How to Select the Right LED for High-Bay Lighting

By Gina Roos

Contributed By Hearst Electronic Products


The high-bay lighting market is getting ready for a big shift to LED technology. This is being driven by the falling prices of LED lamps, along with advances in sensors and controls, which are used to help further reduce energy consumption, enabling an acceptable return on investment (ROI). High-bay lighting applications in commercial and industrial environments now are well positioned to take advantage of LEDs in terms of energy savings and minimizing downtime.

Navigant Research (Boulder, CO) forecasts global sales of high-bay luminaires and lamps will increase through 2017, reaching almost $17.0 billion, propelled primarily by the rising adoption rate of more expensive LED luminaires and lamps in new construction and retrofits.

Navigant Research points out that LED technology improvements are also driving the shift, enabling LEDs to meet the tough requirements of illuminating these wide-area spaces "while minimizing contrast, reducing glare, and in many cases meeting strict safety and hazardous environment requirements."

For lighting designers to develop the most cost-effective luminaires that take advantage of LED technology, they need to select the right emitters for the job. These LEDs must be able to meet high-output lumen requirements while simplifying heat management and delivering the right amount of light distribution.

There are many ways to integrate LEDs into high-bay luminaire applications, and there are a number of considerations and/or trade-offs for designers that range from thermal designs (heatsinking) and optical control to driver selection and pricing. Designers of high-bay lighting systems may also want to start looking at incorporating sensors, networking, and other advanced lighting controls to further energy savings and cost reductions, but that is beyond the scope of what we are exploring here. In this article we will take a look at several LED solutions that meet the performance, as well as deliver the cost savings required for high-bay applications, including Cree's XLamp XM-L2 and XLamp XP-E2 and Philips Lumileds' Luxeon R and Luxeon TX.

Cree recommends a six-step framework for designing LED luminaires and lamps (Figure 1). As part of this framework, there are six critical characteristics that designers should evaluate when designing high-bay lighting systems. These include illuminance distribution (footcandles [fc]/lux), electrical power (watts), lifetime (hours), payback (months), luminous flux (lumens), and manufacturability. Other important characteristics include operating temperature, operating humidity (percent RH), correlated color temperature (CCT) (K), color rendering index (CRI), and ease of installation.

Image of Cree’s six-step framework

Figure 1: Cree’s six-step framework for creating LED luminaires and lamps (Courtesy of Cree).

This also means that designers need to keep design goals in mind, which should be centered on several characteristics, including light output (lumens), power, luminaire efficacy, lifetime, CCT, CRI, and power factor, all with minimum and maximum goals.

The Designlights Consortium¹ has put together a list of technical requirements as a guide for high-bay luminaires for commercial and industrial buildings, and high-bay aisle luminaires.

Here are the technical specs for high-bay commercial and industrial buildings:
  • Minimum light output: 10,000 lumens
  • Zonal lumen density: ≥30 percent: 20° to 50°
  • Minimum luminaire efficacy: 80 lm/W
  • Allowable CCTs: ≤5,700K
  • Minimum CRI: 70
  • L70 lumen maintenance: 35,000 hours
  • Warranty: 5 years
Here are the technical requirements for high-bay aisle luminaires:
  • Minimum light output: 10,000 lumens
  • Zonal lumen density: ≥50 percent: 20° to 50°, ≥30 percent: 0° to 20°
  • Minimum luminaire efficacy: 80 lm/W
  • Allowable CCTs: ≤5,700K
  • Minimum CRI: 70
  • L70 lumen maintenance: 35,000 hours
  • Warranty: 5 years
Now let's take a look at some LED examples that meet these requirements starting with two second-generation XLamp platforms: the XM-L2 and XP-E2 LEDs.

Designed for very-high-lumen applications, including indoor, high-bay, and outdoor lighting, the second-generation Cree XLamp XM-L2 single-die LEDs deliver 20 percent more lumens per watt, as well as double the lumens-per-dollar compared to the original XM-L LEDs, which means lighting designers can use fewer LEDs at a lower cost. The LEDs offer up to 186 lumens per watt at 350 mA, at 25°C.

Key features of the XM-L2 include:
  • Available in white, 80-CRI white, 85-CRI white, and 90-CRI white
  • ANSI-compatible chromaticity bins
  • Binned at 85°C
  • Maximum drive current: 3,000 mA
  • Low thermal resistance: 2.5°C/W
  • Wide viewing angle: 125°
  • Unlimited floor life at ≤ 30ºC/85 percent RH
  • Reflow solderable - JEDEC J-STD-020C
  • Electrically neutral thermal path
  • RoHS- and REACH-compliant
  • UL-recognized component (E349212)
Cree also designed the XM-L2 LEDs to be compatible with existing XM-L LED designs, leveraging the 5 x 5 mm XM footprint. “This allows existing customers to easily incorporate the second-generation parts into XM LED designs to shorten the fixture design cycle and improve time-to-market,” said Cree.

Characterized at 85°C, the XM-L2 LED is available in 2,700K to 6,200K color temperatures and offers minimum CRI options of 80, 85, and 90. However, because the XM-L2 LED is a successor product to the XM-L LEDs, the application of Energy Star qualification requires only 3,000 hours of LM-80 data, instead of the normal 6,000 hours, according to Cree.

Another second-generation product suitable for high- and low-bay luminaire applications is the XLamp XP-E2 color and white LEDs that also doubles the lumens-per-dollar and offers up to 20 percent more lumens per watt compared to the original XP-E LED. The XP-E2 LEDs deliver up to 128 lumens per watt at 350 mA, 85°C or 143 lumens per watt at 350 mA, 25°C in cool white (6,000K). They are available in 2,700K to 7,000K color temperatures with minimum CRI options of 70, 80, 85, and 90.

The XLamp XP-E2 color LEDs deliver up to 1,409 mW for royal blue, 109 lumens for blue, 253 lumens for green, 203 lumens for amber, 193 lumens for red-orange and 155 lumens for red, all at maximum drive currents.

Key features of the XP-E2 LEDs include:
  • Available in white, outdoor white, 80-CRI, 85-CRI, 90-CRI
  • White, royal blue, blue, green, amber, red-orange, and red
  • ANSI-compatible chromaticity bins
  • White binned at 85°C
  • Maximum drive current: 1 A
  • Low thermal resistance: as low as 5°C/W
  • Wide viewing angle: 110°-135°
  • Unlimited floor life at ≤ 30°C/85 percent RH
  • Reflow solderable - JEDEC J-STD-020C compatible
  • Electrically neutral thermal path
  • RoHS-compliant
  • UL-recognized component (E349212)
As with the XM-L2 platform, the XP-E2 can increase the lumen output of the original XP-E designs at the same cost and power or lower the system cost by using fewer LEDs. This also speeds up time to market thanks to a minimal redesign required to upgrade performance. The XP-E2 LEDs also use the same XP footprint (3.45 x 3.45 mm) and are optically compatible with all XP LED designs.

Like the XP-L2, the XP-E2 LEDs, as a “successor” product to the original XP-E LED, only requires 3,000 hours of LM-80 data instead of the normal 6,000 hours, which speeds up the qualification of the luminaires.

Philips Lumileds also offers several LED products that can be used in high-bay and low-bay luminaire designs. Application requirements include increased optical control to optimize luminaire spacing, uniform lighting, accurate color rendering for readability and safety, instant-on without a loss of reliability, and dimming and occupancy-based control features, according to Philips.

One good example that meets these requirements for high-bay luminaires, as well as a variety of other applications, is the LUXEON R LED family from Philips Lumileds. All LUXEON R LEDs are hot tested (Figure 2) and specified at real-world operating conditions of 700 mA, TJ = 85°C, and feature "Freedom from Binning," which means that every LUXEON R LED falls within a single five-step MacAdam ellipse (color space centered on the ANSI CCT color bins). This ensures that lighting manufacturers will get color consistency from LED to LED.

Image of Philips Lumileds LUXEON R emitters

Figure 2: All LUXEON R emitters at test current: relative light output versus junction temperature (Courtesy of Philips Lumileds).

The LUXEON R also is footprint compatible with LUXEON Rebel and LUXEON Rebel ES, while delivering more light output, higher efficacy and better quality of light. These LEDs offer a minimum CRI of 70.

Key specifications of the LUXEON R include:
  • Hot tested and specified at TJ=85°C
  • Freedom from binning: < 5SDCM
  • CCT: 3,000K, 4,000K, 5,000K, 5,700K, 6,500K
  • CRI minimum: 70
  • Minimum flux: 160 to 200 lumens
Another Philips platform family that can meet high- and low-bay lighting, as well as a variety of other applications is the LUXEON TX platform, which is available in a range of CCTs and CRIs. With this line, Philips added a minimum 85 CRI option for greater design flexibility and product differentiation.

Previously, Philips said designers had to select either lower efficacy associated with a 90 CRI LED or poorer color rendering associated with an 80 CRI LED. The LUXEON TX is said to bridge the gap between the two by delivering high CRI with increased efficacy in a CCT range from 2,700K to 5,000K.

Here are some of the key features of the LUXEON TX:
  • Compact 3737 package
  • Typical VF of 2.8 V and thermal resistance of 3K/W
  • Hot tested at TJ = 85°C
  • Freedom from binning: – 3 and 5 SDCM
  • Exceeds Energy Star lumen maintenance requirements
  • UL-recognized component [E352519] with level 4 enclosure consideration
In summary, engineers need to take a number of factors into consideration when designing their high-bay luminaires, including thermal management issues, such as proper heatsinking, selecting the right driver among the multiple driver options available, and choosing the right LED that meets the necessary technical specifications, encompassing power, lifetime, light output (lumens), CCTs, and CRI. Cost requirements of the design must also be seen as a factor. Designers that take these characteristics into account early in the design will develop highly-efficient lighting systems at the right price point.

For more information about the parts discussed in this article, use the links provided to access product pages on the Digi-Key website.

References:
  1. The Designlights Consortium
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