rods

Silent Lightning

Silent Lightning

Lightning is silent, I think, because we say that it’s the thunder we hear (up to 12 or so miles away). But the two go hand in hand obviously. Lightning is becoming more silent due to the digital age. What that means is that our digital tv‘s don’t crackle with static and our radios are becoming more and more digital so it’s hard to tune in static or hear it anymore. Why is that? Our new technology is designed to interpret 1’s and 0’s so the various frequencies of sounds that would make the static in our old tv’s and radios…..is not detected in our new gadgets. Maybe lightning needs a digital upgrade.

Lightning occurs somewhere on this earth about 8 billion times a day. More lightning occurs when the weather is warmer so when it’s winter in the northern hemisphere our neighbors to the south get their share and the ones in the middle, they don’t get much of a break. We know where lightning is occurring practically instantaneously because we have satellites that detect subtle changes in the atmosphere. ¬†Even during the daytime these satellites apparently are good at detecting lightning 90% of the time including cloud to cloud and intracloud lightning.

I was reading a story about Ben Franklin and his debate with Royal Society members on whether his lightning rods were designed properly and if they did reduce the chance of lightning by defusing the atmosphere. It turns out that we can’t defuse the atmosphere and that long lightning rods are not necessarily better than short one foot ones. Gathering data about lightning strikes back then meant asking “respected” people what they might have witnessed. Even though the lightning rods we have now are very effective, interestingly, most typical houses don’t have lightning rods. They are found on more valuable structures. And many times these rods are hard to find because they can be blended into the structure.

What I really wanted to know about lightning though is how likely is a person in a swimming pool to be hurt by lightning. This would be a dangerous experiment because we’ve probably all read about someone being injured or dying from a lightning strike and we know that water conducts electricity. What I read from two different places on the internet is that a 20 foot distance would be needed and the other source said 200 feet. Since it’s easy to get out of the pool, that’s the best solution and getting out of indoor pools as well because plumbing could carry the electrical discharge into a pool. But apparently pools are unlikely to be hit by lightning since lightning likes taller structures. Still, easier to get out of pool than to depend on lightning hitting the lifeguard stand.

Most of us probably know about the method to calculate how far lightning is from us. Since sounds travels slower than light, it takes 4 – ¬†5 seconds for thunder to travel a mile after you see the flash (flash to bang). The lifeguard association recommends swimmers exit the pool when lightning is 10 miles away. That’s maybe 40 seconds at the quickest to get out of the pool. I don’t recall being that cautious when I was a lifeguard. Better safe than sorry though, right? If you disagree with the lifeguard, find another pool to take your chances.

Here are a couple of interesting things about lightning. It’s thickness is less than a half dollar coin but the length can be 3 miles long and there’s an interesting type of lightning called red sprite lightning which can occur above the clouds. See the link below for some cool pictures of that.

www.universetoday.com/96984/on-the-hunt-for-high-speed-sprites/

red sprite lightning

red sprite lightning

 

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Dark Adaptation Red Alert

Dark Adaptation Red Alert

I’ve wondered about the use of red for brake lights and tail lights. It’s a standardized system coded many years ago for countries to follow. But I sometimes have a hard time at night gauging where that car in front of me really is so I don’t have to slam on my brakes. Throw in some head lights and glare from oncoming cars and it’s not a pretty thing trying to stay out of trouble.

Most of you know about the rods and cones in our eyes, the light detecting photoreceptors in our retinas that is. During daylight hours when inside with normal lighting or outside during the daytime, our vision is sharp (for most of us) owing to how those cones work. They’re good for that kind of lighting. In very dark places we have the other photoreceptors, the rods, to help detect dim light but not colors. The rods don’t help at all with sharpness but they do tell us if there is a light on somewhere and those cells connect to each other unlike cones so they can add to each other’s light sensing effect. All those photoreceptors are working practically all the time but there is a light level where the rods and cones might shift to whichever is more effective for that lighting. See below for that graph.

But red light is a special thing. We detect light between 400nm and 760nm. This is the rainbow of colors where 400nm (nanometers) is violet. At the other end of the visible range of light we can detect, 760nm is red which has the least amount of energy of all the others. But violet isn’t just 400nm. It could look violet-ish at 430nm. And the same goes for red, give or take. And before all hell breaks loose here, I’ve read the visible spectrum may start a little lower than 400nm and the upper end might be a little higher than 760nm. Websites are all over the place with numbers and that’s like a lot of things by the way. Some things in life aren’t always clear or exact.

Here’s the great thing about red. If you turn off all lights and just use red light, you can see with it…of course…(even though the other cones are basically switched off). Maybe you won’t see as easily than with regular lighting but we can read (not red letters though). And why does any of that matter? If you want to be dark adapted, meaning, if you want to see in the dark but still need to read something written, you can do it with red light and it won’t negatively affect your ability to have good vision in the dark (by good I mean as good as we can possibly see in the dark). This is why red (I think) was chosen as the light color for brake and tail lights for at least night driving. This is also why you will find red lights in dark places like movie theaters or those exit signs we have everywhere. Red light won’t ruin your adapting to dark or dimly lit places.

And this is also interesting about red…..there is a point when lights get so dim that you can’t differentiate colors but if something has a red color you can still see it (not it’s red color but you can tell it’s there). When light is eventually dimmed completely, then there is no light at all for your eyes to detect (total darkness) so red is the last color standing! And…red alert means it’s getting pretty serious :), as in war time serious. Hiding in the dark still required seeing so red lights helped and pilots kept their dark adaptation by using red light or red goggles.

One more thing about red light. That long wavelength (almost twice as long as violet) actually focuses a bit “behind” our retina so those needing reading glasses or getting close to needing them…might have to bump up the reading power a bit if you’re going to read best in red light.

http://www.aoa.org/optometrists/tools-and-resources/clinical-care-publications/aviation-vision/the-eye-and-night-vision

This is a particular interesting “web book” on vision….http://www.yorku.ca/eye/thejoy.htm

light dark graph

light dark graph

 

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