LED Fixture Efficacy vs Quality of Light: Recent Study Provides Insights

For several years, the mantra around LED lighting has been the significant rated life and efficacy (lumens/watt) advantage it has over most other light sources.

  • Longer life means fewer bulb changes which translates into reduced maintenance costs for facilities.
  • Better efficacy means lower energy costs.

Both of these advantages are quantifiable and allow a straightforward return on investment analysis.

Today, there is no question that LED lighting can provide cost effective solutions for many commercial and industrial applications.

Recently, however, there has been concern around a manufacturer push to ever higher levels of efficacy. Partly caused by the higher efficacy requirements to qualify for Design Light Consortium (DLC) Premium status, manufacturers are also driven by the perception that LED purchase decisions are being made with a focus on energy efficiency. The higher the efficacy the better chance they have to get their products specified and purchased.

The question some in the industry are asking: Are quality of light compromises being made to achieve efficacies that have reach has high as 200 lumens/watt?

This issue warrants a closer look.

2018 DOE Study Evaluates High Efficacy LED Fixtures

Recently the U.S. Department of Energy (DOE) tested a batch of commercially available, high efficacy LED fixtures designed for low and high bay applications. In addition to evaluating and comparing the manufacturer photometric claims, the study also conducted subjective evaluations of the lighting that was installed to simulate low bay applications. These subjective evaluations directly address the issue of efficacy vs. light quality.

Characteristics of the LED Fixtures In The Study

  • All fixtures in the study were rated at 5000K, the normal color temperature for low and high bay applications.
  • The DOE tested lumen output for the fixtures ranged from 16,000 to nearly 22,000 lumens
  • The DOE tested efficacy ranged from a low of 136 lm/W to 200 lm/W.
  • Additionally, most of the fixtures did not have diffusers covering the visible LED arrays. The fixtures that did have a diffuse cover were also the ones that measured lowest in light output.

Visual Evaluation Process and Results

A group of over 20 evaluators – lighting specifiers, energy efficiency specialists, facility managers – observed mockups of fixture pairs. These observations took place over several days with the observers viewing the fixture pairs in randomized order. No brand or model identification of the fixtures was visible. The observers were not told about the focus of the study. They simply were asked to take notes about their perception of the lighting.

The responses pivoted around the viewers perception of glare and lighting uniformity. For the lighting the evaluators found most appealing, they used terms such as “soft shadows”, “good glare control”, “nice appearance” and “excellent visual comfort”. The least appealing light illicited comments such as “high glare”, “sharp shadows”, “no good viewing angle” and “luminance [brightness] way too high”.

The group of fixtures with the lowest perception of visual comfort generally featured open strips of LEDs without glare control such as diffusers. These were also the fixtures with the highest efficacy – up to 200 lm/W.

The most positive comments about the illuminated space singled out fixtures that provided the most light distribution and glare control. These were also the fixtures with the lowest efficacy (still over 130 lm/W). The lighting was described as more uniform, fewer shadows on the work surface and significantly less direct glare. The DOE study states that diffuser covers on fixtures lower efficacy up to 16% but produce more uniform, low glare lighting environments.

The DOE researchers noted that as the mounting height increases from low bay to high bay, for example large warehouse installations, the direct glare problem may not be as significant. In addition, choosing a 4000K rather than 5000K fixture may lower the perception of glare. Higher color temperatures (more blue spectrum light) generally produce more lumens which boosts these fixtures into the highest efficacy range. According to the DOE, changing from 5000K to 4000K will result in up to a 13% drop in efficacy.

DOE Conclusion

The main conclusion in the DOE test report is that efficacy should be only one of many attributes to consider when selecting LED fixtures.

Light distribution and glare are two very important attributes that seemed to be sacrificed by manufacturers looking to push the efficacy has high as possible.

Uniform lighting on the work surface, with minimum shadows, and no direct or reflected glare improves occupant comfort, productivity and, in industrial spaces, minimizes accidents caused by the lighting.

While the DOE study focused on linear low and high bay LED fixtures, these observations apply generally to LED lighting – both indoor and outdoor commercial / industrial applications.

Other Commentators Offer Opinions On This issue

John Burns of Global Tech LED, in a 2016 LEDs magazine article, talked about how the focus on efficacy in LED products was potentially harming the lighting industry. He singled out the DLC Qualified Products List for encouraging manufacturers to focus on efficacy by frequently raising the efficacy standards. The DLC’s newer classification of “Premium” products has set the efficacy bar even higher. The requirement for Premium status varies by application, but generally it must meet or exceed 120 lm/w.

According to Burns, The problem is that most premium-efficacy LED products must use many more LEDs on their circuit board and thus lose the ability to apply lensing to control the light distribution. This results in terrible implications in the quality of light delivered by these products.”

In other words, non-uniformity of light distribution and glare may be the trade-offs that come with the highest efficiency LED fixtures.

However, the DOE study also showed that when manufacturers of very efficient LED fixtures include diffusers or baffle light control, the efficacy may be 15% or so lower than without light control, but the quality of illumination will be significantly better than competing products with higher efficacy.

Furthermore, the fixtures with built-in light control still had efficacies up to 130 lm/W proving that both high efficiency and quality light can be achieved in an LED fixture.

Guidance for Specifiers and Buyers

Specifiers, building owners and facility managers should use the DLC efficacy metric as a starting point when considering fixture options, but additional information from the manufacturer may be necessary to learn what features are built-in to the fixture to help ensure a level of lighting quality that will produce a productive and comfortable work environment.

The DOE report conclusions went further, encouraging specifiers and buyers to see the products, with all the attributes they want, in an installation similar to their application before specifying or making a purchase. Alternately, they should purchase a couple of fixtures initially and install them to make sure the lighting meets their expectations.

Download the full DOE report.

Shop High Efficacy LED Fixtures With Built-in Light Control

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Dave Burtner

Dave has been active in the lighting industry since 1994. Formerly a member of the Illuminating Engineering Society of North America and certified by the National Council On Qualifications for Lighting Professionals, Dave now writes blog posts, lighting tips and provides lighting product assistance for the Topbulb website.

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