The scientific reason you don’t like LED bulbs

http://theconversation.com/the-scientific-reason-you-dont-like-led-bulbs-and-the-simple-way-to-fix-them-81639

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. During the eye movement, the flicker of light creates a pattern that we can see. It could discourage people from using more energy-saving LED lightbulbs.

One obvious way of avoiding the flicker is to operate the lamps with a direct current so the light is constant, but this involves more expensive, shorter-lived components. 

When the light flickered 1,000 times a second the pattern could clearly be seen. At about 3,000 per second, the images became invisible.

In contrast, some LEDs flash only 400 times per second. 

Flashing happens especially when LEDs are dimmed with PWM.

2 Comments

  1. Tomi Engdahl says:

    History of White LEDs
    https://hackaday.com/2018/10/29/history-of-white-leds/

    Compared to incandescent lightbulbs, LEDs produce a lot more lumens per watt of input power — they’re more efficient at producing light. Of course, that means that incandescent light bulbs are more efficient at producing heat, and as the days get shorter, and the nights get colder, somewhere, someone who took the leap to LED lighting has a furnace that’s working overtime. And that someone might also wonder how we got here: a world lit by esoteric inorganic semiconductors illuminating phosphors.

    The fact that diodes emit light under certain conditions has been known for over 100 years; the first light-emitting diode was discovered at Marconi Labs in 1907 in a cat’s whisker detector, the first kind of diode.

    The first visible-spectrum LED was built at General Electric in 1962, with the first commercially available (red) LEDs produced by the Monsanto Company in 1968. HP began production of LEDs that year, using the same gallium arsenide phosphate used by Monsanto. These HP LEDs found their way into very tiny seven-segment LED displays used in HP calculators of the 1970s.

    From the infrared LEDs of the early 1960s to the red LEDs of the late 1960s, the 1970s saw orange-red, orange, yellow, and finally green LEDs.

    Infrared, red, and even green LEDs were “easy”, but blue LEDs require a much larger bandgap, and therefore required more exotic materials. The puzzle behind making a high-brightness blue LED was first cracked in 1994 at the Nichia Corporation using indium gallium nitride. At the same time, Isamu Akasaki and Hiroshi Amano at Nagoya University developed a gallium nitride substrate for LEDs, for which they won the 2014 Nobel Prize in Physics. With red, green, and blue LEDs, the only thing stopping anyone from building a white LED was putting all these colors in the same package.

    The first white LEDs weren’t explicitly white LEDs. Instead, red, green, and blue LEDs were packed into a single LED enclosure.

    This remains the standard for RGB LEDs, and some have even experimented with improving the range of color these LEDs can produce. The human eye is extremely sensitive to green frequencies of light, and by adding a fourth LED to a package — it’s best called ’emerald’, or a slightly bluer shade of green than what we’re used to in green LEDs — you can make an LED with a wider color range, or if you prefer, a whiter white.

    Those neopixels, WS2812s, or APA101s, all have red, green, and blue LEDs tucked inside one enclosure.

    The first white LEDs, made without three individual LEDs, were made with the magic of phosphors.

    With an ultraviolet or violet LED packaged inside a phosphor-coated enclosure, you can make a white LED. This is known as a full-conversion white LED.

    Full conversion LEDs are inefficient, though, so by the mid-90s the race was on to create a partial conversion LED. This type of LED would illuminate a phosphor with blue light, and the phosphor would convert a portion of that blue light into something broadly yellowish that contains a mixture of red and green wavelengths. Adding more red phosphors to the mix creates “warm white” LEDs.

    In 1996, the Nichia Company announced the production of white LEDs

    Reply
  2. Tomi Engdahl says:

    Better Living with a New Generation of Smart Lights
    https://www.electronicdesign.com/industrial-automation/better-living-new-generation-smart-lights?NL=ED-003&Issue=ED-003_20190116_ED-003_146&sfvc4enews=42&cl=article_1_b&utm_rid=CPG05000002750211&utm_campaign=22707&utm_medium=email&elq2=46c514e4eec74fb68c916afc1c0fa587

    Getting into a circadian rhythm: This article explains the science behind the new smart-lighting trend, and the technology that makes it possible.

    Reply

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