Score
Title
14482
The Unabomber’s cabin, held in an FBI storage facility on an airforce base in Sacramento
29089
Brendan Fraser on His Comeback, Disappearance, and the Experience that Nearly Ended His Career
24538
me_irl
23856
Man removes feds’ spy cam, they demand it back, he refuses and sues
9672
In a Berlin metro. The text reads, "This text has no other purpose than to terrify those afraid of the Arabic language."
12173
This is the cleanest Saber ignition in all of Star Wars, she's a Badass
54438
"I hate everyone...except you."
6681
McDonald's plans to drop foam packaging globally by 2019 and will also switch to packaging made from recycled materials in every location by 2020.
5856
FrontEnd VS BackEnd
8604
You can do anything on your last day
13089
I'm not a good LEGO-ist but I'm proud of my lil' security camera.
10487
Or they’ll get shot first.
8611
Abandoned beach house in the Outer Banks, North Carolina, slowly being reclaimed by the sea. [1426 × 950]
18243
I don't think that's how that meme works...
6140
A sea turtle swimming up to take a nap in a giant barrel sponge
8517
Running a Solo business
59562
TIL Bhutan is the world's only carbon negative country. The constitution demands at least 60% of the country covered in forest, making it a sink of over four million tonnes of CO2 per year.
17175
PsBattle: Picasso holding a gun
13964
RaF pIlOt TrIeS tO tAkE oFf FrOm BeHiNd EnEmY lInEs
20609
The hero we need, but not the hero we deserve.
5250
I had to bribe the school photographer to let me do this my senior year.
17538
The sky before sunset at Tre Cime di Lavaredo in the dolomites, South Tyrol, Italy[1600 x 820] © By Carlos F. Turienzo
4804
"The why do I have diarrhea all the time" Starter pack
5921
They play just like humans. Pure joy.
18755
The mouse hole we put in the wall when we gutted our house. The light inside is motion activated and the wallpaper is vintage and from a flea market in England.
12446
Cat v.s. ewe
10538
Libraries are tossing millions of books to make way for study spaces and coffee shops
11344
A Wendy's employee using an outdoor table umbrella to walk an elderly customer to their car.
17272
Oh no! Pupper down call 91 bork
9724
When someone wont admit they're wrong but you can downvote them anyway.
8296
Spray paint spirograph
7174
[IMAGE] "Worry Is a Total Waste of Time"
31471
Woman finds her corgi comforting grieving stranger in the airport
7124
Clay turtle I made for my fiancé, who has been sending me the turtle emoji daily for the past 2+ years
3769
[Elon on Instagram] “Going to try to catch the giant fairing (nosecone) of Falcon 9 as it falls back from space at about eight times the speed of sound.”
56032
I got you bro, I got you
13345
This was unexpected
11153
Let's Dance.
4890
Seen in Warsaw, Poland!
13757
Do you ever just wake up and kiss the person sleeping beside you and feel glad that you are alive?
2383 Agouti They look like they are strobing because (for most of them) on mains power they actually are! Much like when whatching TV, however, something called ”persistence of vision” smooths it all out for you. When blinking or looking away quickly your brain "preserves" what you saw in that instant and you can spot it. You can also see it when something is moving quickly across your vision. Similar stuff happens when you dim LEDs (like LED car taillights when the brakes aren't on), though much, much faster through something called PWM. The LEDs are switched on and off really quickly - when they are on for half the time they look half as bright. In theory PWM is too fast to be perceivable (when done right) but it seems a lot of people are actually sensitive to it! You can also get strobing from HID headlights because they often use AC to get the thousands of volts they need to ignite. *This bit goes a little beyond ELI5 but hopefully still helps. My inbox kinda exploded and I've tried to answer repeated questions in the edits.* Strobing is (historically) very common with LEDs driven from mains AC. You can often see the effect if you wave your hand back and forth while focusing on a stationary spot - instead of smooth motion blur you can see a series of hand images, like stills from a movie. Cheap camera phones also sometimes show it. So why does this happen with LEDs but not other lights? In your mains AC, the voltage alternates from positive to negative and back again 50 or 60 times per second. That means that 100 or 120 times a second the voltage is exactly **zero.** Zero voltage, zero power. In traditional incandescent lights there is a fillament which is heated super hot to provide light. This fillament takes time to cool down - much longer than the mains supply takes to go through zero - and so it can stay hot, keep putting out light, and there is (almost) no flicker. In LEDs, there is no fillament to heat and they react *very* quickly. When the voltage to them starts to drop towards zero, the lights dim and turn off, coming back on again as it voltage goes back up. As this is happening at 100 or 120 Hz, most people wont notice it. Cheap or traditional triac based dimming can seriously exacerbate the issue with mains strobing. In higher quality power supplies for LEDs, they use "smoothing capacitors" and/or purpose designed LED drivers to help the LED stay lit through the low/zero volt bits and this reduces the strobing effect. Incidentally, flourescents also strobe (though to a lesser degree) and most video cameras have special software to help hide this. Obviously with battery (DC) powered stuff, excluding dimming, there is no AC and so no strobing. **E:** typos **Late E2+:** Some battery powered things can use DC to DC transformers which can in turn cause strobing, so the above has caveats. LED car headlights may fall into this category. I have assumed above that we are talking about incandescent replacement globes which almost always have a full bridge rectifier. For single diode lights (Christmas lights, dim indicators, or other decorative lighting) it is half the frequency and more noticeable. The flicker many people mention in slow motion footage of car LED taillights is almost certainly PWM dimming for combo brakes/running lights. Brakes on, full power, running lights, dimmed. **Regarding strobing headlights**, chances are they are HID lights not LED. HIDs need thousands of volts and have transformers (called ballasts) to get this, in turn meaning almost certainly an AC voltage being produced. Much like flourescent tubes, or arc lamps, there is no fillament to help it ride the zero crossing in the AC signal and they strobe. If it is absolutely LED then I would suspect it has to do with being a fancy matrix LED configuration which automatically controls the beam pattern (PWM?). Might also be DC to DC transformers at play. I also found it really interesting how many people have issues with PWM lights. Common wisdom used to be anything above 1 kHz was impossible to see with the naked eye... the exact frequency used in PWM is kinda arbitrary though, apart from lower is easier. Nothing stopping someone using PWM at say 200 Hz instead, which might be where the issue lies. If strobing bothers you the good news seems to be that a lot of newer high quality LED globes have switch-mode and/or smoothing built in, however it's not clear how to tell from the box. I did a search on Amazon and I couldn't find the right magic words. YMMV. If you have the chance to use them in person, at least one variety will stay on for a fraction of a second after you turn them off, so you might be able to look for this. Dimmable sorts might also be better.
1154 mmmmmmBacon12345 They're often dimmed using PWM(pulse-width modulation) in cheap applications. Basically they're turned on and off really quickly and by changing the ratio of on time to off time you can change how bright it appears to your eyes. The problem with this is that when they move through your vision(you turn your head or they move) or you wave something in front of them you'll get weird results because its not on all the time. There is a distinct image that only appears at specific locations on your retina instead of being a blurry smear across it like your brain expects from a continuous source. Good applications will instead provide constant power and control how much current is flowing through the LED. Providing constant power means they aren't turning on and off and don't leave you with the weird jittering effect.
11 ABrokenBinding The short answer is that it is a relationship between the frequency at which the driver operates and the visible flicker that the human eye can see from an LED light source. LEDs are DC components by nature. Apply a DC voltage and current, and voila! Light. Commercializing such a device requires extra components, specifically an LED driver, which takes the AC that your home provides and coverts it to DC that can then power a series of LEDs. These drivers have an operational frequency, the rate at which they cycle the power to the LED. In modern LED lamps, these frequencies are well north of 2000 Hz. However, a driver that is compact enough to fit in a retrofit lamp comes at a cost. So some manufacturers will still use drivers that operate at 100 Hz to save money/cut corners. That's all well and good, however research in the past 20-some years has shown that the human eye can detect LED flicker at an average of 100 - 120 Hz in LED sources. Why is this not a problem with the old tungsten lamps, you ask? Well, LEDs turn on and off instantly in response to the power supplied to them, on the order of microseconds, while tungsten lamps operate by heating a filament to a peak temperature. 50 or 60 Hz is not perceivable by the human eye when the rate of change is so slow, in this case hundredths of seconds. Filament heats up, cools down, rinse, repeat, but that change is slower than the power cycle of your house. In general, most modern LED lamps/retrofits don't have this issue anymore as the cost of components has dropped precipitously to the point where practically anyone can compete in the open market with LED products. Dimming, specifically PWM dimming of LED lamps using residential wave form chopping dimmers, is an entirely different matter. Mostly because cross-manufacturer standards are slow to solidify. Source: M.S. from the Lighting Research Center at Rensselaer Polytechnic Institute, and years of developing LED lighting fixtures for commercial applications.
2376 0 Agouti They look like they are strobing because (for most of them) on mains power they actually are! Much like when whatching TV, however, something called ”persistence of vision” smooths it all out for you. When blinking or looking away quickly your brain "preserves" what you saw in that instant and you can spot it. You can also see it when something is moving quickly across your vision. Similar stuff happens when you dim LEDs (like LED car taillights when the brakes aren't on), though much, much faster through something called PWM. The LEDs are switched on and off really quickly - when they are on for half the time they look half as bright. In theory PWM is too fast to be perceivable (when done right) but it seems a lot of people are actually sensitive to it! You can also get strobing from HID headlights because they often use AC to get the thousands of volts they need to ignite. *This bit goes a little beyond ELI5 but hopefully still helps. My inbox kinda exploded and I've tried to answer repeated questions in the edits.* Strobing is (historically) very common with LEDs driven from mains AC. You can often see the effect if you wave your hand back and forth while focusing on a stationary spot - instead of smooth motion blur you can see a series of hand images, like stills from a movie. Cheap camera phones also sometimes show it. So why does this happen with LEDs but not other lights? In your mains AC, the voltage alternates from positive to negative and back again 50 or 60 times per second. That means that 100 or 120 times a second the voltage is exactly **zero.** Zero voltage, zero power. In traditional incandescent lights there is a fillament which is heated super hot to provide light. This fillament takes time to cool down - much longer than the mains supply takes to go through zero - and so it can stay hot, keep putting out light, and there is (almost) no flicker. In LEDs, there is no fillament to heat and they react *very* quickly. When the voltage to them starts to drop towards zero, the lights dim and turn off, coming back on again as it voltage goes back up. As this is happening at 100 or 120 Hz, most people wont notice it. Cheap or traditional triac based dimming can seriously exacerbate the issue with mains strobing. In higher quality power supplies for LEDs, they use "smoothing capacitors" and/or purpose designed LED drivers to help the LED stay lit through the low/zero volt bits and this reduces the strobing effect. Incidentally, flourescents also strobe (though to a lesser degree) and most video cameras have special software to help hide this. Obviously with battery (DC) powered stuff, excluding dimming, there is no AC and so no strobing. **E:** typos **Late E2+:** Some battery powered things can use DC to DC transformers which can in turn cause strobing, so the above has caveats. LED car headlights may fall into this category. I have assumed above that we are talking about incandescent replacement globes which almost always have a full bridge rectifier. For single diode lights (Christmas lights, dim indicators, or other decorative lighting) it is half the frequency and more noticeable. The flicker many people mention in slow motion footage of car LED taillights is almost certainly PWM dimming for combo brakes/running lights. Brakes on, full power, running lights, dimmed. **Regarding strobing headlights**, chances are they are HID lights not LED. HIDs need thousands of volts and have transformers (called ballasts) to get this, in turn meaning almost certainly an AC voltage being produced. Much like flourescent tubes, or arc lamps, there is no fillament to help it ride the zero crossing in the AC signal and they strobe. If it is absolutely LED then I would suspect it has to do with being a fancy matrix LED configuration which automatically controls the beam pattern (PWM?). Might also be DC to DC transformers at play. I also found it really interesting how many people have issues with PWM lights. Common wisdom used to be anything above 1 kHz was impossible to see with the naked eye... the exact frequency used in PWM is kinda arbitrary though, apart from lower is easier. Nothing stopping someone using PWM at say 200 Hz instead, which might be where the issue lies. If strobing bothers you the good news seems to be that a lot of newer high quality LED globes have switch-mode and/or smoothing built in, however it's not clear how to tell from the box. I did a search on Amazon and I couldn't find the right magic words. YMMV. If you have the chance to use them in person, at least one variety will stay on for a fraction of a second after you turn them off, so you might be able to look for this. Dimmable sorts might also be better.
1160 0 mmmmmmBacon12345 They're often dimmed using PWM(pulse-width modulation) in cheap applications. Basically they're turned on and off really quickly and by changing the ratio of on time to off time you can change how bright it appears to your eyes. The problem with this is that when they move through your vision(you turn your head or they move) or you wave something in front of them you'll get weird results because its not on all the time. There is a distinct image that only appears at specific locations on your retina instead of being a blurry smear across it like your brain expects from a continuous source. Good applications will instead provide constant power and control how much current is flowing through the LED. Providing constant power means they aren't turning on and off and don't leave you with the weird jittering effect.
10 0 ABrokenBinding The short answer is that it is a relationship between the frequency at which the driver operates and the visible flicker that the human eye can see from an LED light source. LEDs are DC components by nature. Apply a DC voltage and current, and voila! Light. Commercializing such a device requires extra components, specifically an LED driver, which takes the AC that your home provides and coverts it to DC that can then power a series of LEDs. These drivers have an operational frequency, the rate at which they cycle the power to the LED. In modern LED lamps, these frequencies are well north of 2000 Hz. However, a driver that is compact enough to fit in a retrofit lamp comes at a cost. So some manufacturers will still use drivers that operate at 100 Hz to save money/cut corners. That's all well and good, however research in the past 20-some years has shown that the human eye can detect LED flicker at an average of 100 - 120 Hz in LED sources. Why is this not a problem with the old tungsten lamps, you ask? Well, LEDs turn on and off instantly in response to the power supplied to them, on the order of microseconds, while tungsten lamps operate by heating a filament to a peak temperature. 50 or 60 Hz is not perceivable by the human eye when the rate of change is so slow, in this case hundredths of seconds. Filament heats up, cools down, rinse, repeat, but that change is slower than the power cycle of your house. In general, most modern LED lamps/retrofits don't have this issue anymore as the cost of components has dropped precipitously to the point where practically anyone can compete in the open market with LED products. Dimming, specifically PWM dimming of LED lamps using residential wave form chopping dimmers, is an entirely different matter. Mostly because cross-manufacturer standards are slow to solidify. Source: M.S. from the Lighting Research Center at Rensselaer Polytechnic Institute, and years of developing LED lighting fixtures for commercial applications.