As national and global interest in the “flicker” effect from indoor lighting grows, researchers at PNNL have evaluated eight hand-held flicker measurement devices. PNNL’s work is helping to establish future device measurement procedures, metrics, and performance criteria, which ultimately could lead to improved lighting methods.
Flicker, more formally referred to as temporal light modulation, is a repetitive change in light output over time. It can have different potential effects and names depending on how frequently it varies, the shape of the waveform, and what’s moving (either the objects or the eyes).
Some forms of flicker are a serious concern. The U.S. Department of Energy (DOE), as well as standards organizations worldwide, is spending time, effort, and research dollars on the subject. There’s increasing awareness that flicker may negatively impact human productivity and safety in the workplace and other settings, and cause health issues. Fortunately, serious flicker in LED products is uncommon, but somewhere between 10 and 25 percent of the population is sensitive to flicker, and the few products that flicker badly may contribute to headaches, migraines, distraction, or malaise.
It’s anticipated that such concerns will prompt a wide range of users—from lighting manufacturers to building managers and lighting specifiers, architects, and engineers—to seek out effective and convenient hand-held meters that identify and measure variations in light output from lighting systems. “Ultimately, these measurement tools will enable characterization of lighting in a certain space and help to determine whether the level of flicker is acceptable for a given application,” says PNNL’s Felipe Leon, an electrical engineer.
A Spotlight on Capabilities
In 2017, funded by DOE, Leon and PNNL colleagues embarked upon a comprehensive evaluation of a group of hand-held flicker measurement devices available in the marketplace at the time. The eight meters ranged from a simple smart phone application that employs the phone’s camera to capture light, to scientific-grade units. The meters offered varying features and levels of capability, which were factored into the evaluation process and results.
The researchers employed PNNL’s Lighting Metrology Laboratory, specifically the lab’s two-meter-diameter integrating sphere, to conduct evaluations. The sphere delivered light from 12 different sources (LED and compact fluorescent bulbs, troffer fixtures, etc.), individually, to each hand-held device. For comparison purposes, a laboratory benchtop meter, which had undergone previous testing and validation, served as the reference tool and was positioned in the sphere adjacent to the hand-held device.
The PNNL study concluded that for some flicker measurements, hand-held units today are capable of providing performance nearing that of a quality benchtop meter in a controlled environment. The one area where the units were less reliable was in measuring the flicker frequency, an important component when evaluating flicker performance against current standards. The PNNL researchers emphasize that some of these devices should be used as mere indicators of a potential problem, to be further investigated by more precise flicker measuring equipment, hand-held or benchtop, for confirmation.
Although the study uncovered some limitations and anomalies with the hand-held meters, the researchers said most issues have since been addressed by manufacturers, either in product literature, on the device/software itself, or through firmware/software updates.
The research team concluded that device users would need to put some thought into whether a given hand-held tool would meet their expectations, particularly related to measurement reliability, versatility, and data collection and use.
"We all want to eradicate flicker from LED lighting systems, and even though only a small percentage of products flicker, it’s a rising concern,” says Naomi Miller, a social scientist at PNNL and research team member. “But you can’t set standards for flicker until you can reliably measure it, and that’s why this testing of hand-held meters is so important.”
The team’s findings are captured in the report, “Characterizing Photometric Flicker – Handheld Meters,” issued in November 2018.