Troffer Evolution

The new generation of premium troffers offers higher fixture efficiencies - around 90 percent, compared to as low as 65 percent for many conventional parabolic troffers. LITHONIA

The problem with parabolic fixtures is that, while they reduce glare on computer screens, they are often said to create harsh shadows and a dim atmosphere. In particular, this type of fixture tends to produce strong scalloping on nearby walls, resulting in an atmosphere commonly called the "cave effect."

"Parabolics create shielding at high angles to reduce glare," says Grant Hukle, senior product manager, fluorescent lighting at Day-Brite Lighting, Tupelo, MS. "The drawback to this approach is that the upper spaces of the room are then dark, which makes the room feel darker and smaller than it actually is, as well as creating significant contrast on the walls."

The question is not whether parabolics are effective; it's whether they are even needed anymore. Computers have changed over the years. Today's screens have less curvature, as well as improved screen brightness and anti-reflectance technologies. Flat LCD screens are becoming increasingly popular, and software developers typically rely on positive contrast (dark characters against light backgrounds) to present information. Such advances have virtually eliminated the sensitivity of computer screens to high-angle brightness.

As a result, a new type of fluorescent troffer has been introduced in the past few years and is gaining in popularity, both for its energy story and its potential impact on visual comfort and lighting quality. Possibly better known as "volumetric lighting," a term popularized by Lithonia Lighting after it introduced RT5 in 2004, this fixture type is also known by other terms such as "diffuse lighting" or "full distribution lighting." For purposes here, "premium troffer" will be used as a generic descriptor.

A premium troffer is a fluorescent troffer with a photometric distribution that includes a small amount of light in the 60- to 90-degree zone, tapering off as the angle gets closer to 90 degrees. "With a better balance of luminance throughout the visual field, the space feels brighter, larger, more open, more relaxing," says Steve Lydecker, vice president commercial fluorescent for Lithonia Lighting, Conyers, GA. "Facial rendering is more natural, consistent, and complimentary. Shadows tend to be softer and less pronounced. The appearance of the space is less defined by sharp, arbitrary transitions in surface brightness. This type of lighting does a better job of rendering architecture, its contents, and its occupants true to form."

Premium troffers compete against older-design parabolic and conventional troffers at the low end, updated parabolics and "basket" recessed fixtures introduced in the 1990s in the middle, and direct/indirect fixtures at the high end. Updated parabolics and basket fixtures provide some of the same benefits as premium troffers, but fall short in the high-angle light control (basket fixtures) and fixture efficiency (baskets and parabolics). Premium troffers are specified in offices, schools, healthcare facilities, retail spaces, such specialized public spaces as airports, and other environments where general ambient fluorescent lighting is used. The architectural aesthetic of these fixtures is well suited to upscale offices and similar commercial applications. While not common in retail environments, the higher vertical uniformity is well suited to applications with racks or shelves.

"These could be new architectural-style products or updated parabolic fixtures that have been designed to boost efficiency and offer a higher portion of vertical light," says Keith Hall, director of marketing and product development for Metalux at Peachtree, GA-based Cooper Lighting. "These units tend to be designed with higher efficiencies and use new lamp/ballast technology. Higher vertical light levels add to a perception of more light in the space, allowing energy to be reduced while still meeting the end-user's needs. The benefit is more light for less energy."

Premium troffers direct a carefully controlled amount of light into the upper spaces of the room - more than a parabolic, but less than a conventional troffer. Their photometric distributions have the highest candlepower directly below the fixture, tapering off smoothly as the angles get closer to 90 degrees. LITHONIA

Premium troffers may feature (concealed) T5, T5HO, T8, or compact fluorescent lamping and are available in different sizes - and, in some cases, depths to accommodate various lighting needs and ceiling types. The latest trend in premium troffer design is a fixed lamp cross-section. In other words, the fixture can be specified only with a specific number and type of lamp offered by the manufacturer. For example, a two-lamp T8 fixture cannot be specified as a three-lamp T8 fixture, and so on; instead, the fixture optics are optimized for a specific number of lamps. The benefit of this is higher fixture efficiencies - around 90 percent, compared to as low as 65 percent for many conventional parabolic troffers - with two-lamp units producing comparable light output as conventional three- or four-lamp troffers. This higher efficiency means a significant percentage of lamps can be eliminated from the design, which means, of course, higher energy savings by leveraging fixture efficiency in addition to lamp and ballast efficiency. If more or less light output is needed, different lamp/ballast combinations can be specified to tune output to the application need.

"Another consideration is that premium troffers generate smooth lighting throughout the space rather than only in selected areas below the fixtures, which makes the lighting system much more adaptable to any changes in the configuration of the space," says Hukle. In some office lighting designs, workstations become focal points in the illumination design, with light concentrated on the desktop and tapering off between workstations. Workstations, however, may have to be moved. "Uniformity is important considering how much portability today's equipment has - things like partitions that move and laptops that are used in many locations, rather than fixed computers on desks."

While still a small part of what is largely a highly commoditized lighting category, Lydecker says premium troffers are the fastest-growing segment of the North American lighting market. As energy codes continue to become more stringent and sustainability continues to grow in popularity in construction, look for premium troffers to proliferate in high-end office, school, and other commercial projects.

Craig DiLouie ([email protected]), a lighting industry journalist, analyst, and marketing consultant, is principal of ZING Communications.