Energy Efficient Lighting Solutions

With the word GREEN - Environmental friendly living - hot topic today, many people wonder how they can play their part in this massive movement. One of the easiest ways to cut down energy drastically is by paying attention to Light Bill. Artificial lights on an average accounts for up to 20% of annual energy usage ! When we are able to cut down that amount, it can definitely make a difference to not only wallet but also to the environment. To get a realistic view of the cost of energy, consider that if every household replace old bulbs for energy efficient ones, the amount of greenhouse gases reduced would be equal to the gases emitted from approximately ten million vehicles !

Implementing this change can be as easy as switching from traditional light bulbs to Light Emitting Diodes (LEDs) / Compact Fluorescent Lamps (CFLs), and switching off the lights when they're not in use. Although CFLs / LEDs initially cost more than other bulbs, the savings they incur over time more than makes up for one-time expenditure. Maximizing natural daylight can also make it look larger and brighter, while saving on energy bills. While we don't often feel like these types of small changes really make an environmental difference, consider how much the difference would be increased if everyone tried to conserve energy in a similar manner.

The use of an energy-efficient lighting design not only provides significant lighting savings, but also can reduce the cooling requirements for a building. Engineers should use building energy modeling software to incorporate lighting system design and properly size the HVAC systems.

Building energy modeling software is widely used in the industry for a number of purposes including determining energy savings, HVAC design, or as a compliance path for U.S.Green Building Council LEED Certification. There are hundreds of different building energy modeling applications available, and each has its strengths and weaknesses. While there are many important factors in creating an accurate building energy model (building area, orientation, amount of glass, etc.), internal heat gains from people, lights, and equipment in the space contribute to the majority of the cooling load in many buildings. If engineers can develop more accurate energy models, HVAC systems can be optimally sized, resulting in energy-efficient systems with improved thermal comfort for building occupants and satisfied owners.

According to the study conducted, lighting is typically the largest source of waste heat, also known as heat gain, inside commercial buildings. Approximately 18% of the electricity generated is consumed by lighting loads, with another 5% being used to cool the waste heat generated by the lighting. Because lighting represents the largest portion of a commercial building's electricity consumption, it also presents a great opportunity for energy savings by using energy-efficient lighting systems and lighting controls. This applies to both existing and new buildings.

Interactive effects of lighting on heating and cooling

The type of lighting systems installed can have a large impact on the HVAC requirements. Reducing the energy used for lighting affects the heating and cooling that will be required. As more efficient lighting systems are installed in buildings, cooling loads will be reduced while heating loads can be expected to increase. On a new building designed with efficient lighting systems, the smaller cooling loads, in turn, allow for a building's cooling system to be sized smaller (and therefore less expensive to purchase and operate). On an existing building where lighting systems are upgraded to be more energy-efficient, the smaller cooling loads can allow for the existing cooling systems to serve future additional loads or to be replaced in the future with smaller units.

Most buildings are made up of several systems, including lighting, HVAC, and control systems. In order to design for optimal system performance, all building systems must be considered as a whole. When designing a new building or major renovation, interactions between the lighting and HVAC systems should be considered to ensure that equipment is sized properly for real-world conditions. Similarly, for lighting efficiency upgrades, engineers and owners alike should understand and be able to account for the potential heating and cooling load net impacts that various upgrades would create.

One of the inputs for an HVAC load calculation or building energy model is the lighting input power watts (W) or power density (W/sq ft). Table given below represents an example of how much this input power can be reduced by retrofitting existing inefficient T12 lighting systems in a building with various T8 efficient lighting system options. Using standard T8 systems results in a 26% energy savings compared to the baseline case, while high-performance T8 systems result in a 42% savings. Retrofitting T12 lighting fixtures with high-performance T8 lamps and ballasts, new lenses and mirrored specular reflectors can allow half of the lamps to be removed resulting in a 71% energy savings while still maintaining the same illuminance levels. Also, incorporating occupancy sensing and daylight dimming controls will provide additional energy savings. Note that this table does not account for the additional energy savings that may be realized by decreased cooling loads.

Dr. Prakash Barjatia
Director, MITSkills Center for
Lighting Technology, Pune, India.
Co-ordinator : LED Summit 2013
Governing Body Member, Indian Society of Lighting Engineers (ISLE)
Lead Assessor, NABL (ISO/IEC 17025)
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