Lighting Design

Lighting is often considered the “low hanging fruit” of green building. The Energy Star Building Manual for Lighting reports that makes up 35% of commercial building energy use in the U.S. and consumes 18% of the country’s electricity.

Replacing inefficient lighting (or choosing more energy efficient lighting in a new construction) is relatively low cost with a high return. A lighting retrofit not only directly saves electricity, but also emits less heat, which reduces HVAC loads. If properly designed, lighting can also increase occupant productivity and safety.

Lighting Basics

When understanding lighting energy efficiency, it’s important to understand simple technological terms. Watts are the power put into the lighting system, and lumens are the lighting output. The lighting level is measured in foot-candles.

Lighting quality, on the other hand, is measured in terms of color, glare 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). Lighting ranges from a low temperature (200K), which looks reddish. As it gets warmer, the light seems white (5000K), and the highest temperatures appear blue (8000K). However, as the light becomes more white and blue, it is described as "cooler" in appearance (even though the temperatures are higher).

Lighting Energy Conservation Measures

One important component of energy efficient lighting design is to make sure the space is not overlit. The Illuminating Engineering Society (IES) provides guidance for appropriate lighting levels that will properly illuminate the space without wasting energy.

An important term when considering lighting energy efficiency is efficacy. Efficacy is measured in lumens per watt, and the higher it is, the more energy efficient the lighting is. However, higher efficacy does not necessitate higher foot-candles.

Types of Lighting and Lamps

The parts of a lighting system include the lamp, ballast, fixture and controls. The following are some of the types of lamps available:

Incandescent: These are the most popular type of lamp because they are the cheapest, but they are also the least efficient. Many incandescent lamps convert 90% of electricity to heat and only 10% to light.

Compact Fluorescent Lights: CFLs have become a popular alternative to incandescent lamps, because while they have longer lives and higher efficiencies, they are only slightly more expensive. T12 lamps, which are 1.5” in diameter, were the standard, but now smaller more efficient lamps such as T8 (1” dia.) and T5 (5/8” dia.) are becoming more popular.

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.

Induction: As the name suggest, these lamps product light by induction, which means that an electromagnetic field attracts plasma gas into a tube. These lamps, which have coloring similar to fluorescent lighting, last 8 times longer than fluorescent and 4 times longer than HID lamps.

Light Emitting Diodes: LEDs are very low power, high efficacy lamps with good color rendition and long lamp life. LEDs are becoming a more popular alternative as their prices continue to drop.

Daylighting: While this is not a type of lamp, daylighting is a type of lighting system that illuminates a space with sunlight rather than artificial light. Since natural light is used, daylighting can cut energy costs. However, daylighting systems must be properly designed such that the building does not become too hot or too cold and create higher HVAC loads. It must also be designed such that the space has enough lighting for occupant productivity.

With the exception of incandescents, all lamps requires a ballast, which controls 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.

Lighting Fixtures and Controls

A fixture is a lighting assembly that consists of the lamp, ballast, lens, reflectors and the housing. If the fixture is efficient, it will focus more light and produce more foot-candles.

Sensors and controls are also important components of lighting design. While traditional lighting uses a simple on-off switch control, more advanced systems will use occupancy sensors, timers, or dimmers to improve energy savings and increase occupant comfort and productivity. Photocells can sense the amount of daylight in the room and turn the artificial light on, dim or off accordingly.

Implications to LEED

Well-designed, energy efficient lighting can contribute to the following credits in the LEED for New Construction 2009 rating system:

• Sustainable Sites (SS) Credit 8, Light Pollution Reduction
• Energy and Atmosphere (EA) Prerequisite 2, Minimum Energy Performance
• EA Credit 1, Optimize Energy Performance
• Indoor Environmental Quality (IEQ) Credit 6.1, Controllability of Systems - Lighting
• IEQ Credit 8, Daylight and Views

As you can see, lighting can have an impact on many LEED credits, making lighting design an important component of registered projects. Lighting is considered one of the “low hanging fruit” in any green building project, because they make up 35% of a commercial building’s energy use, and changing light fixtures is a relatively easy fix.

Of course, designing for daylighting, controllability and other energy efficient or comfort strategies is more complicated, but can have a high payoff since it affects so many building components (and LEED points).

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