3 ms·

Link to video: https://youtube.com/watch?v=83UOoFWRCug https://youtube.com/watch?v=83UOoFWRCug

by O__________O 4y ago

mhb 4y ago
Why does the video go all white in the middle?
- jacquesm 4y ago
  Sensor white-out. The exposure length is long enough to catch the bulk of the strike and that changes the amount of light on the sensor to such a degree that all of the sensor pixels max out in terms of charge, so you get a white image.
  - mhb 4y ago
    OK. But what is happening in the video when that happens? Is the lightning striking right in front of the camera? I thought we were just watching the somewhat far away strikes evolve. Seems like the answer is obvious to everyone else though.
    - kzrdude 4y ago
      The precursors and the big flash have very different brightness, that's what it looks like.
    - mannykannot 4y ago
      The bright, branching, jagged lines reaching up and down are not the lightning bolts themselves, but stepped leaders (down) and streamers (up). They are ionized channels of air, and they grow at their tips because that is where the electric field strength is highest (it is analogous to crack propagation in solid materials, where the stress is concentrated at the tip.) At this point, there is still an insulating gap between them, and the only current in these channels is due to the rate at which this ionization progresses. Once the leaders connect the cloud to the ground, however, there is essentially a short-circuit between them, and a much greater current can flow - the return stroke. It is usually this you see when you see a lightning stroke, and it is far brighter than the leaders and streamers. The sensitivity (aperture?) of this camera is set to capture the leaders, and is overwhelmed by the brightness of the return stroke. In this case, there seem to have been two bolts in quick succession, with the second hitting a nearby building on the right. https://www.weather.gov/safety/lightning-science-initiation-leaders https://www.weather.gov/safety/lightning-science-initiation-... https://www.weather.gov/safety/lightning-science-connection-ground https://www.weather.gov/safety/lightning-science-connection-... https://www.weather.gov/safety/lightning-science-return-stroke https://www.weather.gov/safety/lightning-science-return-stro... In these videos, you can see the ionization occurring at the tips of the leaders (play the first at 0.25 speed): https://youtu.be/qQKhIK4pvYo?t=306 https://youtu.be/qQKhIK4pvYo?t=306 https://www.youtube.com/watch?v=JVXy-ZqqZ-g https://www.youtube.com/watch?v=JVXy-ZqqZ-g
- Anarch157a 4y ago
  My understanding is that the bolts you see approaching each other are precursors. When they touch, the circuit is completed and the current starts flowing, creating the bright flash we associate with lightning. That saturates the camera's sensor. The left-over bolts are just extremely hot air left in the path of the discharge.
- mock-possum 4y ago
  … I can’t tell if this is a serious comment It’s because the lightning strike is so bright that it completely blows out the camera’s sensor - there are so many photons that the photoreceptors are completely saturated.
  - detrites 4y ago
    Though I knew exactly what it was, I was also confused by it. The title implied that what was previously hidden was going to be revealed. Then, a large chunk of what happened continuing to be entirely obscured was disorienting. I thought there'd at least be more, eg a second camera where the part during the flash would be revealed, as I'd have expected if someone set up to film lightning in slo-mo they'd have set a sensible exposure for the purpose.
- anonu 4y ago
  Not clear why you're being downvoted as its a great question. I agree w/ the answers already provided - the digital sensors are probably over-saturated - which begs the question can it be fixed. My belief is that any sort of automatic exposure compensation, especially with a high frame-rate camera, on a dark night isn't going to be fast enough. Anyone have experience with high-speed cameras shooting in the dark?
  - mhb 4y ago
    They could use a second camera with smaller aperture and combine the images. HDR. But twice as expensive.

Link to video: https://youtube.com/watch?v=83UOoFWRCug https://youtube.com/watch?v=83UOoFWRCug

mhb 4y ago

Why does the video go all white in the middle?

jacquesm 4y ago
Sensor white-out. The exposure length is long enough to catch the bulk of the strike and that changes the amount of light on the sensor to such a degree that all of the sensor pixels max out in terms of charge, so you get a white image.
- mhb 4y ago
  OK. But what is happening in the video when that happens? Is the lightning striking right in front of the camera? I thought we were just watching the somewhat far away strikes evolve. Seems like the answer is obvious to everyone else though.
  - kzrdude 4y ago
    The precursors and the big flash have very different brightness, that's what it looks like.
  - mannykannot 4y ago
    The bright, branching, jagged lines reaching up and down are not the lightning bolts themselves, but stepped leaders (down) and streamers (up). They are ionized channels of air, and they grow at their tips because that is where the electric field strength is highest (it is analogous to crack propagation in solid materials, where the stress is concentrated at the tip.) At this point, there is still an insulating gap between them, and the only current in these channels is due to the rate at which this ionization progresses. Once the leaders connect the cloud to the ground, however, there is essentially a short-circuit between them, and a much greater current can flow - the return stroke. It is usually this you see when you see a lightning stroke, and it is far brighter than the leaders and streamers. The sensitivity (aperture?) of this camera is set to capture the leaders, and is overwhelmed by the brightness of the return stroke. In this case, there seem to have been two bolts in quick succession, with the second hitting a nearby building on the right. https://www.weather.gov/safety/lightning-science-initiation-leaders https://www.weather.gov/safety/lightning-science-initiation-... https://www.weather.gov/safety/lightning-science-connection-ground https://www.weather.gov/safety/lightning-science-connection-... https://www.weather.gov/safety/lightning-science-return-stroke https://www.weather.gov/safety/lightning-science-return-stro... In these videos, you can see the ionization occurring at the tips of the leaders (play the first at 0.25 speed): https://youtu.be/qQKhIK4pvYo?t=306 https://youtu.be/qQKhIK4pvYo?t=306 https://www.youtube.com/watch?v=JVXy-ZqqZ-g https://www.youtube.com/watch?v=JVXy-ZqqZ-g
Anarch157a 4y ago
My understanding is that the bolts you see approaching each other are precursors. When they touch, the circuit is completed and the current starts flowing, creating the bright flash we associate with lightning. That saturates the camera's sensor. The left-over bolts are just extremely hot air left in the path of the discharge.
mock-possum 4y ago
… I can’t tell if this is a serious comment It’s because the lightning strike is so bright that it completely blows out the camera’s sensor - there are so many photons that the photoreceptors are completely saturated.
- detrites 4y ago
  Though I knew exactly what it was, I was also confused by it. The title implied that what was previously hidden was going to be revealed. Then, a large chunk of what happened continuing to be entirely obscured was disorienting. I thought there'd at least be more, eg a second camera where the part during the flash would be revealed, as I'd have expected if someone set up to film lightning in slo-mo they'd have set a sensible exposure for the purpose.
anonu 4y ago
Not clear why you're being downvoted as its a great question. I agree w/ the answers already provided - the digital sensors are probably over-saturated - which begs the question can it be fixed. My belief is that any sort of automatic exposure compensation, especially with a high frame-rate camera, on a dark night isn't going to be fast enough. Anyone have experience with high-speed cameras shooting in the dark?
- mhb 4y ago
  They could use a second camera with smaller aperture and combine the images. HDR. But twice as expensive.