A new report prepared by the Pacific Northwest National Laboratory for the U.S. Department of Energy focuses on a topic to which energy managers and building planners must pay attention: Flicker.
All light sources modulate their intensity. Generally, this process – which is informally called flicker -- is invisible. But it has a big impact and should be a key area of research in facilities being built or those in which a lighting change is being considered. The amount and nature of flicker has a direct impact on people in the building, according to Tess Perris, a Lighting Scientist at the lab. “Research has shown that flicker from light sources is related to migraines, headaches, reduced visual performance and a lot of neurological issues,” she said.
The lab tested three flicker meters: The Admesy Amsteria (SC-ASTR-01), Gigahertz-Optik’s BTS256-EF and the EVERFINE LFA-2000. The three, which were chosen because they are hand held or small enough to be used in the field, were assessed on the ability to measure flicker in LEDs, ceramic metal halide (CML), halogen, compact fluorescent and florescent lights.
Characterizing flicker is more important than ever: The ascendency of LEDs means that there is a tremendous amount of lighting retrofit activity. Related to that is the long lifetime of LEDs. With lifetimes measured in decades, making the right decision is even more important than in the past.
It also is important to recognize that LEDs have unique characteristics. “LEDs are not necessarily more or less dangerous, but they have more variation in performance, so accurately characterizing performance is more important than more convention light sources, where they isn’t as much variation,” she said. “If you look at the light output waveform and how the LED performs over 100 millisecond, for example, you see significant variation in the shape of the waveform. It is not always a sine curve. It depends on the pairing of the LED and the driver. There are many different parts of the LED that can cause a difference.”
Perrin said that other meters are on the market. They didn't, however, meet the specifications for this particular test. The report found no dramatic difference between the meters that were tested:
The results and analysis show that the three commercially available flicker meters evaluated for this study measured light-intensity waveforms and calculated essential flicker-performance characteristics and metrics similarly, both to each other and to the reference meter chosen as an accuracy benchmark.
The report offers several recommendations that provide some basics on how best to characterize flicker. Perrin suggests that those in charge of lighting buying decisions take the matter seriously: “The first thing is to get them in and mock up them up to see how they perform at full output and at different dimming level. Test them on whatever controls you have.”
This is a tricky area. The business side is ahead of the technology. Efforts to characterize flicker are just gaining steam, but buying decisions are being made today. Perrin said that it is a good idea to look for products that accept software upgrades and can become more effectively as flicker measurement technology evolves.
States – particularly California – and organizations such as the IEEE, the International Commission on Illumination and the National Institute of Standards and Technology (NIST) -- are looking more closely at flicker. Best practices exist. The best practices will be refined and actual standards likely will emerge. In that landscape, meters that can be tweaked to offer higher sampling rates – and thereby higher resolution waveforms – are recommended.
