Image obtained with high-speed camera shows how lightning rods work | Hacker News Reader

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

phys.org

92 pointswglb43 comments

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.

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.

Scary. At 6ft I wonder what kind of radiation dose you got.

I didn't think lightning produced any radiation, so I looked it up:

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"

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"

Fair, and yea, always evaluate sources critically but one (presumed) expert's assumption beats a pair of non-expert's speculation.

I did learn about "dark lightning" from that article which does produce gamma rays, which I found fascinating.

What's the right reaction in this situation? If you have nowhere to run, should you lie down?

I'm not sure, but we did not want to be the highest point, hence the run to shore.

Amusingly, John Wiseman's classic SAS survival handbook has advice for this situation.

  > You can sometimes sense that a lightning strike is imminent by a
  > tingling in the skin and the sensation of the hair standing on end. If
  > you are standing up, drop to the ground AT ONCE, going first to the
  > knees with the hands touching the ground. If you should be struck,
  > the charge may take the easiest route to the earth through your
  > arms - missing the torso and possibly saving you from heart failure
  > or asphixiation. QUICKLY LIE FLAT.

DO NOT LIE FLAT! You want to touch the ground in one point only, crouch/squat wit the feet close, if possible far from trees and on lower ground.

The article suggests that the best course of action in that case is to squat lo.

If you’re in an open powerboat, your best chance would be to apply full throttle and get the hell away from the storm as fast as you can, like the parent commenter did.

If you manage to find yourself in a lightning storm in a small, open sailboat, you’ve made a pretty big mistake, but essentially the same rule applies.

On larger vessels, if you’re belowdeck and aren’t touching anything metal, a lightning strike is usually a survivable incident, especially if your boat has a thoughtfully designed lightning protection system. All this involves is making sure you give the lightning a low-resistance path to ground through your boat’s keel and then the water that doesn’t run through anything expensive.

edit: I realize now maybe you didn’t mean specifically in the “on a boat” situation. Hopefully this comment is maybe interesting to fellow salty sea dogs. Yarr.

Assuming on land, not on a boat, as that's been covered elsewhere (just GTFO).

In a car: stay inside, doors closed, avoid touching the frame & such.

In an open field: crouch down with your feet together, don't put hands on the ground. Find lower ground if you can, e.g. a ditch. Don't lay down, keep your feet together.

Do not go under a tree. If you're around a lot of trees, best spot is as far from the base of any tree as the tree is tall.

And while we're here, if you ever hit a utility pole with your car hard enough to risk damage to the electrical wires, exit the car by hopping onto both feet together & letting go of the car before you land, and carefully hop away with both feet together. If you can't hop, do a very slow shuffle with feet together.

Some beautiful shots of highlining in Switzerland: https://www.youtube.com/watch?v=iZAmoZvZMqE

They put up this really long line - 537 m - and it seems like it was burned off by "lightning", but I think this happens by such static build-up and no proper lightning will be seen. The voltage difference between the mountainsides rises and is enough to cut the line, far earlier than any lightning strikes?

In the video they show the burned line at around the 6:20 mark.

Reminds me of this: https://www.youtube.com/watch?v=b9UO9tn4MpI

I've been what felt like pretty close to a lightning strike before, but I don't remember noticing anything like that. I was close enough that everything around me was illuminated like a camera flash, the sky behind the trees nearby looked bright white when it was a rainy, cloudy grey just moments before. The shadows on the ground looked stark and crisp and very long. The flash of light and the sound were simultaneous as far as I could tell. But the strangest thing for me, which I had never experienced before, was I could feel the ground shake as well. At first I thought it was some kind of explosion but as I ran as fast as I could I realized it must have been lightning.

The scariest part was later when I went to check again what the speed of sound was and I saw about 340 m/s, then I realized for the sound to be apparently simultaneous with the light, it would probably have had to have been no more than 250 ms behind the flash, conservatively, or I probably would have noticed the delay. Using that as an upper bound it puts the strike at no more than 85 meters away. Realistically it might have been in the neighborhood of 50ms, as I don't think I could perceive that difference at all. That would have put it about 17 meters away, but I wonder then if I would have been within range for electrocution had that been the case. The ground was soaked but I was walking on asphalt, if that makes any difference. Searching now I see lightning can arc horizontally on the ground around 20m, so maybe it was really somewhere between 50 and 250 meters away.

> The flash of light and the sound were simultaneous as far as I could tell. But the strangest thing for me, which I had never experienced before, was I could feel the ground shake as well.

When I was a kid, a lightning bolt hit a wood utility pole and exploded a hole about an adult's height deep & wide in the ground where the pole was mounted. I'll believe "ground shakes like buried TNT was blown up".

Some more slow motion videos from Dr. Saba:

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/

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.

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.

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.

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.

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.

Link to video:

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

Why does the video go all white in the middle?

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.

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.

The precursors and the big flash have very different brightness, that's what it looks like.

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-...

https://www.weather.gov/safety/lightning-science-connection-...

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://www.youtube.com/watch?v=JVXy-ZqqZ-g

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.

… 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.

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.

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?

They could use a second camera with smaller aperture and combine the images. HDR. But twice as expensive.

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.

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?

Yes? It’s a site that republishes press releases, they simply wouldn’t exist if not for advertising income.

With uBlock Origin blocking by default all the javascript, I read the artcile and never once saw a cookie consent pane.

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.

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.

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.'"

"Easy" implies attraction so I pretty strongly disagree with the way that is phrased.

People were complaining about the cookie consent, so I went to the video link.

Quality of website and rate of RTFM are correlated.

> 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?

Reply on news.ycombinator.com