5 ms·

Image obtained with high-speed camera shows how lightning rods work

92 points by wglb 4y ago

anon111332142 4y ago
[flagged]
djaychela 4y ago
Not sure about the article content, but the cookie consent on this site needs work... Why is this so difficult? Do they really make so much from tracking data that it's worth annoying people?
- Luc 4y ago
  Yes? It’s a site that republishes press releases, they simply wouldn’t exist if not for advertising income.
- pwg 4y ago
  With uBlock Origin blocking by default all the javascript, I read the artcile and never once saw a cookie consent pane.
O__________O 4y ago
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.
hinkley 4y ago
When this was last explained to me, the lightning part of the lightning rod's job is only the visible part. By being sharp and pointy they work as an electrostatic emitter, reducing the potential energy between the ground and the clouds.
- mhb 4y ago
  TFA: "Lightning rods neither attract nor repel strikes, he added. Nor do they 'discharge" clouds, as used to be believed. They simply offer lightning an easy and safe route to the ground.'"
  - jacquesm 4y ago
    "Easy" implies attraction so I pretty strongly disagree with the way that is phrased.
  - hinkley 4y ago
    People were complaining about the cookie consent, so I went to the video link. Quality of website and rate of RTFM are correlated.
- kqr 4y ago
  > Lightning rods neither attract nor repel strikes, he added. Nor do they "discharge" clouds, as used to be believed. They simply offer lightning an easy and safe route to the ground. Is that not a refutation of the explanation you've had?
WalterBright 4y ago
I was once on a small boat with friends out on a lake. It was cloudy, but not threatening. Suddenly, we notice that so-and-so's hair was beginning to fluff up, and we laughed. Soon that happened to all of us. One of us realized what was happening, and we did an emergency full speed run to the shore. No lightning appeared, we were darn lucky.
- drewmol 4y ago
  Interesting. While in high school, a friend and I sailed his boat to the Lake Erie islands for the weekend. On our return trip a storm came up on us very quickly, we headed for the closest harbor but got caught in the thick of it anyways. I saw a lightning bolt hit the water 6 feet in front of me and split in two to hit two massive boulders in the river bed, the whole river illuminated for a second during the strike, coolest and scariest moment of my life.
  - sockaddr 4y ago
    Scary. At 6ft I wonder what kind of radiation dose you got.
    - jasonjayr 4y ago
      I didn't think lightning produced any radiation, so I looked it up: https://hps.org/publicinformation/ate/q10893.html https://hps.org/publicinformation/ate/q10893.html Looks like the answer is: "not enough to be worry some, and even less if it's not a direct hit"
      - sockaddr 4y ago
        Thanks for pulling that up, it was an interesting read. However they form their conclusion based on: > assuming that the lightning bolt produces as much radiation as an industrial x-ray machine Where was that pulled from? Then: > a person who is close to the bolt would receive about a tenth of a fatal dose That is actually quite a problem if we just take their assumptions for granted Then they even say: > As far as I know, however, there are no direct radiation dose measurements from this dark lightning so we don't really know exactly what the dose is So basically that expert's opinion amounts to "lets make an assumption based on literally nothing, based on that it's only 1/10th of what's needed to kill you but even then we have no data so this is all made up"
dcanelhas 4y ago
Back in early 2000s there were some supposed Early Streamer Emission (ESE) rods that claimed to reduce the need for rods by supposedly initiating the upward stream earlier, causing interception further away from the rod location. That tech has been quite thoroughly debunked (there was a big retrospective study in Malaysia that settled it, iirc). I remember seeing these systems being marketed by quite a lot of serious people at trade shows. Anyway, that's a bit off topic but i meant to say that it's cool to actually see the two streamers on a picture like that.
SiVal 4y ago
The article says lightning rods don't attract lightning. They just give it a safe path to ground. That makes no sense. Lightning pushes (& pulls) against resistance. Most current will follow the path of least resistance. A lightning rod is installed with two parts: 1) a "rod" that just by itself is designed to attract the strike to a sharpened electric field, and 2) a least-resistance path to ground in order to attract the current to follow that path instead of some other. That bolt in the photo extending upward is current being pulled up from the ground (or pushed down) with low resistance to attract the searching fingers of the bolt coming down from the cloud. The bolts reaching up to connect are going to be the most attractive to the bolt coming down. So how is it that "lightning rods don't attract lightning"? Maybe they just mean that they won't cause electrical storms.
- ot 4y ago
  I think it means that they do not cause lightning that would not have happened if the rod wasn't there. They just steer sparks that would have happened anyway.
- tlb 4y ago
  As I understand it, the distance over which the increased field gradient from a sharpened rod is greater than the variation in field gradient due to rain & wind is pretty small. Once the discharge has ionized the air to within several meters of the rod it'll probably find it, but it might not get close enough.
- yencabulator 4y ago
  People used to be afraid of installing them. That was essentially a marketing slogan saying you won't get more lightning because of the rod. I think this photo is great proof that the rods don't really make the lightning deviate from its path by much, it's more that instead of hitting the building it'll flow through the safe route to ground.
js2 4y ago
Some more slow motion videos from Dr. Saba: https://www.weather.gov/safety/lightning-science-slow-motion-flashes https://www.weather.gov/safety/lightning-science-slow-motion... The University of Florida has a lighting research lab with an ancient (and poorly maintained...) web site: http://www.lightning.ece.ufl.edu/ http://www.lightning.ece.ufl.edu/ I grew up in FL and currently live in NC, U.S. states #1 and #2 for lighting frequency. Summers here in NC involve frequently unplugging stuff around my house. Despite that, I've still lost about $5000 or so in gear over the years, everything from garage door openers (was able to repair those), to A/C furnace and compressor control boards to HDMI and Ethernet ports, cable modems, etc. HDMI and Ethernet ports seem particularly sensitive to ESD. About 5 years ago I installed type 2 SPDs on each of my panels. I also switched my ISP from coaxial cable to fiber optic. Haven't lost any equipment since, but maybe I've just been lucky recently.
tlb 4y ago
High-speed cameras are fascinating to observe things with. I use them a lot for robotics, but almost any physical phenomenon has a great deal of detail only visible at higher speeds than the eye is capable of. Your phone camera can probably do 240 fps, which is great, but you can see even more at 1k or 10k fps.

92 points by wglb 4y ago

[flagged]

Not sure about the article content, but the cookie consent on this site needs work... Why is this so difficult? Do they really make so much from tracking data that it's worth annoying people?

Luc 4y ago
Yes? It’s a site that republishes press releases, they simply wouldn’t exist if not for advertising income.
pwg 4y ago
With uBlock Origin blocking by default all the javascript, I read the artcile and never once saw a cookie consent pane.

O__________O 4y ago

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.

hinkley 4y ago

When this was last explained to me, the lightning part of the lightning rod's job is only the visible part. By being sharp and pointy they work as an electrostatic emitter, reducing the potential energy between the ground and the clouds.

mhb 4y ago
TFA: "Lightning rods neither attract nor repel strikes, he added. Nor do they 'discharge" clouds, as used to be believed. They simply offer lightning an easy and safe route to the ground.'"
- jacquesm 4y ago
  "Easy" implies attraction so I pretty strongly disagree with the way that is phrased.
- hinkley 4y ago
  People were complaining about the cookie consent, so I went to the video link. Quality of website and rate of RTFM are correlated.
kqr 4y ago
> Lightning rods neither attract nor repel strikes, he added. Nor do they "discharge" clouds, as used to be believed. They simply offer lightning an easy and safe route to the ground. Is that not a refutation of the explanation you've had?

WalterBright 4y ago

I was once on a small boat with friends out on a lake. It was cloudy, but not threatening. Suddenly, we notice that so-and-so's hair was beginning to fluff up, and we laughed. Soon that happened to all of us. One of us realized what was happening, and we did an emergency full speed run to the shore. No lightning appeared, we were darn lucky.

drewmol 4y ago
Interesting. While in high school, a friend and I sailed his boat to the Lake Erie islands for the weekend. On our return trip a storm came up on us very quickly, we headed for the closest harbor but got caught in the thick of it anyways. I saw a lightning bolt hit the water 6 feet in front of me and split in two to hit two massive boulders in the river bed, the whole river illuminated for a second during the strike, coolest and scariest moment of my life.
- sockaddr 4y ago
  Scary. At 6ft I wonder what kind of radiation dose you got.
  - jasonjayr 4y ago
    I didn't think lightning produced any radiation, so I looked it up: https://hps.org/publicinformation/ate/q10893.html https://hps.org/publicinformation/ate/q10893.html Looks like the answer is: "not enough to be worry some, and even less if it's not a direct hit"
    - sockaddr 4y ago
      Thanks for pulling that up, it was an interesting read. However they form their conclusion based on: > assuming that the lightning bolt produces as much radiation as an industrial x-ray machine Where was that pulled from? Then: > a person who is close to the bolt would receive about a tenth of a fatal dose That is actually quite a problem if we just take their assumptions for granted Then they even say: > As far as I know, however, there are no direct radiation dose measurements from this dark lightning so we don't really know exactly what the dose is So basically that expert's opinion amounts to "lets make an assumption based on literally nothing, based on that it's only 1/10th of what's needed to kill you but even then we have no data so this is all made up"

dcanelhas 4y ago

Back in early 2000s there were some supposed Early Streamer Emission (ESE) rods that claimed to reduce the need for rods by supposedly initiating the upward stream earlier, causing interception further away from the rod location. That tech has been quite thoroughly debunked (there was a big retrospective study in Malaysia that settled it, iirc). I remember seeing these systems being marketed by quite a lot of serious people at trade shows. Anyway, that's a bit off topic but i meant to say that it's cool to actually see the two streamers on a picture like that.

SiVal 4y ago

The article says lightning rods don't attract lightning. They just give it a safe path to ground. That makes no sense. Lightning pushes (& pulls) against resistance. Most current will follow the path of least resistance. A lightning rod is installed with two parts: 1) a "rod" that just by itself is designed to attract the strike to a sharpened electric field, and 2) a least-resistance path to ground in order to attract the current to follow that path instead of some other. That bolt in the photo extending upward is current being pulled up from the ground (or pushed down) with low resistance to attract the searching fingers of the bolt coming down from the cloud. The bolts reaching up to connect are going to be the most attractive to the bolt coming down. So how is it that "lightning rods don't attract lightning"? Maybe they just mean that they won't cause electrical storms.

ot 4y ago
I think it means that they do not cause lightning that would not have happened if the rod wasn't there. They just steer sparks that would have happened anyway.
tlb 4y ago
As I understand it, the distance over which the increased field gradient from a sharpened rod is greater than the variation in field gradient due to rain & wind is pretty small. Once the discharge has ionized the air to within several meters of the rod it'll probably find it, but it might not get close enough.
yencabulator 4y ago
People used to be afraid of installing them. That was essentially a marketing slogan saying you won't get more lightning because of the rod. I think this photo is great proof that the rods don't really make the lightning deviate from its path by much, it's more that instead of hitting the building it'll flow through the safe route to ground.

js2 4y ago

Some more slow motion videos from Dr. Saba: https://www.weather.gov/safety/lightning-science-slow-motion-flashes https://www.weather.gov/safety/lightning-science-slow-motion... The University of Florida has a lighting research lab with an ancient (and poorly maintained...) web site: http://www.lightning.ece.ufl.edu/ http://www.lightning.ece.ufl.edu/ I grew up in FL and currently live in NC, U.S. states #1 and #2 for lighting frequency. Summers here in NC involve frequently unplugging stuff around my house. Despite that, I've still lost about $5000 or so in gear over the years, everything from garage door openers (was able to repair those), to A/C furnace and compressor control boards to HDMI and Ethernet ports, cable modems, etc. HDMI and Ethernet ports seem particularly sensitive to ESD. About 5 years ago I installed type 2 SPDs on each of my panels. I also switched my ISP from coaxial cable to fiber optic. Haven't lost any equipment since, but maybe I've just been lucky recently.

tlb 4y ago

High-speed cameras are fascinating to observe things with. I use them a lot for robotics, but almost any physical phenomenon has a great deal of detail only visible at higher speeds than the eye is capable of. Your phone camera can probably do 240 fps, which is great, but you can see even more at 1k or 10k fps.