Since my first article on the PQ phenomenon called flicker in 1998, the benefits of using a new methodology to determine it have been promoted.

Having been involved in the IEEE 1453 working group since its inception, there was a significant push to educate electrical contractors, field service technicians, facility managers and electric utility engineers on the parameters P_st (perceptibility short-term) and P_lt (perceptibility long-term) as a means of evaluating if there is a flicker problem. A P_st reading greater than 1 was a problem for most people. It seemed like a simple answer to a complex problem. But recent developments in lighting technologies have raised significant issues with that methodology.

Flicker is technically described in the standards as voltage fluctuations that result in modulation of the light amplitude or output from luminaries (or bulbs). Depending on the frequency and amplitude of the modulation, it can potentially cause nausea or headaches, or even trigger epileptic seizures. As little as 0.25% modulation of the voltage at 8.8 Hz is noticeable with incandescent bulbs.

Quantizing flicker-causing fluctuations

The first effort to quantize these flicker-causing fluctuations was known as the GE flicker curve, which was published by General Electric based on numerous studies from the 1930s. IEEE Std 141-1976 included it, followed by IEEE Std 519-1992. However, it was not an easy process to determine the validity and source of customer complaints of lights flickering.

Based on work in UIE 868 and subsequently in IEC 61000-15, the concept to take a very complex set of mathematical operations into a single parameter evolved. It was based on a 60W incandescent bulb’s response to subharmonic frequencies modulating the 230V, 50 Hz power frequency used in Europe. 

When IEEE 1453-2004 adopted this methodology, it required modifications to the algorithms to work with 60W incandescent bulbs at 120V, 60 Hz. So began the quest to educate the world, at least those willing to listen.

Manufacturers integrating the methodology into their PQ instruments found it took considerable processing power to do so. Different interpretations of the standard’s algorithms led to distinct results from a set of test signals, causing more reluctance to accept this method. Attempts to “certify” compliance led to more standards.

Incandescent, fluorescent, CFL, LED

The IEEE 1453 standard has since evolved into an emission limits and planning limits practice for electric utilities, rather than those dealing with complaints behind the meter. The parameter did work in most cases, but it was only accurate for incandescent bulbs. Fluorescent lighting needed a different set of weighting filters. Along came CFL and LED lamps and other modern lightning technologies, including dimmers. Studies as early as 2013 concluded that lighting technologies differ in flicker performance, and the unpredictability has only gotten worse. 

The increase in interharmonics in electrical systems further complicates the problem. For interharmonics at frequencies higher than 100 Hz, interharmonics of amplitudes around 0.5% is enough to produce P_st = 1.15.

With sales of new incandescent bulbs now prohibited in the United States (except in special cases), more LED replacement and new construction fixtures are out there. Many electricians have seen an increase in customer complaints of flickering LED lights on dimmer switches, even where they are rated for LEDs. A flickermeter and its algorithms deal with an array of dimmer technologies in several ways, including:

• Forward phase: Usually uses a TRIAC dimmer that phase cuts the leading edge of the AC sine wave.
• Reverse phase: Usually requires using a neutral wire and uses a MOSFET dimmer that phase cuts the trailing edge of the AC sine wave.
• 0–10V: Uses a dedicated 0–10V DC voltage signal for control.
• DMX: Digital multiplexing (DMX) is a digital communication of individual fixtures using a low-voltage control signal.
• DALI: Digital Addressable Lighting Interface (DALI) is a two-way digital lighting control system protocol.

What happens when the light source flickers even when there is no voltage fluctuation? That doesn’t meet the aforementioned definition of flicker, yet customers complain. In many of these cases, a failure within the LED light is causing the flicker. 

Now there is a new one—shadow flicker. Fortunately, it’s limited to few locations so far. Shadow flicker is the effect of the sun (low on the horizon) shining through the rotating blades of a wind turbine, casting a moving shadow across a building or residential structure. This creates the perception of a repeating flicker of alternating light and dark periods through windows.

Has the flickermeter and its simple P_st parameter become obsolete before it gained wide acceptance and use? Perhaps the idea proposed a couple decades ago should be reconsidered. What really matters to the end-user is that the light output is flickering. Why not just directly measure that? Or does its perception also vary if it is a 2,700K or 4,000K LED light?

stock.adobe.com / rvika