Essentials of designing with LED

LED lighting design has many advantages over previous lighting sources, enabling designers to deliver more to their clients.
By Sara Schonour, LC; Barrett Newell; and Victoria Riedinger; CannonDesign, Boston August 21, 2018

Learning Objectives

  • Identify key characteristics and functional lighting advantages of LED technology.
  • Understand how to apply LEDs to support project-specific lighting goals and criteria.
  • Understand considerations and coordination items required to design a project using LED systems.

LED technology offers several key advantages over legacy lighting sources, enabling lighting designers to deliver more to their clients. With proper identification of LED opportunities at the onset of a project and thoughtful coordination of the systems and equipment needed to achieve the team’s design goals, these advantages are leveraged to create lighting solutions that are more sustainable, flexible, and maintainable than before.

Before diving into product selection and lighting layouts, designers should always begin by assessing the needs of their clients. Each project is unique in size, shape, and geographical location, let alone programmatic and stylistic requirements, which call for a fresh set of lighting solutions at the onset of each endeavor. A client’s opinions on the way they’d like their spaces to look, feel, and function and their energy efficiency goals will have a direct effect on the designer’s approach in establishing the project’s sustainability guidelines, as well as determining color temperature, color-rendering requirements, and other design criteria.

One of the biggest advantages of LED technology is the ability to save energy. LED technology is continuously advancing, and with that comes improved energy efficiency. Today’s LED boards and drivers are able to produce more light at lower wattages than the majority of older lighting technology-many manufacturers now have the ability to provide products with 100+ lumens/W. As lighting-power density (LPD) requirements for building codes become more stringent and sustainability certifications become more prevalent, the efficacious lumens per watt provided by LEDs become necessary elements to include in the design of energy-efficient lighting systems.

Figure 1: This cafeteria uses linear lensed LED slots, curving LED tapelight, backlit stretched ceiling with LED arrays, recessed LED downlights, and suspended LED cylinders. All graphics courtesy: Cannon Daylight harvesting

Access to daylight can contribute significant energy savings within a building. Whether required by code or installed for best practice, photosensors monitor light levels in a space and adjust fixture outputs to maintain a footcandle level acceptable to the space. As the LEDs are dimmed, the current supplied to the fixtures decreases, lowering the wattage required to power the fixture.

The energy usage is fairly linear when dimming LEDs, meaning when reduced to 50% they are using roughly 50% of their full energy consumption, depending on the quality of the driver. Along with the energy savings, daylight controls also provide the benefit of longer fixture life. As LEDs dim in response to higher daylight levels, the lower drive current to the LED boards produces less heat, which prolongs life. The more daylight dimming control in a building, the longer the fixtures will last.

The low power consumption of LEDs enables greater efficacies, and their ability to be easily controlled allows them to be leveraged for daylight harvesting and other energy-saving control strategies. The resulting energy savings can be significant-often upward of 35% to 40% when compared with legacy systems like fluorescent, incandescent, and high-intensity discharge (HID)-making lighting a major contributor to project sustainability.

Sustainability requirements are determined by a number of factors, but the most basic design drivers are the codes and standards established by local governing bodies. The assigned code can greatly affect the lighting design and fixture criteria, making early consideration critical. These standards must be met in order to obtain approval to construct.

Codes, standards, and guidelines

Relevant codes for lighting design include but are not limited to the International Building Code (IBC), International Energy Conservation Code (IECC), and ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings. While there are variations within each code, these codes establish LPD metrics, emergency and egress light levels, and minimum lighting control strategies as the major requirements. Each code has multiple editions and is updated regularly (typically a 3-year cycle), as technology changes drive improved efficiency and safety requirements.

The version of code is assigned to a project based on the start year and the building standards that the local governing body follows. Some areas of the country follow stricter codes-such as California’s Title 24-making it important to stay up to date with lighting requirements in various regions.

Another strategy for addressing sustainability is choosing to design to the U.S. Green Building Council’s LEED guidelines. The LEED system establishes a checklist of design guidelines to follow, but unlike building codes, designers don’t have to satisfy all items. The more sustainable strategies incorporated into the building design, the more points earned, and the higher the level of certification received: LEED Platinum, Gold, Silver, or Certified can be achieved through sustainably focused design.

There are slightly different checklists for different project typologies, but each contains several credits related to lighting, which include control strategies, building LPD, lighting-fixture quality, daylighting, and other best practices. These credits are significantly more achievable with LED technology. Like codes, LEED is updated as technology improves, and the current version is LEED v4. Other certification programs, like the WELL Building Standard, are emerging with a slightly broader range in addition to a focus on energy efficiency and the role lighting can play.

Flexibility in design

In addition to energy efficiency, LEDs offer flexibility in design options, such as correlated color temperature (CCT), which is the color of light being emitted from a fixture. LED technology is available in an array of CCTs that can be implemented into a project, allowing the program itself to drive the decision.

Typically, hospitality projects tend to favor a warmer CCT, ranging from 1800 to 2700 K. Residential applications typically use 2700 or 3000 K, mimicking the color of the incandescent and halogen lighting usually found installed in homes, while corporate commercial spaces use 3000 to 4000 K, similar to the fluorescent range we have become accustomed to. Hospitals, labs, and other environments where a fresh, clean, "sterile" appearance is desired tend to use a cooler 3500 to 4000 K CCT. Educational projects can differ in CCTs, from 3000 to 5000 K, depending on the age of the students, the subject being taught, and the mood the teacher is looking to create.

The ability to vary CCT is an emerging technology that many LED manufacturers are now able to offer to allow for these types of desired flexibility. Unlike older technologies, (static white) LEDs retain their color temperature regardless of their dimmed level. As we know from living with traditional incandescent sources, their light becomes warmer as they dim, which is an expected and desired effect in many residential applications.

With the flexibility of LEDs, "tunable white" and "warm dim" technology, now available from many LED manufacturers, allow a single fixture to provide an adjustable range of color temperatures. Populating boards with a variety of colored LED chips enables multiple CCTs to be emitted from one fixture, allowing clients a full range of color at full output as well as an incandescent-like dimming performance. Many types of LED fixtures are also available in full color-changing varieties, enabling a near-limitless palate of design options.

Figure 2: Daylight penetration was studied at the Vermont Agriculture & Environmental Laboratory in Randolph Center, Vt., to understand the available energy savings that could be captured by dimming electric lighting when ample daylight is present. Design Color rendition can also play a critical role in the selection of a lighting product, and LEDs offer improvements in color rendering over legacy technologies like fluorescent and many HID sources. Traditionally, the metric used to evaluate color rendition has been the color-rendering index (CRI), and along with CCT, CRI can greatly affect the appearance and perceived color of materials in a space.

A higher CRI will present colors that more closely match colors lit with natural light, while a lower CRI will distort and diminish color vibrancy. Today’s LED sources typically deliver 80+ CRI, with options for 90 CRI or more, and some sources reach as high as 97 CRI.

Special consideration of CRI is necessary for applications that have a particular emphasis on visual appeal, such as museum projects that require lighting to highlight artwork or retail installations where color is especially important.

Color rendering

The original metrics used to determine good color rendering-the incandescent lamp and the 14 pastel reference colors-are being challenged by other ways of assessing color preference as a result of the way LEDs create light. The chemical mix that creates the "white" light of a particular CCT can be adjusted to provide more intense saturation of hues, creating a more vibrant color rendition. Technical Memorandum 30-15: IES Method for Evaluating Light Source Color Rendition was recently introduced by the Illuminating Engineering Society to offer a more comprehensive approach to color rendition.

Unlike traditional lighting sources, LEDs have the ability to provide colored light along with a wide range of white light, although LEDs themselves are not inherently white. Based on the manufacturing approach, they can be various saturated hues of red, green, blue, yellow, and others that are either mixed or coated with a phosphor to produce a light that the human eye perceives as white.

RGB (red-green-blue) and RGBW (red-green-blue-white) technologies mix the color from the various chips to create the majority of visually perceivable colors, and RGBWA (+ amber) and RGBWM (+ mint green) are new mixes that introduce even more options by filling gaps in the color spectrum previously missed. Paired with ever-simplifying control technology, like touch screens and cloud-based apps, clients can take advantage of hundreds of options at the push of a button.

LED sizing

The small size of the LED package is another benefit of LED technology. Traditional sources like linear fluorescent, incandescent, and HID can be limiting due to their larger housing sizes and heat-dissipation requirements. With LED’s reduced size, low heat emission, and different requirements for heat management, this source can be placed in smaller housings and extrusions and still produce similar lumen output.

LEDs are getting tiny in comparison to traditional sources, often measuring only a few millimeters in depth and width, making them ideal for small form factors. LED tape light, a common lighting tool, is widely used in linear applications requiring moderate output, such as step lights or under-cabinet lights. What used to require a space the width of a fluorescent or compact fluorescent tube can now be achieved in an extrusion as small as 0.5×0.5 in.

As a point source, LEDs are inherently directional, making them very efficient sources for many traditional lighting applications that require directed light. A raw LED sits on a circuit board and generally gives off a 120-deg beam in all directions, so optics are required to mold the shape of the light. Lenses, reflectors, total internal reflection (TIR) optics, and other optical technology can be employed to shape the beams of light to fit the application, and many manufacturers offer field-adjustable optical kits to enable flexibility and future-proofing.

Along with single-chip sources and flexible tape light, LED modules have come to replace linear fluorescent lamps in many applications. These modules can vary in length and shape, giving "to the inch" design precision. This modularity has allowed for customizable lengths and configurations, giving designers far more freedom to be creative in integrating lines and planes of light into their designs while capitalizing on the benefits of energy efficiency and minimized product footprint.

Unlike traditional sources, when LEDs fail, they will typical fail immediately upon start-up. Otherwise, their brightness diminishes over time, losing light output slowly. An LED product’s useful life is expressed as its L70 value, which indicates when it only has 70% of its original lumen output. 50,000 to 100,000 hours are a common range for L70 values, with some LEDs testing higher and retrofit LED lamps typically testing at 15,000 to 25,000 hours. While the long life of LEDs is a key ease-of-maintenance benefit, it’s important to remember that the driver is typically the first component of an LED product to fail. Driver maintenance can extend the overall life of fixtures, saving money for clients over time, and attic stock for common driver types is recommended.

Figure 3: “Cooler” color temperatures to the left, appearing more blueish in tone, are represented as higher Kelvin values. Lower values appear “warmer” and yellowish in tone, mimicking traditional incandescent sources.  Coordination and integration

In addition to having to bear in mind all of these considerations, every project has another thing in common: the need for coordination. Each moving part of a project-whether that be architecture, mechanical, electrical, plumbing, structural systems, lighting, or site-and each discipline has an effect on the other. Ensuring that the balance of proper coordination between each is maintained is key to any project’s success.

With the advancement and prevalence of LEDs, creative options have grown exponentially, and flexibility is at an all-time high. With this shift, a new set of coordination needs has developed. Lighting integration and details that were never possible with antiquated sources due to their size and ability to deal with heat can now be a reality, with endless options of fixture and component combinations, configurations, and sizes. Close collaboration between the design team, often across trades, is required to develop the specific details sized to accommodate whatever form factor the fixture selected for the job requires. Similarly, with the advancement of optical technology, the engineered designs often require specific setbacks from walls and precise spacing criteria, requiring increased coordination with ceiling-grid locations and details.

Another crucial coordination item is dimming control. While many LEDs can inherently dim with readily available dimmers, the driver and the control device need to be carefully coordinated to ensure a fully functioning dimming LED system. Improperly coordinated dimming control can lead to a host of issues including reduced dimming range, flickering, buzzing, dead travel, pop-on, drop-out, staggered dimming, strobing, or flashing.

When specifying a dimmer for an LED, verify that the LED has a dimmable driver. Assure the dimming range of the driver meets the specific application-different drivers have different dimming ranges, with "dim to 10%" being common but lower levels and "fade-to-black" options also available. The driver’s dimming protocol and the controller’s dimming protocol must match-dimmers need to "speak" the same language (protocol) as the driver. Common protocols are 0 to 10 V, digital multiplex (DMX512), digital addressable lighting interface (DALI), TRIAC, and electronic low voltage. Most are readily available components of typical lighting control systems.

Lastly, understand any wiring requirements, maximum load limits, minimum load requirements, and limitations of distance or voltage drop for the dimming system. Each dimming protocol is slightly different in its configuration.

While controls are becoming more complex, the sophistication of the systems has opened the door to interconnected systems, which promise to ultimately simplify our relationship to buildings and the control of their systems. From digitally addressable lighting control solutions scalable to the individual fixture to wireless control systems to kinetic switches requiring no electricity at all, we already are able to specify advanced systems that can save energy and give owners practically unlimited control. The internet of things revolution, Power over Ethernet and 24/48 V-distribution exploration, solar direct to grid, and other smart technologies further leverage the inherent capabilities of the microprocessor-based LED system. As these technologies develop, we expect their integration into lighting products to continue to push the boundaries of systems control.

The advancement of LEDs has revolutionized the lighting industry, opening doors for unique and adaptable lighting design solutions. Today’s varied options for color temperature, color rendering, form factor, and controllability make LEDs a powerful design tool that allows lighting designers to meet the specific needs of their client while delivering more energy-efficient solutions than ever before. Continued advancement will only further that trend before the next technology breakthrough enters the market.

Sara Schonour is an Associate IALD and leads the CannonDesign lighting studio and couples her extensive lighting design experience with a deep understanding of architectural design and building systems to bring seamlessly integrated solutions to clients. She is a 2017 40 Under 40 award winner. 

Barrett Newell is a Junior Associate IALD and brings an understanding of the built environment and an appreciation for the importance of integration between design disciplines to each CannonDesign project team she engages, understanding how to use light as a medium to orchestrate unique experiences through carefully executed lighting solutions. 

Victoria Riedinger is a Junior Associate IALD and Intern LC and strives to produce a beautiful and sustainable lighting strategy, recognizing the importance of collaborative design and fulfilling the CannonDesign client’s needs.

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