Advice provided by: David M. Pratt, P.E., CEM, LEED AP, MWH

Share

According to the Energy Star Building Manual for Lighting, lighting accounts for approximately 35% of the total energy used in a typical commercial building in the United States and 18% of all electricity generated in the U.S.

Lighting can also affect the energy usage of other building systems such as HVAC due to its heat output. Lighting upgrades are often the first Energy Conservation Measures (ECMs) that are implemented in a building due to their relatively low cost and high return on investment (ROI), and are often considered the “low hanging fruit” in an energy audit. Additionally, the quality of lighting can affect employee productivity and reduce risk (safety), which can overshadow ROI from pure energy savings. With careful consideration, lighting upgrades and retrofits can have an enormous impact on a company’s bottom line.

Before we get into discussing the various lighting technologies available, let’s discuss some basic lighting fundamentals. The power input to any lighting system is measured in watts, while the output is measure in lumens. However, the actual lighting level received at the workplane is measured in foot-candles.

There is also a difference between the quantity of light delivered in lumens or foot-candles, and the quality of light. Lighting quality has a powerful effect on the mood of building occupants. Light quality can be described in terms of its glare, color and temperature. The Color Rendering Index (CRI) is “an evaluation of how colors appear under a given light source” according to the Energy Management Handbook (7th Ed.) and has a scale of 0-100, higher being better color rendering. The Coordinated Color Temperature (CCT) “describes the color of the light source,” and is measured in Kelvins. A lower temperature (200K) appears reddish, and as the temperatures rise, colors appear white (5000K) and then blue (8000K). However a higher temperature light is described as “cooler”, as it gets more white and blue.

Lighting Energy Conservation Measures

The first step is any lighting ECM is to review the existing lighting design and determine if the space is over illuminated. Most buildings are over illuminated, and much energy can be saved by simply reducing the lighting to the levels recommended by the Illuminating Engineering Society (IES).

When describing lighting efficiency, engineers use a term called Efficacy. Efficacy is measured in lumens per watt. The higher the efficacy, the more energy efficient the lighting system is. Keep in mind however that light received at the work plane is measured in foot-candles, and higher lumens does not always equal higher foot-candles.

Types of Lighting and Lamps

There are many components that go into a lighting system, including the lamp, ballast, fixture and controls. First we will discuss lamps. The lamp most people are familiar with is the “Edison” lamp, or incandescent lamp. This type of lamp is the least efficient, but is popular because it has a low initial cost and has been around for ages. Compact Fluorescent Lamps (CFLs) have a much higher efficacy and longer life than an incandescent lamp, which allow it to have a lower overall life cycle cost which should make up for the slightly higher initial cost. Fluorescent lights are very common in commercial buildings. T12 lamps, which are 1.5” in diameter, used to be the standard and are now being replaced by smaller more efficient lamps such as T8 (1” dia.) and T5 (5/8” dia.). High Intensity Discharge (HID) lamps are similar to fluorescent lamps but can have longer lifespans and higher efficacies. HID lamps include Metal Halide, Mercury Vapor, High Pressure Sodium and Low Pressure Sodium. HID lamps are typically designed for outdoor and industrial use but some can be used in an office environment. High and Low Pressure Sodium Lamps are great for an outdoor or industrial environment where color rendition is not a big factor. They have very high efficacies and long lifespans, but would not be a good choice for an indoor office environment due to the low CRI and CCT. Mercury Vapor lamps were some of the first HID lamps available, and have mostly been replaced by other technologies such as Metal Halide which has a higher efficacy, CRI and CCT.

Induction lamps have a very long life span, up to 8 times longer than a fluorescent lamp and 4 times longer than an HID lamp according to the Energy Management Handbook (7th Ed.). This is because induction lamps have no electrodes that wear out. Instead, these lamps produce light by means of induction, which is a process that uses an electromagnetic field to induce a plasma gas discharge into a tube. The color rendition is similar to fluorescent lamps.

LED lamps appear to be the wave of the future. They are very low power, high efficacy lamps with good color rendition and long lamp life. LED lamps are already widely used in applications such as exit signs, traffic lights, and outdoor lighting. LED “fluorescent replacement” lamps are now readily available for use in the commercial office space. The costs are coming down so much that LED lamps will soon be a very competitive alternative to efficient fluorescent lamps, if they aren’t already.

As I stated previously, lamps are only one component in a lighting system. All lamps with the exception of incandescent lamps require a ballast. Ballasts control the power that is supplied to the lamps and have what is known as a ‘ballast factor,’ which controls the output of the light of the lamp. A ballast with a higher ‘ballast factor’ will put out more light, and in turn consume more energy. Ballasts for fluorescent lamps are typically either magnetic or electronic. Magnetic ballasts used to be the standard, and are slowly being replaced by newer, more efficient (up to 30% more efficient) electronic ballasts. Electronic ballasts are more efficient because they convert the standard input frequency of 60 Hz to a much higher frequency, which will produce the same amount of light while consuming much less energy.

Lighting Fixtures and Controls

A fixture is a lighting assembly that consists of the lamp, ballast, some type of lens and reflectors and the housing. As I stated above, more lumens does not necessarily mean higher foot-candles at the work space. This is due to the fixture efficiency. The more efficient the fixture is at focusing the light in the intended direction, the more foot-candles will be produced at the work surface.

Sensors and controls play a large part in the overall energy usage of a lighting system. Basic controls for a lighting system are the on/off switch. However, as much as the concept of turning off the lights when one leaves a room has been pushed on the general public since child hood; people still leave the lights on. So an occupancy sensor will help take the guesswork out of the equation and turn the lights on or off when a room is occupied. For outdoor applications, photocells can do the same thing and turn the lights on when it gets dark, and vice versa. Photocells can also be combined with a dimmable electronic ballast to dim the lights when daylight can be used in the space.

Daylighting is a technique to use the natural light of the sun to light the interior of buildings. I won’t go into much detail on this topic here, but there are three commonly used daylighting techniques including skylights, perimeter daylighting, and building core daylighting. The more natural sunlight that can be used, the less electricity needs to be generated. Keep in mind that if done improperly, daylighting can introduce too much glare and can cause additional cooling loads in the building. Proper consideration should be given to all building systems when designing any type of lighting system.

Implications to LEED

Lighting can affect a LEED project in many different ways. Obviously a lighting system that uses less energy will help earn LEED points in the EA Credit 1 (Optimize Energy Performance). A good lighting design will also help earn points in SS Credit 8 (Light Pollution Reduction), IEQ Credit 6.1 (Controllability of Systems, Lighting), and IEQ Credits 8.1 and 8.2 (Daylight & Views, respectively). There may even be an Innovation in Design credit for truly outstanding lighting designs.

In summary, lighting can affect green buildings in many ways, from energy usage to the productivity and mood of building occupants. As mentioned above, lighting accounts for almost 35% of all energy usage in commercial buildings, and are often considered the “low hanging fruit” for any energy audit. There are numerous components in a lighting system including the lamp, ballast and fixture, and should all be considered when designing a new or retrofitting an old lighting system. Efficacy, color, temperature and life span are all important factors in considering a new lighting technology. Lighting design can also impact a LEED project in many ways, accounting for many points in up to 5 different categories. As with any technology, it’s imperative that the lighting design takes all of the building systems into consideration in a holistic, integrated process.

Related Advice:

• T12 Lighting vs. T8 Lighting: How Much Can I Save?



• Commercial LED Lighting: Converting to LED from T8



• LED Lighting and Section 179d Tax Deductions: Everything You Need to Know



• Lighting Fixtures in LEED Certified Buildings: Is Energy Star Approval Necessary?