Reading Time: 8 minutes
Harmonics and flicker testing exists not to validate product performance, but to ensure your device won’t compromise the integrity of the public power grid. For engineers used to thinking in terms of system efficiency and output specs, the requirements in IEC 61000-3-2 and IEC 61000-3-3 can come as a surprise, especially when devices that “work just fine” fail on the first attempt.
This post covers:
- When harmonics and flicker testing is required for certification;
- Common causes of failure and design factors that influence results; and
- What to expect during testing and how to plan for it early
Why Harmonics and Flicker Testing Is Required
Harmonics and flicker testing isn’t about how well a product performs, but how well it interacts with the power grid.
If a device draws power in short bursts or causes quick voltage drops, it can interfere with other equipment and disrupt power stability. That’s why regulators require devices to meet limits for current distortion and voltage fluctuations before they reach the market.
Key Required Standards
| Standard | What It Covers | When It Applies |
| IEC 61000-3-2 | Limits on harmonic current emissions | Equipment drawing ≤16 A per phase, connected to public low-voltage systems |
| IEC 61000-3-3 | Limits on voltage fluctuations and flicker | Equipment connected to low-voltage systems, especially lighting or devices with cycling loads |
These tests are mandatory for CE marking in the EU and frequently bundled into global EMC test plans.
Which Products Need Harmonics and Flicker Testing
Most AC-powered, RF-enabled devices fall into one of several IEC 61000-3-2 equipment classes. These classifications determine the harmonic current limits applied during testing. For engineers working on electronics with switching power supplies, LED drivers, or power factor correction, understanding the relevant class is essential before submitting a device for EMC evaluation.
RF-Enabled Device Classes (IEC 61000-3-2)
| Class | Typical Products | Relevance to Testing |
| Class A | Power supplies, base station subsystems, RF instrumentation | Harmonic distortion under load conditions; total harmonic current limits in the 2nd–40th range |
| Class C | LED drivers, connected luminaires, smart lighting platforms | Third-harmonic emissions, flicker during dimming, waveform distortion from constant current drivers |
| Class D | Consumer electronics ≥75 W: access points, displays, computing equipment | Nonlinear current draw, power factor correction behavior, load-dependent harmonics across modes |
These classes don’t reflect form factor or user function, but solely current waveform shape.
For example, a 60 W wall-powered IoT gateway with a switch-mode power supply and wireless transceiver might seem lightweight, but if it draws current in pulses and exhibits a crest factor over the limit, it can still fail testing under Class A. Similarly, a 100 W LED panel that dims via firmware will be held to Class C limits, and labs will test its waveform stability at multiple brightness levels.
Why Devices Fail Harmonics and Flicker Testing
Devices that perform well during in-house validation can still fail harmonics and flicker testing once they’re connected to standardized test equipment. Failures are usually rooted in how the device draws current from the mains, especially during startup, load changes, or power-conversion stages.
Common Failure Triggers
Non-linear current draw
Most RF and embedded systems use switch-mode power supplies (SMPS) that draw current in short bursts. Without adequate input filtering or passive correction, this leads to significant harmonic distortion. The 3rd, 5th, and 7th harmonics are usually the highest contributors. Class A and D devices often fail here when load current varies between modes or during idle-to-active transitions.
Undercorrected PFC behavior
Devices above 75 W are expected to include power factor correction (PFC). However, poorly implemented PFC, particularly at the firmware or controller level, can introduce low-order harmonics and increase crest factor, pushing emissions past the acceptable range. This is especially common in variable-load devices or equipment that ramps output in discrete steps.
Inrush current during startup
Capacitor charging, relay activation, or bulk DC stages at power-on can create short-duration spikes in current. These spikes may exceed harmonic current limits for their duration, even if the steady-state behavior is compliant. This type of issue is often missed in early-stage design reviews because it’s transient and not easily captured without dedicated equipment.
Power-state transitions in connected systems
Embedded RF systems often change operating states in response to network activity, signal strength, or firmware control. These transitions, such as waking a radio, ramping a power amplifier, or activating an internal subsystem, can produce rapid current steps or change the shape of the input waveform. Even if the average power remains within specification, these transitions can trigger harmonics or flicker violations when captured in a compliance test environment.
What to Expect During Testing
Harmonics and flicker testing is performed in a controlled environment that replicates standardized grid conditions. Labs use fixed reference impedances, regulated voltage, and calibrated measurement tools to capture current waveform behavior under repeatable scenarios.
Core Testing Elements
- Stabilized AC source simulates the low-voltage public mains;
- Harmonic analyzer captures current distortion up to the 40th harmonic; and
- Flickermeter calculates short- and long-term flicker severity (Pst and Plt)
Devices are evaluated in multiple operating modes, including full load, power-up, and dimmed or reduced-power states. For switching systems or digitally controlled power supplies, harmonic content is measured across transitions, not just at steady state.
Regional Variations and Overlap
Although harmonics and flicker testing is most closely associated with the European Union’s CE marking requirements, the same core standards are referenced or accepted in several other markets.
| Region | Primary Standard | Notes |
| European Union | IEC 61000-3-2 / 3-3 | Mandatory for CE Marking |
| United Kingdom | EN standards (based on IEC) | Fully aligned with EU |
| Australia / New Zealand | AS/NZS 61000.3.2 / 3.3 | Identical test parameters and limits |
| South Korea | KN standards (based on IEC) | IEC-compliant but may require documentation in Korean |
| Japan | JIS C 61000-3-2 / 3-3 | Aligned in limits, with additional administrative requirements |
Because of this overlap, many experienced labs can leverage a single harmonics and flicker test campaign across multiple target markets, so long as the product is classified and tested correctly the first time. Misclassification or failure to capture edge-case load behavior can lead to retesting, even across harmonized regions.
Devices with multiple regional variants (e.g., voltage-selectable power supplies) should define input configurations clearly up front. This allows the lab to structure the test plan to cover all necessary conditions without repeating entire sequences unnecessarily.
Design Decisions That Affect Test Outcomes
Many harmonics and flicker failures can be traced back to design-stage tradeoffs, particularly in power architecture, firmware-controlled load behavior, or PFC implementation. Below are common choices that can impact testing results:
Input Stage Architecture
Switch-mode power supplies (SMPS) are nearly universal in RF-enabled devices. They’re compact and efficient, but they also generate non-linear current waveforms. Without adequate input filtering or staged soft-start control, the result is high harmonic distortion, often in the 3rd and 5th harmonic bands. Adding bulk capacitance or LC filters can help, but these introduce other tradeoffs in EMI and radiated emissions.
Designers working on systems with internal radios should consider how LC filters and input capacitance affect both harmonic distortion and conducted EMI, especially when switching regulators operate near RF bands.
Power Factor Correction (PFC)
For products above 75 W, active PFC is not optional. But poor PFC implementation is a frequent cause of failure in Class D devices. Control loop overshoot, inconsistent response during load transitions, or narrow-band distortion from digital PFC controllers can all push harmonic levels beyond acceptable limits, even if the average power factor appears within spec.
Load Modulation and Firmware Control
RF-connected devices frequently cycle subsystems on and off based on signal activity, user input, or thermal events. These transitions may be invisible from a functionality standpoint, but they often produce measurable flicker or step-changes in input current.
Wrapping Up
Harmonics and flicker testing isn’t just a checkbox, it’s a critical step in verifying that a device will operate safely and predictably on public power systems. Engineers working on RF-connected devices need to account for current distortion, power stage behavior, and load transitions early in the design process to avoid delays at the compliance stage. When approached strategically, these tests become an extension of the product’s overall EMC design workflow.
At MiCOM Labs, we look forward to partnering with RF device manufacturers who require harmonics and flicker testing, especially as part of a complete EMC and regulatory certification plan.