Answers.Body: <p>The reason is very simple. LED's are not constantly turned on, but flicker at a very high rate, usually due to fluctuations in your powerline. Your video camera records at a fixed framerate and as such, you can see these black lines.</p>
  
  <p>One way to counteract this is by not using an LED light source. But you may be able to work around this by setting a slower shutter speed (thanks to ths in the comments for this suggestion). You will likely need a tripod then though.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-15T13:29:44.133Z
Answers.Text: or by using a slower shutter speed.
Answers.UserDisplayName: ths
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Answers.Text: Battery-powered LED lamps will work, as will high-quality mains-powered LED bulbs, and (most) transformer-powered LED light strips.
Answers.UserDisplayName: Mark
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Answers.CreationDate: 2018-05-15T12:17:10.413Z
Answers.LastActivityDate: 2018-05-15T18:36:35.537Z
Answers.UserDisplayName: LPChip
Answers.Body: <p>LEDs are a very fast reacting light source, far faster reacting than incandescents or even flouresecents. So if the current through the LED varies rapidly the light output will vary equally rapidly. </p>
  
  <p>Cameras often have a "rolling shutter". Different parts of the frame are captured at different times. So time variation in the lighting becomes spacial variation in the image.</p>
  
  <p>There are several different possible causes of rapid variation in LED drive current and hence light output.</p>
  
  <ol>
  <li>Some very cheap LED lights just rectify the mains and feed is straight to the LEDs. </li>
  <li>Some LED drivers use the LEDs themselves as the diodes in a switched-mode converter.</li>
  <li>Some LED lights use pulse width modulation to adjust the brightness. Due to implementation even with the brightness control set to it's maximum value the on-time may not be quite 100%.</li>
  </ol>
  
  <p>Personally of the three possible causes I think you are dealing with number 3. The reason I think this is that the lines are very hard edged. With mains-derived flicker I would expect to see a gradual ramp up and down. With switchmode converter derived flicker I would expect to see a sharp transition from black to full brightness followed by a gradual fade out.</p>
  
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Answers.CreationDate: 2018-05-15T17:52:52.507Z
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Answers.UserDisplayName: Peter Green
Answers.Body: <blockquote>
  <p>Everytime I point a digital camera of some sort (webcam, phone, camcorder...) at my LED desk lamp or its light reflected off an object (only if the object is very reflective and/or near the lamp), I see some scrolling black lines that shift thickness and scrolling speed as I change white balance.</p>
  <p>What is the cause of this?</p>
  </blockquote>
  <p><a href="https://en.wikipedia.org/wiki/Pulse-width_modulation" rel="nofollow noreferrer"><strong>Pulse width modulation.</strong></a> A common way to vary the brightness of LED lights is to turn them on and off rapidly. The <em>duty cycle</em>, or the percentage of time when the light is on, determines the brightness. I assume that when you say you're changing the &quot;white balance,&quot; you mean that you're actually adjusting the lamp and not the camera. Decreasing the brightness of the lamp will result in wider black bars because the lamp spends more time off.</p>
  <blockquote>
  <p>Finally, my bedside lamp - also LED - creates no such phenomenon.</p>
  </blockquote>
  <p>The difference may simply be that your bedside lamp isn't dimmable, and so always runs at full brightness and, effectively, 100% duty cycle.</p>
  <p>Another difference may be in the way your bedside lamp is powered compared to your desk and ceiling lights. High-power LEDs are typically powered with a constant current driver, which prevents too much current from flowing through the LED modules and causing them to overheat. Lower-power LEDs, like those found in strip lights or lamps that use dozens of small LEDs instead of a few large ones, can be powered with constant voltage drivers instead. In this case, a current-limiting resistor or just the combined internal resistance of a number of LEDs powered in series can limit the amount of current that flows and keep the LEDs from overheating. So, your bedside lamp might use a constant voltage driver (or even just a battery) that doesn't work by turning the light off part of the time.</p>
  
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Answers.CreationDate: 2018-05-15T17:27:22.930Z
Answers.LastActivityDate: 2018-05-15T17:27:22.930Z
Answers.LastEditDate: 2020-06-17T09:53:03.607Z
Answers.UserDisplayName: Caleb
Answers.Body: <p>Cheap (to make) LED lights will flicker at twice the mains frequency. There are many ways of overcoming this in the design of lights, such as using a larger smoothing capacitor (which makes the light bulky), using a dedicated progressive LED driver IC (which turns off some of the LEDs but not all of them, so the light dims rather than going out every half cycle) or using a switched mode converter at a higher frequency (which is more complex than the more common capacitive dropper, but allows dimming - adjustable LED panels sold for use in photography will have this technology). </p>
  
  <p>Put a different bulb in the lamp, such as the one that's in your bedside lamp. Generally the more expensive and branded ones will have better smoothing circuitry.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-16T11:26:48.707Z
Answers.Text: @pipe - I upvoted the post, but not because of it mentioning only cheap led lights flicker- because it just isn't true. Some expensive ones flicker...
Answers.UserDisplayName: Dr Mayhem
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Answers.CreationDate: 2018-05-22T14:54:59.943Z
Answers.Text: @alex2003super you was robbed
Answers.UserDisplayName: Pete Kirkham
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Answers.LastActivityDate: 2018-05-22T14:54:25.220Z
Answers.LastEditDate: 2018-05-22T14:54:25.220Z
Answers.UserDisplayName: Pete Kirkham
Body: <p>Everytime I point a digital camera of some sort (webcam, phone, camcorder...) at my LED desk lamp or its light reflected off an object (only if the object is very reflective and/or near the lamp), I see some scrolling black lines that shift thickness and scrolling speed as I change white balance.</p>
  
  <p>They make it impossible for me to film uboxing and other videos using my desk lamp as light source. What is the cause of this? I also noticed my ceiling-mounted LED light produces a similar pattern as well albeit with thicker lines. Finally, my bedside lamp - also LED - creates no such phenomenon.</p>
  
  <p><strong>A photo of the LED light on my desk</strong></p>
  
  <p><a href="https://i.sstatic.net/IlfBr.jpg" rel="noreferrer"><img src="https://i.sstatic.net/IlfBr.jpg" alt="enter image description here"></a></p>
  
Tags: <camera>
Title: Digital cameras see black scrolling lines when filming light from my desk lamp
UserDisplayName: Manchineel
ThreadText: # Digital cameras see black scrolling lines when filming light from my desk lamp
  
  (Asked by: username_0 on 2018-05-15)
  
  Everytime I point a digital camera of some sort (webcam, phone, camcorder...) at my LED desk lamp or its light reflected off an object (only if the object is very reflective and/or near the lamp), I see some scrolling black lines that shift thickness and scrolling speed as I change white balance.
  
  They make it impossible for me to film uboxing and other videos using my desk lamp as light source. What is the cause of this? I also noticed my ceiling-mounted LED light produces a similar pattern as well albeit with thicker lines. Finally, my bedside lamp - also LED - creates no such phenomenon.
  
  **A photo of the LED light on my desk**
  
  [![enter image description here](https://i.sstatic.net/IlfBr.jpg)](https://i.sstatic.net/IlfBr.jpg)
  
  **Tags:** camera
  
  
  ---
  
  ## 4 answers
  
  ### Answer by username_6 on 2018-05-15. Score: 11 | Accepted answer
  
  Cheap (to make) LED lights will flicker at twice the mains frequency. There are many ways of overcoming this in the design of lights, such as using a larger smoothing capacitor (which makes the light bulky), using a dedicated progressive LED driver IC (which turns off some of the LEDs but not all of them, so the light dims rather than going out every half cycle) or using a switched mode converter at a higher frequency (which is more complex than the more common capacitive dropper, but allows dimming - adjustable LED panels sold for use in photography will have this technology).
  
  Put a different bulb in the lamp, such as the one that's in your bedside lamp. Generally the more expensive and branded ones will have better smoothing circuitry.
  
  > **Comments:**
  > **username_7**: @pipe - I upvoted the post, but not because of it mentioning only cheap led lights flicker- because it just isn't true. Some expensive ones flicker...  
  > **username_6**: @alex2003super you was robbed  
  
  ---
  
  ### Answer by username_1 on 2018-05-15. Score: 9
  
  The reason is very simple. LED's are not constantly turned on, but flicker at a very high rate, usually due to fluctuations in your powerline. Your video camera records at a fixed framerate and as such, you can see these black lines.
  
  One way to counteract this is by not using an LED light source. But you may be able to work around this by setting a slower shutter speed (thanks to ths in the comments for this suggestion). You will likely need a tripod then though.
  
  > **Comments:**
  > **username_2**: or by using a slower shutter speed.  
  > **username_3**: Battery-powered LED lamps will work, as will high-quality mains-powered LED bulbs, and (most) transformer-powered LED light strips.  
  
  ---
  
  ### Answer by username_4 on 2018-05-15. Score: 4
  
  LEDs are a very fast reacting light source, far faster reacting than incandescents or even flouresecents. So if the current through the LED varies rapidly the light output will vary equally rapidly.
  
  Cameras often have a "rolling shutter". Different parts of the frame are captured at different times. So time variation in the lighting becomes spacial variation in the image.
  
  There are several different possible causes of rapid variation in LED drive current and hence light output.
  
  1. Some very cheap LED lights just rectify the mains and feed is straight to the LEDs.
  2. Some LED drivers use the LEDs themselves as the diodes in a switched-mode converter.
  3. Some LED lights use pulse width modulation to adjust the brightness. Due to implementation even with the brightness control set to it's maximum value the on-time may not be quite 100%.
  
  Personally of the three possible causes I think you are dealing with number 3. The reason I think this is that the lines are very hard edged. With mains-derived flicker I would expect to see a gradual ramp up and down. With switchmode converter derived flicker I would expect to see a sharp transition from black to full brightness followed by a gradual fade out.
  
  
  ---
  
  ### Answer by username_5 on 2018-05-15. Score: 0
  
  > Everytime I point a digital camera of some sort (webcam, phone, camcorder...) at my LED desk lamp or its light reflected off an object (only if the object is very reflective and/or near the lamp), I see some scrolling black lines that shift thickness and scrolling speed as I change white balance.
  >
  > What is the cause of this?
  
  [**Pulse width modulation.**](https://en.wikipedia.org/wiki/Pulse-width_modulation) A common way to vary the brightness of LED lights is to turn them on and off rapidly. The *duty cycle*, or the percentage of time when the light is on, determines the brightness. I assume that when you say you're changing the "white balance," you mean that you're actually adjusting the lamp and not the camera. Decreasing the brightness of the lamp will result in wider black bars because the lamp spends more time off.
  
  > Finally, my bedside lamp - also LED - creates no such phenomenon.
  
  The difference may simply be that your bedside lamp isn't dimmable, and so always runs at full brightness and, effectively, 100% duty cycle.
  
  Another difference may be in the way your bedside lamp is powered compared to your desk and ceiling lights. High-power LEDs are typically powered with a constant current driver, which prevents too much current from flowing through the LED modules and causing them to overheat. Lower-power LEDs, like those found in strip lights or lamps that use dozens of small LEDs instead of a few large ones, can be powered with constant voltage drivers instead. In this case, a current-limiting resistor or just the combined internal resistance of a number of LEDs powered in series can limit the amount of current that flows and keep the LEDs from overheating. So, your bedside lamp might use a constant voltage driver (or even just a battery) that doesn't work by turning the light off part of the time.
  
  
  ---
  
  