Available lighting design software tools support architects, engineers, and designers with the calculation and simulation of luminance levels and even correlated color temperature (CCT), but little is available for on-site verification tools. Nevertheless, verification can insure conformance for specific application requirements such as detailed task-work, food inspection, color critical viewing, warehouse isles, safety exit signs, roadway lighting, etc.
This paper describes a novel solution combining existing CAD lighting design software, on-site measurements using spectroradiometers and imaging illuminance meters, and new lighting auditing software to report and verify detailed performance metrics of the actual end-use environment. This is particularly useful for assessing the unique spectral and light quality characteristics of LED-based lighting.
Published by Miko Przybyla and James S. Summers at 2018 IES Annual Conference Paper Session, Boston
I. MOTIVATION
Citius, Altius, Fortius, is Latin for ”Faster, Higher, Stronger”. This Olympic slogan could easily be adopted to the entire modern LED lighting industry, which is evolving rapidly indeed. Almost every member of the industry is striving to deliver faster, better and more reliable products. At the same time, with the increasing number of technical possibilities and expanding knowledge about the influence of light on people, customers often struggle to differentiate the good from bad and make informed selections of components and products.
Fortunately, the field of LED product quality assurance has been quite active as well. Many standards and system solutions have been developed and the industry is readily adopting them in R&D and manufacturing environments. Today, much of this work is focused on improving product performance, efficacy and compliance. This demonstrates great progress on the design and manufacturing side, but a large gap still exists between that side and the actual final conditions in the end-use environment.
Fig. 1 An award winning Modern Lighting Audit Concept
This gap is further widened by newer requirements such as the WELL Building Standard or the California Title 24 building code are incorporated. Couple that with the differences between theoretical calculations and modeling performed in CAD lighting software, vs. the real-life installed result, and it becomes apparent that on-site verification is prudent. A closed-loop approach, where compliance between the original design/specification and the final result is achieved would be optimum. It should also be simple to use in the field.
II. OLD STANDARDS, NEW METRICS
Traditional approaches to on-site lighting audits typically focus on two most important photometric quantities of illuminance or luminance, included in the majority of lighting standards. Generally available CAD-based lighting design software also employs these qualities, and possibly generalized CCT data. Lighting designers and lighting engineers thereby employ these characteristics during both design stages and, hopefully, as verification for delivered solutions.
Note the above-mentioned process is based on photometric data only, providing quantitative information about the amount of light and possibly CCT. Meanwhile, our knowledge of how light impacts the human body and our performance has dramatically improved and lighting technologies have evolved to improve our well-being. Lighting manufacturers, designers and engineers from many fields are ready to embrace new methods that help illustrate their value-add proposition for superior products, systems, and delivered results. Consequently, there is a need for expanded metrics and measurement systems to support verifications. Fortuitously, existing measuring metrics more commonly used by luminaire manufacturers, as well as new photobiological metrics, can be adopted for lighting audit processes
Today, most of these metrics are not yet incorporated into lighting audit requirements by international standards organizations, but things are clearly moving in that direction. For example, the measurement of spectral power distribution (SPD) allows calculation of the newly approved color rendering indices according to IES TM-30, providing a much more accurate predication of color appearance vs. a simple CCT metric. Equivalent Melanopic Lux (EML) an important metric related to human sleep suggested by the Lighting Research Centre (LRC) and used by the WELL Building Standard to verify circadian lighting influences, also requires SPD information. PPFD, important to plant biology, uses spectral data as well. Similarly, advanced instrumentation allows measurement of flicker parameters, a metric now embraced as part of the California Title 24 building code and widely recognized as contributing to health and safety.
Traditional lighting audits focus on photometric values and traditional photometers are suitable for this purpose. Usually, these are basic lux meters are for illumination (i.e. lux level) verification. For luminance measurements a simple spot luminance meter with a fixed field-of-view is often used.
A more comprehensive approach to light quality verification requires the use of more advanced instruments such as illuminance spectrometers and imaging luminance meters in conjunction with analytical software. This combination is able to deliver both light quantity and quality metrics, information not available using a traditional photometric approach and lux meters.
Fig.2 Modern measurement instruments such as GL SPECTIS 1.0Touch + Flicker combine features of illuminance meter to measure lux levels with the capacity of specroradiometers to measure SPD. It provides a colorimetric evaluation together with light modulation i.e. Flicker metrics and the latest Circadian Lighting metrics included.
So why hasn’t the lighting community embraced more comprehensive lighting auditing methods? Two major obstacles have impeded progress, the accessibility of more advanced instruments/systems for field evaluations, and the fact these new metrics are not yet part of official international standards. Despite this, the industry and organizations such as the LRC or WELL are moving towards more advanced audit requirements with newly proposed metrics and qualities to verify the conformance of lighting installations. In parallel, mandatory building codes and regulations already include comprehensive requirements, but with no clearly defined means to measure or audit them.
The instrument accessibility issue is somewhat understandable. Reliable spectroradiometers are considerably more expensive than standard lux meters. Further, many lower-end instruments are not properly calibrated or are sufficiently accurate and repeatable for these more advanced applications.
III. NEW CONCEPT FOR ILLUMINANCE LIGHTING AUDITS
The lighting industry is rapidly evolving past the limitations of current lighting audit practices. Often times, even mandatory building requirements are not verified. A new approach is clearly needed. Certainly every lighting installation should be verified before it is commissioned. This requirement may be mandatory by code or law, or contractually required by the owner or builder. The goal of a new approach should be a closed-loop system that allows the specification, purchase, installation, verification and, if necessary, correction of the end result to match the initial requirements.
Any practical new approach must also recognize existing practices, tools and software, and build upon that infrastructure. For example, most lighting designers and engineers utilize CAD design software that can export the designed illuminance levels in a measurement grid. Further, the process should readily enable field audits, simplifying measurements, minimizing errors and supporting the subsequent preparation of comprehensive reports.
With these concepts in mind the GL Optic R&D team assigned software and hardware engineers to develop an illuminance auditing solution that closes the gap between the available sophisticated CAD design tools and real-life installations. The objectives of the project included:
- Single instrument to measure lux and other parameters
- Interface to communicate with CAD design software to obtain reference data
- Firmware supporting the onsite measurements process
- Reporting method to compare the measured values with the designed lighting levels
For the purposes of this limited development, only lux value verification was considered. Nevertheless, the concept is readily extensible as each measurement data file incorporates additional spectral characterizations that can be used for color and active radiation verification for specific applications like human centric lighting metrics or light flicker evaluations.
The workflow for this concept is described below. This particular implementation integrates with DIALux lighting design software. The principle is:
- Lighting design is made in DIALux and the measurement grid of points and designed illumination levels is exported from the CAD software as a layer.
- Layer is imported to GL Optic Spectrosoft software where verification points are selected , creating a list of points for the onsite verification process.
- The list is uploaded to the measurement device, a GL Optic SPECTIS 1.0Touch + Flicker (spectrometer and flicker meter, Figure 1).
- The on-site lighting audit is made point by point with the device, the operator directly observing on the screen each measured point and name/number, readily allowing cross-reference to the design plan.
- Once the measurements are made, the list of measured values is exported from the measuring device and imported to CAD software as an additional layer.
- The measured values are displayed next to the design values, simplifying verification and supporting report preparations.
This solution helps to avoid tedious measurements and error-prone manual field notes of lux values which then need to be reported somehow to the customer or contractor. Performing the lighting audit with prepared points displayed onboard the measuring device readily supports large building audits where hundreds of points need to be verified and a large volume of data must be accurately captured and analyzed
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CONCLUSIONS
As lighting technology and products continue their rapid evolution and deployment in our environments, and we simultaneous improve our ability to understand and measure their performance and impact upon us, new metrics and practical measurement systems are essential to assess them. This is particularly true for the “final mile” of measuring performance in the end-use, final installation environment.
The broader availability of comparatively lower cost, higher performance measurement instruments, couple with new analytical software provides hope that the gap between light-ing designs and implemented realities closes. Reliable measurements of lighting installations are possible with today’s technologies and will improve the quality of lighting while reducing energy consumption.
The future of closed-loop, end-to-end lighting quality audit and control systems is no longer limited to the laboratory. New standards are here today, are being more broadly adopted daily, and require more comprehensive lighting evaluations. In qualitative terms, new audits tools should allow us to provide the desired quantity and quality light wherever, whenever and however it is required.
REFERENCES
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[2] CIE S 025/E:2015 Test Method For Led Lamps, Led Luminaires and Led Modules
[3] IESNA LM-79-08 IES Approved Method for the Electrical and Photometric Measurements of Solid-State Lighting Products
[4] International WELL Building Institute, Well Building Standard V1, Q3 2017 addenda; Table L1, L2
[5] IESNA TM-30-15 IES Method for Evaluating Light Source Color Rendition
[6] California Title 24, Part 6 2016 Building Energy Efficiency Standards
[7] Rea et. al. “Circadian Light, Circadian Stimulus ”, J. Circadian Rhythms. 2010
[8] R.J. Lucas, S.N. Peirson, D.M. Berson, T.M. Brown, H.M. Cooper, et all Measuring and Using Light in the Melanopsin Age. 2014. Trends in Neuroscience, Volume 31, Issue 1, pp. 1-9.
[9] CIE TN 006:2016 Visual Aspects of Time-Modulated Lighting Systems
