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Flicker Free LED Lighting

When choosing an LED light, do you consider how flicker will affect your application? If not, please take a moment to learn about flicker and how it can impact your lighting environment.

What is Flicker and it’s Effect?

Flicker is the rapid variation in light intensity over time. Flicker may be visible, or imperceptible, depending on the intensity and speed of the variations.
Visible flicker is detected by the eye and consciously registered by our brains. Invisible flicker cannot be directly perceived by the human eye; however, we may still sense it. People who are sensitive to flicker may be unaware that their discomfort is caused by flickering light.
Although flicker in lighting is often not directly perceived by the human eye, it still causes problems such as eyestrain, headaches after prolonged exposure, more severe problems for sensitive people (e.g. seizures), distortion in video recording, interference with the operation of technical equipment (e.g. bar code scanners) etc. IEEE Std 1789-2015 explained more details and studies about the biological effects caused by flicker. [1]

Flicker in Various Applications

For both general lighting and task lighting, lamps with reduced flicker are always preferable. Minimizing flicker is especially important where sensitive populations spend time, like hospitals, daycare centers, assisted living facilities, and classrooms. It is also recommended in areas where certain tasks or operations need to be performed safely and accurately, such as labs, warehouses, and industrial spaces. In the cases of video conferencing and laboratory video documentation, flicker free lighting is important to eliminate unwanted artifacts in the image capture and transmission. In offices and working environments, reduced flicker may lead to greater focus and higher productivity. Flicker free lighting may help students retain lessons by promoting concentration. In industrial working environments, flicker-free LED lights eliminate the strobing effect, reducing dangers around high-speed machinery. In warehouses, reduced flicker ensures sensitive scanning equipment operates without disruption. Refer to IEEE Std 1789-2015 for more information regarding published research and/or Expert Opinion that identified the above mentioned major and minor adverse effects of flicker.[1]
Flicker in your lighting environment matters more than you may think. Choosing an LED with less flicker will improve performance in almost any lighting solution.

Flicker in LED Lighting

Unlike other lighting sources such as incandescent lamps which will not stop glowing right after the lamps switched off, LEDs respond immediately to the supply of current. In the US, electricity is delivered via alternating current (AC) at a frequency of 60Hz. The voltage supplied to a lighting source bounces rapidly between “on” and “off” in a sine waveform. As a result, the LED light source will be driven to produce alternating light output, or flicker, at a frequency of 120Hz, twice that of the power grid’s frequency. This is why most LED lights come with their own electronic circuitry: an LED driver. Quality driver in superior system design regulates the current and ensures that LEDs produce a constant state of light. While inferior driver design cannot guarantee the system performance and allow flicker.

Flicker Metrics

Two simple and common metrics used to measure flicker are Percent Flicker (PF), also known as modulation depth, and Flicker Index (FI).

Percent Flicker (PF) is a commonly used method for quantifying flicker as a percentage. It refers to the amount of flicker at a given frequency, also known as peak-to-peak contrast.

Flicker Index (FI) is defined as the area above the line of average light divided by the total area of the light output curve for a single cycle.

Measuring flicker2

However, Percent Flicker or Flicker Index alone does not determine whether you will perceive the flicker effect from a lighting system. Flicker frequency—the rate at which the light output fluctuates at a given time—also determines whether flicker is observed or sensed.

For most people, flicker at a frequency of less than 80Hz is perceptible. When the frequency is higher than 80Hz it is usually unnoticeable, thus becoming invisible flicker, and may cause a stroboscopic effect for objects moving at a high speed.

IEEE (The Institute of Electrical and Electronics Engineers), outlines the various risk levels associated with flicker frequency and sets a standard for acceptable ranges in IEEE P1789. As shown here in the graph, the green region represents “no observable effect” while the yellow region represents a low risk of health effects due to flicker.

Flicker Metrics

In addition to Percent Flicker and Flicker Index there are additional metrics to communicate more information. See below table for a quick overview and comparison.

Flicker Metric


Introduced by

Adopted by

Acceptance Criteria

Pros & Cons

Percent Flicker(PF)
0-100%, the lower the less substantial

A relative measure of the cyclic variation in the amplitude of a light.

Illuminating Engineering Society (IES)

IEEE Standard 1789

Divides light modulation vs. frequency (1-2000Hz) into areas: “No effect”, “low risk"

Easy to understand and calculate.
More well-known and more commonly used.
Assumes periodic waveform.
Does not account for frequency, wave shape and duty cycle.
No relation to human perception.

California Title 24 requirements

<30% at frequencies less than 200Hz

Energy Star

Report only

Flicker Index (FI)
0-1, the lower the less substantial

A measure of the cyclic variation in output of a light source taking into account the waveform of the light output.

Illuminating Engineering Society (IES)

Energy Star

Report only

Easy to understand.
Assumes periodic waveform.
Does not account for frequency.
No relation to human perception.
Less well-known and rarely used.

Stroboscopic Visibility Measure (SVM)
SVM <= 1.0, visibility threshold

Time domain → frequency domain.
Summation of weighted Fourier components.

PHILIPS & CIE [2] [6]

NEMA 77 [5]


Based on human perception trials.
Measures primarily stroboscopic effects >80Hz for moving objects, not static flicker.
Account for variations in waveform frequency.
Less conservative than IEEE 1789 Standard.
Not yet well known or widely used in industry.

Energy Star

Report only

Short Term Flicker Indicator (Pst)
Pst <= 1.0, visibility threshold

The flicker severity evaluated over a short period (minutes).

IEC/TR 61547-1 [3]



Quantify visible flicker <80Hz.
Well established and used by IEC for many years.
Complex and originally developed to quantify power line quality.

Energy Star

Report only

ASSIST Flicker Perception (MP)
Mp <= 1.0, visibility threshold

An objective method to assess the perception of flicker directly observed from light sources recommended by ASSIST.

RPI LRC Assist [4]

Energy Star

Report only

Similar to Pst in terms of values and dependence on frequency.
Accounts for wave shape and frequency.
Based off of (limited) human perception trials.
Focuses on perceptible flicker: <100Hz.
Complex measurement and analysis.

Regulating Flicker in LED Lighting

LED flicker is generally caused by inferior driver designs. For dimming products, the incompatibility between LED products and the existing dimming systems can also cause flickering result.

In order to avoid flicker after installation of any LED lighting products in your project, it is worthwhile to check whether your LED lighting manufacturer offers flicker-free products. In case of dimming needed, you should also check the dimmer compatibility list published by most manufactures to ensure your existing dimming systems are compatible with the new products before installation.

Flicker free LED lamps from GREEN CREATIVE are designed with proprietary LED driver for eliminating flicker effect and ensure quality lighting result for various applications.

GREEN CREATIVE Flicker-free products: Percent Flicker ≤5% at frequencies less than 200Hz
GREEN CREATIVE Low-flicker products: Percent Flicker <30% at frequencies less than 200Hz


[1] IEEE Std 1789-2015 – IEEE Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers. Available at http://standards.ieee.org/findstds/standard/1789-2015.html.
[2] CIE TN 006:2016, Visual Aspects of Time-Modulated Lighting Systems – Definitions and Measurement Models. Available at http://files.cie.co.at/883_CIE_TN_006-2016.pdf
[3] IEC 2015. IEC TR 61547-1:2015 Equipment for General Lighting Purposes - EMC Immunity Requirements - Part 1: An Objective Voltage Fluctuation Immunity Test Method.
[4] The Alliance for Solid-State Illumination Systems and Technologies (ASSIST) Program. https://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-FlickerMetric.pdf.
[5] NEMA 77-2017, Temporal Light Artifacts: Test Methods and Guidance for Acceptance Criteria. Available at https://www.nema.org/Standards/Pages/Temporal-Light-Artifacts-Test-Methods-and-Guidance-for-Acceptance-Criteria.aspx.
[6] CIE TN 008:2017, Final Report CIE Stakeholder Workshop for Temporal Light Modulation Standards for Lighting Systems. Available at http://www.cie.co.at/publications/final-report-cie-stakeholder-workshop-temporal-light-modulation-standards-lighting.