February 19, 2009
Want LEED credits for your lights? Plan early
By RANDY FISHER
The vast majority of the building industry agrees that sustainable design is the right thing to do, and the U.S. Green Building Council’s LEED certification process has become a main tool to certify buildings that meet stringent sustainability requirements.
Whether it’s due to environmental stewardship, government mandates, market drivers or peer pressure, owners are choosing more than ever to “go LEED.” But when the decision to go LEED comes late in the design process, it can bring on major design challenges for lighting designers and other consultants.
Lighting design is governed by codes, as is every other part of building design. Some of these codes regulate maximum lighting power density (LPD), energy used per square foot, light levels in specific spaces or even light trespass.
Some municipalities use the national energy standard, ASHRAE 90.1, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers. Other municipalities generate their own local energy codes.
These local codes also govern the industry and must be met when calculating energy usage for a space. In Seattle, the local energy code differs from ASHRAE 90.1, adding to code design challenges.
Catching up with codes
Proper lighting design attempts to incorporate the correct quantity of light fixtures to help reduce fixture costs and the LPD to save energy without sacrificing design goals. However, every few years the LPD allowances are lowered at different rates by both the national standards and local codes.
Since lighting technology remains about one step behind code requirements, just when it becomes simpler to design lighting solutions with existing lighting technology, the codes change to lower LPDs.
When a project goes LEED, a new set of challenges come into the equation.
Leslie Jonsson of CDi Mechanical Engineers explains: “In the earlier versions of LEED building certification, i.e. LEED 2.0 and LEED 2.1, the ability to reduce the LPD contributed to the reduction in total building energy usage, so that the reduction was not solely due to the mechanical systems.
“What we’re experiencing now in many cases with LEED 2.2, the LPD either meets or is slightly below the requirements, making it more challenging for the mechanical engineer to design to meet the minimum required 14 percent energy reduction. Concurrently, the mechanical system requirements are more stringent, as well, compounding the challenge.”
Limits of LEDs
To even attempt to achieve LEED, the prerequisite “minimum energy performance” must be met.
As mentioned above, the new LEED criteria require that the overall building energy be at least 14 percent below the new ASHRAE 90.1-2004 standards for new buildings. As part of the team, the lighting designer is asked to lower the LPDs as low as possible in order to help meet the 14 percent reduction.
Although sustainable lighting design at its most basic translates to using the lowest amount of wattage possible to provide light to a space, lower wattage does not necessarily translate to good lighting design. For example, the first-generation compact fluorescent lamp used less wattage than the incandescent lamp it was meant to replace, so it did save energy but had a poor color rendering and took five minutes to warm up to full brightness.
Today, it’s LEDs everywhere, they are touted as lighting’s panacea. But LEDs can provide poor color, fail to provide the listed long lamp life, or can be used for inappropriate lighting applications.
One LEED point is available for “light pollution reduction.”
This outdoor lighting credit has to do with the prevention of light trespass and light escaping into the night sky. Lighting designers must design for this credit from the beginning of the design.
Even though good lighting design always accounts for dark-sky issues, to earn this LEED point some sacrifices in aesthetically appealing lighting applications have to be made. For example, lighting trees or signs with uplights would have to be scrapped or redesigned.
In fact, the best approach to meet this credit is to have no uplighting at all. The light trespass portion requires multiple computer lighting calculations to prove that the project’s light fixtures do not allow light off the site.
A second credit related to electric lighting requires a lighting-control system that allows at least 90 percent of the building’s occupants to individually control lighting near their work spaces.
In order to gain this point, a lighting-control system with typically large upfront cost would need to be specified and have defined fixtures that are specifically coordinated with it. Attempting to implement a lighting-control system late in the design process requires the lighting designer to re-specify another fixture and/or ballast combination, and the electrical engineer to modify the light fixture circuiting.
Using available daylight is, of course, one of the most sustainable lighting solutions.
However, achieving the maximum potential light from daylight depends on the building’s orientation, the design and disposition of windows and other exterior openings of a building, and the placement of interior walls and furniture. For these reasons, designing for daylighting must be done early in concept design to achieve the full efficiency and benefits from natural light.
Of course, daylighting doesn’t address the fact that today’s society continues to function after dark due to electric lighting. The design of fixtures for nighttime requires careful lighting and energy planning in order to meet LEED requirements, even though daylighting has been employed in the facility.
Lamps and fixtures
Using lamps that generate more light, or lumens, per watt is a major component of sustainable lighting design.
In addition to the lamp itself, the fixture must be considered. Fixture manufacturers often list a model’s efficiency. However, without knowing the intended use of the fixture, its efficiency alone does not tell you the whole story.
If the fixture were simply a bare lamp, it would be listed as nearly 100 percent efficient. For example, a downlight may be listed as more efficient only because its lamp protrudes further out of its reflector compared with another fixture.
Professional lighting designers examine solutions such as high-quality reflectors to redirect light to the target area while balancing efficiency and glare reduction. Knowing that design will go LEED up front helps the designer to plan accordingly.
Designing to energy codes and LEED requirements helps us to attain environmentally friendly building design. But for all designers there needs to be a balance between the energy used and the overall feeling of the design.
Professional lighting designers believe that successful design not only saves energy but enhances the architecture and creates an environment that is comfortable and functional for the user. Making this happen while achieving LEED points can be done most efficiently when planning for LEED early in design saving redesign efforts as well as to time and money.
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