Economics of lighting systems

Codes and standards, energy efficiency, lighting controls, and plug loads all play into specifying lighting and lighting controls in nonresidential buildings.

09/24/2015


Learning objectives

  • Assess the various codes, standards, and guidelines that guide lighting design.
  • Outline the various lighting control systems.
  • Make use of cost analyses to determine the correct lighting and lighting controls.

Designing lighting systems has become progressively more complex. New energy codes require designers to deliver appropriate illumination with less energy; this also increases the sophistication of lighting control systems. In response to these changes, a variety of strategies and technologies have given the industry different methods of tackling these energy codes.

While many building clients are interested in seeing these systems integrated into their projects, they all have the same question: How much is it going to cost? Understanding the strengths of different approaches can help lighting designers specify a lighting system design that meets owner requirements while still meeting the necessary codes.

Table 1: This table outlines the lighting power density requirements by code/standard (building area method). All graphics courtesy: Harley Ellis DevereauxCodes and standards

A key driver to the increasing complexity of lighting systems are changes in energy codes. These codes have become stricter by lowering the amount of energy allowed for most building types and spaces (see Table 1). The predominant energy code impacting lighting energy allowances in the United States is ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings, of which different versions are adopted throughout the country (including the 2007, 2010, and 2013 versions). The U.S. Dept. of Energy’s State Energy Code Adoption Map provides details on the specific codes used in each state. Depending on the part of the country, the energy code in affect could vary by as much as 0.65 W/sq ft (family dining) to as little as 0.08 W/sq ft (museum). ASHRAE Standard 189.1: Standard for the Design of High-Performance Green Buildings also should be considered.

Optional energy initiatives also are playing a role in lighting system design. Programs such as U.S. Green Building Council’s LEED, Living Building Challenge, GreenGlobes, and International Living Future Institute’s Net Zero Energy Building Certification are putting tighter restrictions on designers to use even less energy than required by state-mandated codes. Government or municipality work often requires compliance with some of these (or other) optional standards. As such, it is important to research what optional standards may be applicable prior to performing any design. Knowing the impact of these standards early on is critical to designing a lighting system that meets or exceeds code requirements.

Table 2: The complexity of lighting controls must be carefully considered by the engineer when specifying lighting and lighting control systems.

While the energy allowed for lighting has decreased, the amount of recommended lux or footcandles for a task or space has hardly changed (see the Illuminating Engineering Society Handbook for recommendations). This leaves designers with two fundamental approaches for reducing energy while maintaining lighting levels:

1. Task-oriented lighting: Task surfaces are illuminated to the recommended lighting level for the task and function, and the surrounding spaces are illuminated at a lower level. This can be accomplished by having a general level of lighting and supplementing with task lights (desk lights, under-cabinet, wall-washing, etc.) or by having the overhead ambient source strategically located over the task areas. This approach can be cost-effective, as it can result in fewer ambient luminaires and targets the lighting where it is needed.

2. Efficient luminaires: Select luminaires that optimize the amount of lumens delivered to the work surface while minimizing the Watts used. Following this approach effectively means using LED or T5 fluorescent sources. While LED luminaires are often still more expensive than non-dimmable fluorescent luminaires, they become more economically viable when compared to dimmable fluorescent luminaires.

As energy requirements become more restrictive, designers are forced to use a combination of these two strategies to meet code. 


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