Warehouses, big box retail and industrial facilities generally utilize high and low bay fixtures for general ambient illumination. The light sources for these fixtures traditionally have been high wattage metal halide and high output linear fluorescent lamps. While these light sources can have a high rated life – up to 40,000 hours, they also require significant energy consumption – 175W to 400W and higher. Because these fixtures generally operate at least 12 hours a day the cost of operation (including utility demand charges) can be high. High efficiency LED fixtures offer the opportunity to reduce these costs.
LED high and low bay fixtures appeared on the scene a few years ago. However, until the last couple of years (2016, 2017), these LED fixtures did not pose a serious challenge to the traditional HID / fluorescent installations primarily because of inadequate lumen output. However, based on recent studies by the United States Department of Energy (USDOE), advances in LED technology and improved manufacturing have allowed LED high and low bay fixtures to close the gap to the point that today they are providing equivalent illumination at lower operating costs than either HID or fluorescent.
The USDOE CALiPER program has been testing LED lamps and fixtures since 2006. The stated objective of the program is to provide “unbiased, trusted product performance information . . . with testing and analysis, conducted by accredited test labs using industry-standard test procedures.” Once evaluation is completed, USDOE publishes a “Snapshot” of their findings as a way to inform the industry and the public on progress (or lack of) for various categories of LED bulbs and fixtures.
The information in this post is based on a 2017 CALiPER study of industrial LED fixtures (including high / low bay).
LED Lumen Output Now Equal to HID and Fluorescent in High / Low Bay Fixtures
Early generation LED high/low bay fixtures failed to produce the lumen output necessary to compete with HID and fluorescent fixtures. Traditional low bay fixtures typically provide between 5,000 and 20,000 lumens while high bay fixtures between 15,000 and 100,000 lumens.
These lumen output levels were not achieved by LED fixtures until 2013. At that time, USDOE listed roughly 150 LED high/low bay fixtures on the market that had lumen output exceeding 15,000 hours. Today, in 2017 USDOE lists over 4000 high bay LED fixtures on the market with tested lumen output exceeding 15,000 lumens. Similar results apply for LED low bay fixtures providing between 5,000 and 15,000 lumens.
LED Fixture Efficacy Surpasses Traditional High / Low Bay Fixtures
As with most categories of LED fixtures, the efficacy (lumens per watt, or lm/W) of LED high/low bay has improved dramatically over the last few years. From levels in the 60 to 80 lm/W for early generation fixtures, today much of the LED high/low bay product on the market tests at levels of between 95 to over 150 lm/W with the mean at 115 lm/W. For reference, metal halide and fluorescent high/low bay fixtures have an efficacy in the range of 70 to 90 lm/W.
To get Design Light Consortium (DLC) qualified product status for the type of fixtures discussed here, the minimum efficacy is 100 lumens per watt. To get DLC Premium status the minimum efficacy is 125 lumens per watt. Many high/low bay LED fixtures are available today that meet one or the other of these DLC standards.
The recent CALiPER report on this fixture type states “A majority of listed industrial fixtures (eg. high/low bay) have comparable lumen output and higher luminous efficacy than their metal halide and fluorescent counterparts.”
LED Color Characteristics Comparable to HID and Fluorescent Fixtures
In addition, other key metrics such as color quality of the illumination from LED arrays in high/low bay fixtures compares favorably with metal halide and fluorescent light sources. The color rendering index (CRI), as tested in the CALiPER program, showed a range of 70 to 80 CRI that closely matches the typical metal halide or fluorescent installation.
The median color temperature of the LED arrays in fixtures trends slightly higher – 5000K – compared to metal halide and fluorescent where 4000K is the norm. That said, many LED industrial fixtures are available with a color temperature around 4000K.
The 2017 CALiPER report concludes that for the key metrics of lumen output, efficacy and the color quality of illumination, industrial LED fixtures match or exceed the values available from metal halide and fluorescent equivalent fixtures.
- Lumen output of LED high / low bay fixtures is equivalent to HID and fluorescent fixtures.
- Efficacy (lm/W) of the LED high / low bay fixtures is significantly higher than HID and fluorescent.
- Color characteristics (CCT and CRI) are similar for LED fixtures and HID / fluorescent fixtures.
Other issues such as rated life, lumen maintenance and cost also must be considered when considering the LED fixture option. In 2015, only 6% of industrial fixture installations were LED. With advances in LED technology and generally declining prices in the last couple of years, the percentage has increased yearly with USDOE projecting that by 2035 over 85% of the industrial fixtures installed in the U.S. will be LED.
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