We are living in a world where energy, in a medium of fuel, is very much limited and the bad news is we have already consumed a bigger portion of it. With the help of new technologies and inventions day by day, the world is moving towards the renewable energy from non-renewable energy.Hence, we have to use the non-renewable energy intelligently to take the maximum output from this limited resource.

Nowadays by dint of media revolution and awareness, most of the people are familiar with the term “energy saving” or “electricity saving” but they don’t have the proper knowledge and skill about it. One of the reasons is most of them are a non-technical person or being in another technical field which is not relevant to the energy saving concept. Whenever it comes to the question of energy saving our subconscious mind tells “it is a big issue and I have no role on it”, “Energy savings can only be done on large scale industries.”

This is totally a misconception that only in large scale industries where big machinery, boiler, chillers are used can save energy. We can save energy too through lighting system that we are using at our home, office, multi-storied building, Market and of course in industries just by applying some simple technique within our reach. But if we want to use the least amount of energy to get the maximum amount of output we need expert opinion and guideline.

How much energy can be saved through the lighting systems?

Lighting systems normally take more than 20 percent of the electrical energy consumed in commercial buildings.Lighting systems not only consume power to generate light but also generate heat as a by-product, in air-conditioned buildings this added heat by lighting has to be removed by the building cooling systems. Therefore, lighting systems need to be carefully designed to achieve the desired illumination level while using the minimum amount of energy.

Main steps in Energy savings from lighting systems can be achieved as follows:

  1. Optimizing lighting levels by reducing the number of lights
  2. Improving the efficiency of lighting systems
  3. Using external controls in lighting systems
  4. Using daylighting (using natural light).

 

Terms we need to understand

One of the most common measures of light output is the lumen, which is the SI unit for luminous flux. Lumen is the quantity of light emitted by a source or the quantity of light received by a surface. Light sources are labeled with an output rating in lumens. Typical values of luminous flux emitted by some common sources of light are given below

 

Table-1: Luminous Flux Emitted by Common Light Sources

Type of Lamp Lamp wattage Lumens
Torch lamp 03 W 30
Incandescent lamp 75 W 950
Compact fluorescent lamp 15 W 810
Fluorescent lamp 36 W 2,400
High-pressure sodium lamp 100 W 10,500
Low-pressure sodium lamp 131 W 26,000

 

In this table, it is very easy to understand that compact fluorescent lamp and fluorescent lamp, commonly known as tube light, are more energy efficient than that of incandescent considering the lumens value.

Other two factors those need to be taken into account are:

Luminous efficacy: Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power. This ratio indicates the efficiency of a lamp in converting electrical power into light. The better the luminous efficacy is the lower the power consumption is. Just for extra information, Edison’s first electric filament lamp had an efficacy of 1.4 lm/W (The units of efficacy are lm/W.).

The Color Rendering Index (CRI): CRI is an indication of the ability of a light source to accurately show colors. Natural light will have a CRI of 100. Electric filament lamps produce a continuous spectrum with all colors present and, therefore, they have a CRI of 100. Normally, CRI below 80 is considered poor color rendering while CRI above 80 is considered good.

Table 2: Luminous efficacy and Color Rendering Index comparison

Lamp type Efficacy (lm/W) Color rendering index (CRI)
Incandescent 10–15 100
Tungsten Halogen 13–25 100
Compact fluorescent 50–60 75-83
Fluorescent lube 69–100 80–95
Metal halide 85–120 65–80
High-pressure sodium 80–140 25
Low-pressure sodium 150–200 0

 

Keeping others complex factors aside any non-technical person can choose the best-suited light for him just by comparing these two factors.

 

Recommended Lighting Levels

Required lighting level depends on the type of space, jobs performed in the space, and other visual requirements.For some common building spaces, a general guideline for lighting level can be considered as the following table

Recommended Lighting Levels for some common building spaces

Type of area Recommended design value (lux)
General offices, conference rooms, computer workstations 500
School classrooms 300
Shops, departmental stores 500
Supermarkets 750
Hospitals 300
Lobbies, corridors 150
Hotel rooms 100-300
Car parking areas 15
Car parking entrance 100

 

Due to lack of technical knowledge, generally, people waste energy by over-lighting those common areas then recommended level. With the help of this guideline, unnecessary wastage of electricity due to excessive lighting levels can be reduced.

 

Energy Saving Measures

Energy can be saved by taking some measures through lighting systems. These energy saving measures can be segregated into three types.

  1. General saving type
  2. Proper lamp selection
  3. Saving through the control

General saving type

Reducing lighting level as per recommended level (according to the table provided) is the most common and simple step to save energy as higher lighting levels lead to higher lighting energy consumption.  For new installations, this can be achieved through good lighting design in the first place. For existing lighting system it is very hard to adjust at the very first time but with time it will be adopted by the user. The process used for reducing light from an existing system is called de-lighting, which is elaborately described below.

De-lamping is another simple idea by removing one or more lamps from a fixture (that has more than one lamp) in areas where the lighting level higher than required. Without having sound knowledge just by guessing and simply removing lamps could sometimes give an impression of the building is poorly maintained.

Using task light, the lighting system which only is used during the task performed in a particular area is another way to save electricity. In many building spaces, general lighting is provided uniformly at a higher level so that the required lighting level can be achieved on the work surfaces. This unnecessary level of lighting can be reduced just by introducing task lighting on that specific area where the extra light needed.

Proper lamp selection

Low efficacy incandescent lamps have only about10 to 15 lm/W so they are not energy efficient. They can be easily replaced with compact fluorescent lamps (CFL), which have a much higher efficiency. In general, CFL lamps consume only about 20 to 25 percent of the power consumed by incandescent lamps to produce the same amount of light.

Linear fluorescent lamps are one of the most common types of lamps used for general lighting in offices, corridors, car parks etc.  Linear fluorescent lamps have evolved over time from old T12 to T8 and later to T5 lamps. (The tubes are classified by a T number, which refers to the tube diameter in 1/8 of an inch. So T12 refers to 12  × 1/8  =  1.5 inch (38 mm) tubes.) T8 tubes have more efficiency (90 lm/W) than T12 tubes (efficacy 69 lm/W) and the good thing is they are exact same length so they are easily replaceable. Though efficiency ( 100 lm/W) of T5 tubes are higher than T12 and T8, due to the shorter tube length of T5 lamps, they cannot be directly fitted to existing  T12 or T8 fixtures. Therefore, use of T5 lamps should normally be considered for new installations rather than for retrofitting existing fixtures.

Metal halide lamps, mercury vapor lamps, and sodium lamps are called high-intensity discharge (HID) lamps. They are able to provide better efficacy and longer life than fluorescent lamps. These types of lighting applicable in warehouses, factories, large stores, and sports facilities. High-Pressure Sodium lamps should be used instead of mercury vapor lamps as they have a higher efficacy. High-pressure sodium lamps are also able to produce a fuller spectrum of light, which can help improve nighttime visibility.

Nowadays LED (Light-emitting diode) tubes are getting popular as lifespan and efficacy of LED is much longer and higher than linear fluorescent lamps and they are easily replaceable to any T12 or T8 tube fixture. Initial costing is higher than linear fluorescent lamps. Most LEDs do not emit light in all directions.

 

Saving through the control system

A lighting control system is an automatic system which allows you to have control of the lights in a space depending on schedule time, space occupancy and light demand. There are various types of lighting control systems available to save energy. Earlier automatic lighting control system was popular in industries, offices and shopping malls but with the technical revolution and availability of high-speed internet, these systems are getting common for home use.

Timer schedules circuits: Simple timers can be used to switch on and off all or some lighting circuits at predetermined times based on occupancy schedules. Provision for manual override can be incorporated into the controls so that occupants can extend the operating hours of lighting circuits based on individual requirements.

Occupancy sensor: Occupancy sensors can also be used to switch on lighting when space is occupied and switch off the lighting after a preset time delay when space is not occupied. Typical applications for occupancy sensors are in toilets, car parks, meeting rooms, storage areas, and common corridors.

Light sensor: Making adequate use of natural light is another way to reduce a building’s energy load. Exterior and interior areas of buildings, which are exposed to natural light, can have light sensors to switch off or provide dim artificial lighting when sufficient natural light is available. The daylight controls can be the open-loop type where the sensor detects available daylight or the closed-loop type where the sensor detects available light at a work space.

In this article, we have touched only the surface of the lighting system and how we can save energy through the lighting system. By reading this article you can take initiative to do some minor changes in your lighting system but a vigorous change in the lighting system to save sufficient amount of energy without proper expertise may not be as beneficent as your expected.

 

Benchmark Solutions Energy Audit  team has AEE (Association of Energy Engineers) accredited Certified Energy Auditors (CEB) who are capable of review your lighting system and controls as well as your overall energy management system and make specific recommendations regarding viable lighting efficiency improvements. These improvements will help to run your system safely, reliably and in cost-efficient way.

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