Motion bars, those frustrating dark bands that scroll across your video when filming indoors, are primarily caused by a mismatch between your camera’s shutter speed and the refresh rate of artificial lighting. Most indoor lighting, especially fluorescent and LED lights, flicker at a frequency of either 50Hz or 60Hz, corresponding to the electrical current in your region. If your shutter speed is faster than the lighting cycle, your camera will capture these subtle flickers, resulting in the visible bars.
Understanding the Problem: Shutter Speed and Lighting
The phenomenon often referred to as motion bars or rolling bars is a type of video artifact. It arises from the way digital cameras capture images and how artificial lighting behaves.
The Role of Shutter Speed
Shutter speed refers to the amount of time your camera’s sensor is exposed to light. A fast shutter speed captures a “snapshot” of a moment, while a slow shutter speed allows more light to enter, resulting in motion blur if the subject moves. When filming indoors under artificial lights, a fast shutter speed can be problematic.
The Nature of Artificial Lighting
Most indoor lights, including fluorescent and LED, don’t emit a constant, steady stream of light. Instead, they flicker on and off very rapidly, following the alternating current (AC) frequency. This flicker is usually imperceptible to the human eye, but a camera’s sensor can detect it. The refresh rate of this flickering varies depending on the region: 50Hz in most of Europe and parts of Asia, and 60Hz in North America.
The Mismatch Explained
When your camera’s shutter speed is faster than the rate at which the lights are flickering, it captures moments when the light is both on and off. This creates the alternating dark and light bands we see as motion bars. These bars appear to “roll” up or down the screen because the flickering isn’t perfectly synchronized with the camera’s scanning process.
How to Eliminate Motion Bars
Fortunately, there are several techniques you can employ to eliminate or minimize the appearance of motion bars when filming indoors.
Adjusting Shutter Speed
The simplest solution is to adjust your shutter speed to match the refresh rate of your local electricity. For 60Hz regions, a shutter speed of 1/60th of a second or slower is often effective. For 50Hz regions, use 1/50th of a second or slower. Experimenting with slightly slower shutter speeds, like 1/30th of a second, may also yield better results.
Utilizing Anti-Flicker Settings
Many modern cameras have built-in anti-flicker settings specifically designed to address this issue. These settings automatically adjust the shutter speed to synchronize with the local electrical frequency. Check your camera’s menu for options labeled “Anti-Flicker,” “Flicker Reduction,” or similar terms, and enable them.
Switching to Incandescent or Natural Light
Incandescent lights and natural sunlight emit a continuous spectrum of light without the flickering issues of fluorescent and LED lights. If possible, switch to incandescent bulbs or position your subject near a window to utilize natural light. Be aware of color temperature differences; natural light is generally “cooler” than indoor lighting.
Using Professional Lighting
Professional video lighting kits often include lights with specialized ballasts or drivers designed to minimize flickering. These lights are more expensive but provide a consistent and stable light source for high-quality video production.
Editing Software
Although prevention is ideal, editing software can sometimes mitigate motion bars. Some video editing programs offer filters or effects specifically designed to reduce or eliminate flicker. However, this is often a last resort, as it can negatively impact the overall image quality.
Frequently Asked Questions (FAQs)
Here are some common questions and detailed answers regarding motion bars and how to avoid them.
FAQ 1: Why don’t I see motion bars with my eyes?
Your brain and eyes are far more adept at processing and compensating for flicker than a digital camera sensor. The flicker rate is typically too fast for you to consciously perceive it.
FAQ 2: Does the frame rate of my video affect motion bars?
Yes, the frame rate interacts with the shutter speed. For example, if you’re shooting at 30 frames per second (fps) and using a shutter speed of 1/60th of a second, you’re essentially capturing each frame for half the time it takes to display it, which can help minimize flicker.
FAQ 3: Will changing the ISO help reduce motion bars?
No, ISO (sensitivity to light) does not directly affect motion bars. While adjusting ISO can make your image brighter or darker, it won’t address the underlying issue of shutter speed mismatch.
FAQ 4: Does using a higher-quality camera eliminate motion bars?
A higher-quality camera might have more sophisticated anti-flicker settings and better image processing, which can help mitigate the problem. However, even high-end cameras can be affected by motion bars if the shutter speed is not properly adjusted.
FAQ 5: Are motion bars more common with certain types of lights?
Yes, fluorescent lights, particularly older models, are notorious for causing motion bars. LED lights can also cause problems, although newer, higher-quality LEDs are generally better at minimizing flicker. Incandescent lights, as mentioned, are less likely to cause the issue.
FAQ 6: Can motion bars be completely removed in post-production?
While some video editing software offers tools to reduce flicker, complete removal is often difficult and can negatively affect image quality. It’s much better to prevent motion bars during filming.
FAQ 7: What if I need a fast shutter speed indoors?
If you absolutely need a fast shutter speed, consider increasing the intensity of your lighting. Using brighter, flicker-free lights can allow you to use a faster shutter speed without introducing motion bars.
FAQ 8: How can I determine the refresh rate of the electricity in my region?
Typically, North America (including the US and Canada) uses 60Hz, while most of Europe and parts of Asia use 50Hz. You can easily find this information by searching online for “electricity frequency [your country].”
FAQ 9: Is there an app that can detect the light flicker rate?
Yes, there are smartphone apps designed to measure the flicker rate of lights. These apps can be helpful in identifying problematic lighting and determining the appropriate shutter speed.
FAQ 10: Does recording in slow motion exacerbate the motion bar effect?
Slow motion can amplify the visibility of motion bars. Because slow-motion footage typically requires a faster shutter speed, the discrepancy between the shutter speed and light flicker becomes more pronounced.
FAQ 11: What are the best settings for filming under fluorescent lights?
Start with a shutter speed matching your region’s frequency (1/60th for 60Hz, 1/50th for 50Hz). Enable any anti-flicker settings on your camera. Experiment with slightly slower shutter speeds if needed. Consider supplementing or replacing the fluorescent lights with incandescent or LED lights designed for video.
FAQ 12: Can polarized filters help reduce motion bars?
No, polarized filters primarily reduce glare and reflections; they do not affect the frequency of light or the issue of flicker. They will not help in reducing or eliminating motion bars.
By understanding the relationship between shutter speed and the refresh rate of artificial lighting, and by utilizing the techniques outlined in this guide, you can significantly reduce or eliminate motion bars and create high-quality, flicker-free videos indoors. Remember to always test your settings before filming to ensure the best possible results.