Acceptable Operating Conditions
Lighting class LEDs offer advantages in cold weather starting and low temperature applications where fluorescent/high-intensity discharge (HID) sources have typically struggled. A T5 fluorescent lamp produces a maximum efficiency of around 35°C and a T8 of around 25°C. LED luminaire acceptable operating temperatures range from product to product but are available with maximum ratings of 35°C or better but require some de-rating to light output above 25°C. Design professionals should contact the manufacturer for a lumen depreciation curve of the product as it is not always published.

Flexibility

A narrow aperture, continuous-run luminaire made up of overlapping 3-foot and 4-foot fluorescent lamps creates some limitations when specifying custom lengths. Similar LED luminaires have the ability to be specified within a ¼ inch for custom lengths. This is a major freedom for the design professional wanting to have light from wall to wall.

Reflective materials used on inside of luminaire maximize efficiency. Photo by Hyexposure Photography

 

Appearance

Appearance of the lens is one of the most obvious elements to be criticized because it is the first thing to be seen. Continuous run luminaires using fluorescent lamps typically overlap tubes for unbroken lines of light. Due to the physical character of a fluorescent lamp, bases/sockets and imperfect reflectors create socket shadows and other visually degrading elements tolerated for many years because the fluorescent lamp was the best thing out there. The lens luminance (brightness of the lens) for a linear LED luminaire can be nearly flawless from edge to edge—a welcomed advantage for high-end architectural applications.

Linear fluorescent is often used in a continuous run. Photo courtesy of Selux

 

Specifying Linear LED Luminaires

Challenges persist as LED technology develops, which acknowledges the unique properties of each product. This, in turn, requires informed specification on the part of design professionals.

Binning

One challenge for the luminaire manufacturer—and the end user—is binning, where LED producers separate their production into lumen, color and sometimes voltage bins. By ordering a wide range of binned LEDs, a luminaire manufacturer receives a better price and improved lead time. On the downside, the variability of luminaire performance is substantially increased, creating high probability for negative impact to end-use customers.

For ENERGY STAR certification, luminaires are required to meet the ANSI C78 377A bin standard (seven-step bin). Even so, luminaires may still have some degree of perceivable color variation. This is acceptable for most commercial lighting applications. But for museum or retail lighting, say, specifiers need to ensure that luminaires meet rigorous color requirements.

Top luminaire manufacturers likely use LEDs from a two-step or four-step bin to maintain color uniformity throughout a product. It may be easier for the end user to understand what they are getting if expressed as a CCT tolerance (e.g., 3,000K LEDs from a two-step bin may be +/-125K from specified CCT meaning LED CCT range could be 2875K - 3125K).

Some luminaire manufacturers may record LED bin information for every job sold to allow future orders to match when installed. It may be necessary for future additions/project add-ons to have new generation LED luminaires preset at the factory to a dimmed level for matching the light output of an older generation installation.

Determining End of Useful Life

A challenge not yet addressed wholly by the industry is determining an LED luminaire's end of useful life. Certain applications may be more sensitive to this than others (e.g., a custodian closet versus a higher security high traffic area of a building). End-of-life indicators in the form of a visual signal are in the works; some examples may be a red indicator light or a luminaire blinking periodically to indicate 70 percent lumen output.

Ambient/Environmental Conditions

When considering applications requiring certain listings design professionals should be sure to verify that the product is adequately listed. This is quite important for LED luminaires when it comes situations like dry-damp or wet locations. IC rated means a luminaire can be installed in direct contact with insulation. Without an IC rating, a 3-inch space must be maintained around the luminaire when installed. The ambient temperature of on installation should be coordinated with the published maximum operating temperature for the LED luminaire selected. Wall mounted luminaires less than 80 inches from the finished floor require ADA compliance. An ADA-compliant luminaire will not protrude more than 4 inches from the wall.

Judging Light Output

An experienced design professional could predict approximately how much light output to expect if he or she knew quantity and type of lamps used. With LED luminaires it is necessary to take a deeper look into the product data sheet/photometry files to determine light output. Simply going by wattage could produce a result that is far different from that expected from a particular product. Similar linear LED luminaire products can actually vary greatly when it comes to light output.

Conclusion

Multiple commercial and governmental forces are driving the development of LED technology which is expected to represent 36 percent of luminaire sales for the general illumination market by 2020 which translates into energy savings of 19 percent. New LED components, materials, and design updates are delivering energy efficacy performance levels unseen until recently. Already, linear LED luminaires are providing a viable alternative to the traditional fluorescent tube with such features as increased length of life, efficacy, energy efficiency, and design flexibility and appearance. But the quality and performance of LED products varies among manufacturers. Design professionals are therefore urged to become familiar with the organizations supporting LED technology and discuss particular specification questions with manufacturers.

ENDNOTES
1	Life-Cycle Assessment of Energy and Environmental Impacts of LED Lighting Products
	Part 1: Review of the Life-Cycle Energy Consumption of Incandescent, Compact Fluorescent, and LED Lamps Part 2: LED Manufacturing and Performance
	February 2012 Updated August 2012, Prepared for: Solid-State Lighting Program, Building Technologies Program, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy Part 1 prepared by Navigant Consulting, Inc. Part 2 prepared by Pacific Northwest National Laboratory N14 Energy Limited

 

Selux offers a comprehensive range of high-quality interior and exterior architectural luminaires with advanced LED and optical design. Selux innovative luminaires are designed to help lighting professionals and architects create exceptional interior and exterior spaces in which to live and work. www.selux.us