Sustainable lighting choices under LEED indoor environmental quality guidelines

Lighting insights

• Lighting fixture manufacturers are adapting to support LEED compliance by prominently featuring luminance data and UGR ratings on specification sheets.
• Strategies outlined include glare control, color rendering, lighting control and surface reflectivity.

Like energy codes, U.S. Green Building Council LEED (Leadership in Energy and Environmental Design) credits develop into more challenging targets as each version rolls out. While LEED certification is not a new concept, its impact within all aspects of a potential design may be unfamiliar to those who have not dealt with it directly. Indoor environmental quality (IEQ) requirements specifically are outlined in LEED v4.1: Interior Lighting.

For lighting designers and specifiers, it is important to first understand if LEED is a target for your project. This may be an owner directive, proposed design target or energy code compliance path, especially as some jurisdictions are directing projects to meet LEED certification requirements for code compliance.

For example, Denver’s latest energy code amendments include an optional pathway to achieve LEED Platinum certification. When pursuing LEED certification, it is important to with the project team’s sustainability consultant to confirm which credits will be targeted, and to start discussing how they may impact the lighting design early in the schematic design phase. It is much more difficult to backtrack and update a completed design to meet LEED compliance.

Under the IEQ section for new construction, there are two possible points for interior lighting. The intent of this section is to promote occupants’ productivity, comfort and well-being by providing high-quality lighting. To fulfill requirements, projects must meet one strategy for one point and three strategies total for two points. The strategies outlined are glare control, color rendering, lighting control and surface reflectivity.

Figure 1: Visual representation of glare as experienced in a typical office setting. One of LEED’s targets is to reduce the discomfort experienced by an occupant due to glare. Courtesy: Smith Seckman Reid Inc.

Understanding IEQ definitions

Below are compiled definitions to assist in breaking down the strategies noted above.

• Color fidelity index: Qualitative measurement of a light source’s ability to accurately represent 99 specific colors in comparison to the sun. (See ANSI/IES TM-30 for additional details.)

• Color rendering index (CRI): Qualitative measurement of a light source’s ability to accurately represent eight specific colors in comparison to the sun.

• Gamut index: Qualitative measurement of how intense or saturated colors appear under a specific light source.

• Glare: The disturbance or reduction of eyesight as caused by high luminance, specifically in lighting.

• Luminaire: A complete electric light unit, also referred to as light fixture.

• Luminance: The intensity of light emitted from a source, measured in candela per square meter (cd/m²).

• Nadir: The vertical line projecting downward from the center of the luminaire.

• Unified glare rating (UGR): An industry development method that puts a measurable value to glare. It considers the background luminance, luminance of the luminaire within the observer’s line of sight, the angle of the luminous part of the luminaire at the observer’s eye and the displacement of luminaire from line of sight. UGR may be calculated for an individual fixture (while making assumptions) or a complete design when modeled in a lighting calculation software.

Breaking down the LEED credit for lighting

The two approaches noted in the official LEED language for glare control may seem daunting and sound like a calculator will be necessary, but that is not always the case. For either option, the fixture manufacturers have already done the work and will be able to provide the individual fixture information.

Luminance data of a luminaire can be found in the Illuminating Engineering Society (IES) fixture file or will be provided by the manufacturer on the specification sheet. An IES file contains the photometric data of a given fixture. These files are typically intended to be used in a lighting calculation software and will be needed when calculating the UGR of a design. The main factors that impact the luminance of a fixture are the fixture output in lumens and the fixture’s aperture size. As a lumen package increases for a given fixture, the luminance also increases. When comparing aperture sizes, a two-by-two troffer compared to a two-by-four troffer of the same make, model and lumen output will likely have a significantly higher luminance.

If meeting the luminance requirement is not a possible path, the alternate option for glare control is meeting a design’s UGR of less than 19. A design’s UGR number corresponds to the occupant’s discomfort from the amount of glare experienced. Typical ratings fall within the range of 10-30. The higher the UGR numbers, the more glare is being experienced, which leads to discomfort.

Individual fixtures have UGR data as provided by the manufacturer, but the LEED strategy requires projects to use software modeling calculations of the designed lighting. In other words, the UGR score to determine LEED certification must come specifically from software modeling calculations.

The conditions that impact the UGR of a design include fixture selections, room sizes and layouts. A luminaire with higher lumen packages and/or wider distributions may result in higher UGR. Larger rooms may require more fixtures or for fixtures to be spaced farther apart. This can lead to more light sources within the occupant’s field of view and to a potentially higher UGR. Lower ceilings or fixture mounting heights also play a role. The closer the fixture is to the observer’s line of sight, the higher the UGR will be. Understanding how each criteria impacts the UGR before approaching a design and fixture selection facilitates a smoother practice and implementation of this LEED strategy.

It is important to note the exceptions to the glare control path include employing wall wash fixtures, indirect fixtures and specific applications of fixtures. When done correctly, these applications eliminate the possibility of the occupant having a direct line of sight into a light source. This significantly reduces the potential of glare experienced. Therefore, using any of these methods will help achieve either the maximum allowable luminance or UGR.

How are lighting manufacturers helping to meet these credit requirements?

There are a few key changes that manufacturers are providing to aid lighting designers and specifiers when they are attempting to select fixtures that comply with the glare control portion. First, they are making the luminance data and UGR ratings easy to find on all specification sheets. While, this will take some time to be seen across all fixtures and manufacturers, progress is being made.

It is important to understand that the UGRs of an individual fixture do not tell the whole story. They are calculated using a specific set of assumptions — including common room shapes, surface reflectance and observer locations — to provide an average or expected UGR. Therefore, while the numbers provided cannot be simply applied to any design, they can be used to help direct a design’s fixture selection before it’s possible to calculate the overall UGR.

Figure 2: Visual representation of unified glare ratings (UGRs) as experienced in a typical office setting. As the angle increases between the light source and observer’s line of sight, the observer’s visual comfort increases and the UGR decreases. Courtesy: Smith Seckman Reid Inc.

Secondly, many manufacturers are using baffles on fixtures, which improve visual comfort by reducing glare. Baffles are a tool utilized by designers to minimize an observer’s ability to directly see the light source without significantly impacting the light fixtures light output and distribution. A common example often seen are the egg crate baffles on older fluorescent troffers. The baffle options such as a return of the egg crates, that are becoming more widely available will potentially make achieving these credits more feasible without complete changes to designs and fixture types commonly used.

Color rendering

Lighting specifiers will need to remain conscious during their selection process to utilize fixtures with 90 CRI options available. This may seem to be a limiting factor in some cases, but as technology progresses 90 CRI is becoming a standard option on many LED luminaires. In the future, the ANSI/IES TM-30 evaluation may start to replace CRI criteria in fixture selections.

Lighting control

Most designers and specifiers in the commercial design world will be familiar with designing lighting controls systems that meet the intent of this credit, as standard energy codes require this level of control in most occupied spaces. The keywords in this section of the code are “regularly occupied spaces,” where people will be spending their time, working and performing tasks. Owners and occupants often prefer dimming options for the enhanced level of control.

Luckily, designers and specifiers will not have any issues finding fixtures and control packages that have dimming options. Designers and specifiers need to work with the owners and users to determine the best solution for them, if that will be dimming, multiple preset dimming levels or a combination of options.

Surface reflectivity

In general, this strategy will fall into an architect or interior designer’s scope and not have much influence on lighting design and specification. Lighting designers and specifiers should work with the rest of the design team to be aware of the different surface reflectance chosen throughout a space to properly calculate a design’s UGR, if applicable.

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