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posted by martyb on Saturday July 29 2017, @06:53AM   Printer-friendly
from the need-a-faster-flicker dept.

Interesting article at Business Insider on why we don't like LED bulbs:

There's a handy trick for reading station signs that otherwise fly past in a blur as you travel in a high-speed train. Look at one side of the window and then immediately at the other side of the window. When you change your gaze, your eyes will automatically make a rapid jerking movement, known as a saccade. If the direction of the saccade is the same as that of the train, your eyes will freeze the image for a split second, long enough to read the station name if you time things right.

Saccades are very fast movements of the eyes. Their exact speed depends on the size of the movement, but large saccades can move the eyes at the same rate as a high-speed train. The image of the station name becomes visible because it is travelling at the same speed as the eye, and the images before and after the saccade are blurred and so don't interfere with the image of the sign. This shows us that our vision is still working when our eyes move rapidly during saccades.

Scientists used to think we could see no more than about 90 flashes of light a second but now we know it's more like 2,000 because the eyes move so rapidly when we change gaze from one point to another. During the eye movement, the flicker of light creates a pattern that we can see. And this has some surprising consequences for our health thanks to the way some types of lighting can affect us. In particular, it could discourage people from using more energy-saving LED lightbulbs.

Most lighting is electric and powered by an alternating current supply, which makes the bulbs continually dim and then brighten again at a very fast rate. Unlike filament lamps and to a lesser extent fluorescent lamps, LEDs don't just dim but effectively turn on and off completely (unless the current is maintained in some way).

The answer is not to make them less piercing?


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  • (Score: 1) by toddestan on Saturday July 29 2017, @11:52PM (1 child)

    by toddestan (4982) on Saturday July 29 2017, @11:52PM (#546483)

    It depends on the LED light. Any decent bulb made for household use is perfectly fine. The problems are LED christmas lights and similar decorative lights like those cheap rope lights which are run straight off the AC so they flicker at 60 Hz, which is very noticeable and annoying. Some LED taillights in cars use the "cycle the LEDs on/off very fast to make them look dim" technique, except they seem to use something around 50 Hz (so not actually that fast) which is also very noticeable and annoying when driving at night behind one of them. Seen most commonly on Cadillacs from a few years back but I've seen it on other cars and trucks.

    There's also the in-between solution used by some cheap but not totally cheap AC-driven LEDs that appear to use a full wave rectifier so they flicker at 120 Hz. Normally this is too fast to be perceive - I have some "flicker-free" LED christmas lights that use this technique (and many that claim to be flicker-free that clearly flicker at 60 Hz so buyer-beware). I don't see the 120 Hz flicker for my use, but I've seen some advertising signs that also do this and if you are moving fast like driving on the freeway then you can notice that they do flicker.

    If you really want to mess with those people though, be sure to remind them that their smartphones and tablets use LEDs to light up the screen, as well as most any relatively recent computer, laptop, and television.

  • (Score: 2) by JeanCroix on Monday July 31 2017, @01:09PM

    by JeanCroix (573) on Monday July 31 2017, @01:09PM (#547123)

    Some LED taillights in cars use the "cycle the LEDs on/off very fast to make them look dim" technique, except they seem to use something around 50 Hz (so not actually that fast) which is also very noticeable and annoying when driving at night behind one of them. Seen most commonly on Cadillacs from a few years back but I've seen it on other cars and trucks.

    As soon as I saw this article, Cadillac taillights immediately came to mind. Personally, those are the only LEDs I've ever found to seriously annoy my eyes. If I'm driving at night, I'll even switch lanes to avoid having those horrible flickery Caddy taillights anywhere in my field of vision.