Why Do LED Lights Flicker In Slow Motion Videos The Science Behind The Effect

When you record a scene under LED lighting with your smartphone or camera in slow-motion mode, you might notice an odd visual artifact: flickering bands, pulsing light, or dark rolling lines across the frame. This phenomenon is not a defect in your device or the bulbs themselves—it’s a clash between two invisible rhythms: the frequency of the LED’s power supply and the timing of your camera’s sensor. Understanding why this happens reveals a fascinating intersection of physics, electronics, and digital imaging.

LED lights are energy-efficient and long-lasting, making them dominant in homes, studios, and streetlights. But their behavior differs from traditional incandescent bulbs, especially when captured at high frame rates. The flicker seen in slow-motion videos isn’t always visible to the naked eye, yet it becomes glaringly apparent on screen. This article explores the technical roots of this effect, explains how cameras interact with artificial lighting, and offers practical solutions for creators and consumers alike.

The Basics of LED Operation and Power Supply

Unlike incandescent bulbs, which produce light by heating a filament until it glows, LEDs (Light Emitting Diodes) generate light through electroluminescence—a process where electrons recombine with electron holes within a semiconductor, releasing photons. While efficient, this method depends heavily on the quality and type of electrical current supplied.

Most household electricity is alternating current (AC), which oscillates at 50 Hz or 60 Hz depending on the region. When AC power reaches an LED bulb, internal drivers convert it to direct current (DC). However, many low-cost or non-dimmable LED drivers don't smooth out the current completely. As a result, the LED still experiences rapid fluctuations in brightness—turning on and off hundreds of times per second.

This flickering occurs at twice the AC frequency due to rectification: 100 Hz in 50 Hz countries and 120 Hz in 60 Hz regions. Though too fast for human eyes to detect, these micro-cycles create a strobing effect that cameras can capture under certain conditions.

Tip: Use high-frequency LED drivers or DC-powered LEDs for video production to minimize flicker.

How Cameras Capture Light: Frame Rate and Shutter Speed

A camera records video by capturing a sequence of still images—frames—per second. Standard video runs at 24, 30, or 60 frames per second (fps). Slow-motion video, however, uses much higher frame rates—120, 240, or even 960 fps—to stretch time visually.

Each frame is exposed for a specific duration determined by the shutter speed. For example, at 1/120th of a second shutter speed, each frame captures light over approximately 8.3 milliseconds. If the LED flickers during that window, the amount of light hitting the sensor varies from one frame to the next.

When played back in slow motion, these tiny variations in brightness become exaggerated. What was imperceptible in real time appears as rhythmic pulsing, banding, or strobing across the image. This mismatch between the LED’s flicker frequency and the camera’s sampling rate creates the illusion of instability.

“Flicker in slow-motion footage is not about the LED failing—it's about synchronization. It’s a sampling problem, not a lighting problem.” — Dr. Lena Torres, Imaging Scientist at MIT Media Lab

The Rolling Shutter Effect and Banding Patterns

Many modern cameras, especially smartphones and mirrorless models, use CMOS sensors with a rolling shutter mechanism. Instead of capturing the entire frame at once, the sensor scans the scene line by line—from top to bottom—over a few milliseconds.

If an LED flickers while the sensor is scanning, different parts of the image are exposed at slightly different moments in the light cycle. This results in visible horizontal bands: bright sections where the LED was “on,” and dark ones where it was “off.” These bands move upward or downward depending on the phase relationship between the flicker and scan speed.

The effect intensifies in slow-motion because higher frame rates often require faster shutter speeds. A shutter speed of 1/1000th of a second may only capture a fraction of a single flicker cycle, increasing the chance of uneven exposure across frames and within individual frames.

Example Scenario: Concert Footage Gone Wrong

Imagine filming a live music performance indoors using stage lighting powered by standard LED panels. The room appears evenly lit to your eyes. You switch your phone to 240 fps to capture dramatic slow-motion clips of the drummer. Upon playback, you notice dark bars sweeping across the screen every few frames, distorting the visuals.

This isn’t a glitch. The stage LEDs are likely running on 120 Hz modulation, and your camera’s 1/1000s shutter speed is sampling inconsistent brightness levels. Because the rolling shutter reads the sensor progressively, and the LEDs pulse rapidly, the timing misalignment produces moving shadows. Without understanding the cause, it’s easy to blame the camera—but the truth lies in the interaction between light and sensor.

Factors That Influence Flicker Visibility

Not all LED lights flicker equally, nor do all cameras reveal it the same way. Several variables determine whether flicker will appear in slow-motion recordings:

• Driver Quality: Cheap LED bulbs often use basic rectifier circuits without adequate filtering, leading to pronounced flicker. High-end fixtures use constant-current drivers that maintain steady output.
• Dimming Method: Phase-cut dimming (common in TRIAC-based systems) can increase flicker by chopping parts of the AC waveform. PWM (Pulse Width Modulation) dimming at low frequencies also introduces visible cycles.
• Camera Frame Rate: Recording at 60 fps under 60 Hz mains power may align well, but 120 fps doubles the risk of mismatch. Mismatched frequencies amplify perceived flicker.
• Shutter Angle/Speed: Cinematic cameras use shutter angles (e.g., 180° rule = 1/48s at 24 fps). Deviating from this increases flicker sensitivity.
• Power Source Stability: Voltage fluctuations or dirty power can worsen flicker, especially in industrial environments.

Do’s and Don’ts When Filming Under LED Lighting

Action	Recommended?	Reason
Use 120 fps in 60 Hz countries	No	Risk of resonance with 120 Hz flicker; try 100 fps instead
Select high-CRI, studio-grade LEDs	Yes	Better drivers reduce flicker and improve color accuracy
Shoot with very fast shutter speeds	Careful	Faster than 1/flicker-frequency increases flicker visibility
Use manual white balance	Yes	Auto WB can shift colors due to flicker-induced chrominance changes
Record under sunlight or incandescent lights	Yes	Thermal sources emit continuous light with no flicker

Solutions and Best Practices for Creators

Whether you're a filmmaker, content creator, or casual videographer, avoiding LED flicker in slow-motion requires awareness and planning. Here’s a step-by-step guide to minimize or eliminate the issue:

1. Test Before Shooting: Record a short clip in your intended slow-motion setting. Play it back immediately to check for flicker or banding.
2. Adjust Frame Rate: Match your camera’s frame rate to the local power frequency. In 60 Hz regions, use 60, 120, or 240 fps cautiously; consider 100 or 150 fps if available. In 50 Hz areas, 100 or 200 fps may work better than 120.
3. Modify Shutter Speed: Follow the 180° shutter rule when possible. At 120 fps, use 1/240s—not 1/1000s. Slower shutter speeds average out flicker over time.
4. Choose Flicker-Free Lights: Look for specifications like “flicker-free,” “DC-driven,” or “high-frequency PWM” (>20 kHz). Brands like Aputure, Nanlite, and ARRI offer professional-grade options.
5. Use External Power: Battery-powered LEDs often run on stable DC, eliminating AC-related ripple entirely.
6. Enable Anti-Flicker Settings: Some cameras (e.g., Sony Alpha series, Panasonic GH5) have built-in anti-flicker modes that detect ambient light frequency and adjust timing automatically.
7. Edit in Post (Limited Fix): Software like DaVinci Resolve or Adobe Premiere Pro includes temporal noise reduction tools that can soften flicker, though they can’t fully restore lost data.

Tip: When in doubt, shoot test footage at multiple frame rates and review on a calibrated monitor.

Checklist: Pre-Shoot LED Flicker Prevention

• ☐ Confirm local mains frequency (50 Hz or 60 Hz)
• ☐ Choose lights labeled “flicker-free” or “film-grade”
• ☐ Avoid cheap LED bulbs or unbranded strips
• ☐ Set camera to match power frequency (e.g., 50/100/200 fps or 60/120/240 fps)
• ☐ Use shutter speed close to 1/(2×frame rate)
• ☐ Enable camera anti-flicker mode if available
• ☐ Conduct a 10-second slow-motion test and inspect playback

FAQ: Common Questions About LED Flicker in Video

Can I see LED flicker with my eyes?

Most people cannot perceive LED flicker above 70–90 Hz, though some are more sensitive, especially in peripheral vision. Prolonged exposure to flickering LEDs may cause eye strain or headaches in susceptible individuals, even if the flicker isn’t consciously noticed.

Why don’t incandescent bulbs flicker in videos?

Incandescent bulbs heat a filament that remains hot between AC cycles, acting as a natural low-pass filter. Even though the power supply fluctuates, the thermal inertia of the filament smooths out brightness changes, resulting in nearly continuous light emission.

Does flicker affect photo quality too?

Yes. With fast shutter speeds (e.g., 1/1000s), still photos taken under flickering LEDs can show uneven exposure or color casts, particularly in burst mode. This is common in sports photography under indoor arenas lit with LEDs.

Conclusion: Mastering Light and Motion

The flicker of LED lights in slow-motion videos is a product of modern technology meeting physical limits. It’s not a flaw, but a reminder that what we see and what cameras record are governed by different rules. By understanding the interplay between electrical frequency, driver design, and sensor mechanics, you gain control over your visual storytelling.

Whether you’re filming a wedding, a product demo, or a TikTok dance, clean, flicker-free footage reflects professionalism and attention to detail. The solutions aren’t complicated—better lights, smarter settings, and a bit of pre-planning go a long way. As LED technology continues to evolve, so do the tools to manage its quirks. Stay informed, test rigorously, and shoot with confidence.

🚀 Ready to shoot flicker-free slow motion? Audit your current lighting setup, run a quick test, and share your results with others facing the same challenge. Knowledge shared is clarity gained.