumed by a lighting system can be reduced either by reducing the lighting power or by reducing the time of use. Operating hours can be reduced by:

1.       Switching,

2.       Occupancy sensors,

3.       Scheduling controls, or

4.       Photocells.

How switching of a Lighting system helps the user?

Switching off the lighting system when not in use reduces the electricity bill and enhances the lamp life. For example, turning of fluorescent lights save energy and extends overall lamp life. Fluorescent lamps will run more hours if operated continuously, but they will last for many more years if they are turned off when not in use. Although the average rated life of fluorescent lamp is shortened by switching, calendar life is lengthened. The period, in hours or years, between the lamp changes is called Calendar life.

"For example, a standard F40 rapid-start lamp operated continuously result in a rated lamp life of 34,000 hours (calendar life of 34,000/8760 = 3.9 years). Turning off these lamps for 12 hours a day or because of approximately 2830 switching, the average rated life of the lamp is reduced to 30,000 hours, but the calendar life is extended to 6.8 years."

Occupancy Sensors reduces the Energy consumed:

Occupancy recognition is the strategy applied to intermittently occupied areas to automatically turn off the lights after the room is left unoccupied. The two principal technologies used for occupancy sensors are -

1)      Passive infra red (PIR) and,

2)       Ultrasonic techniques.

PIR sensors react to body heat and sense occupancy by detecting the difference in heat from a body and the background. Ultrasonic sensors are volumetric detectors and transmit waves above the range of human hearing, then measure the time for the waves to return. Ultrasonic units can detect persons behind obstructions. Sensitivity adjustments are also there to make an ultrasonic unit more or less sensitive to motion. Similarly delay adjustment sets the time the lights remain on when no occupancy is detected. Care should be taken as too short delay can reduce the lamp life and increase occupant complaints.

What is Scheduling Strategy?

Scheduling is a control strategy employed to activate, switch-off, or adjust lighting according to a pre-determined schedule. It is best suited for facilities where majority of activities happen at certain times. Time clocks are the easiest way to implement scheduling strategies and several types of time clocks are available in the market; viz. preset, electromechanical, electronic and astronomical. Astronomical time clocks are used to control outdoor lighting and can automatically adjust sunrise and sunset times. Programmable timer switches can switch lighting loads on-off several times during a day. They have the provision of removing selected days from the schedule and the same can be repeated each week.

Fig : A digital timer switch in circuit.

How Photocells helps in reducing Energy Consumption?

Photocells, made of cadmium-sulphide, are light activated switches used to turn off lights when daylight is adequate for safety and task performance. A delay feature prevents rapid operation during cloudy days.       

Thus, opportunities of energy saving through operational changes and better house-keeping must be identified as it the need of the hour. The short term and cost effective measures should be implemented immediately.