The scientific reason you don’t like LED bulbs

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.


  1. Tomi Engdahl says:

    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

  2. Tomi Engdahl says:

    Better Living with a New Generation of Smart Lights

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

  3. Tomi Engdahl says:

    Selectronic – Sunlight spectrum LEDs are close to actual sunlight

    Selectronic and their Chinese partners HongliTronic can provide artificial lighting in a home or business setting with LEDs providing close to actual sunlight all day long. The Sunlight Spectrum 2835 SMD packages are now available from the company.

    “We are pleased to introduce Hongli’s Sunlight Spectrum 2835, which is the perfect solution to those wanting very close to natural light from an artificial source,”

    “The Sunlight Spectrum 2835, which produces perfect colour, measuring more than 95 in the range R1 to R15 and continuous saturation, is very close to the actual sunlight spectrum. There is much less blue light, and it is a first choice for protecting our eyes.”

  4. Tomi Engdahl says:

    Implementing human-centric lighting

    The concept of human-centric lighting (HCL) has its origin in the discovery in the early 1920s that the human eye has a third type of receptor complementing cones and rods, which allow us to perceive color and light levels. Eyes are also equipped with photoreceptive retinal ganglion cells, which affect circadian rhythms. These cells communicate with the body’s center of physiological control and are especially sensitive to blue wavelengths of the visible light spectrum, which happens to be a significant component of sunlight.

    The 1980s saw the initiation of research into human biological response to light level and wavelength with investigations into the effects of lighting on mood, productivity, alertness, and visual acuity, as well as circadian rhythm. This research led us to the understanding that not all white light is equal, that cooler white vs. warmer white not only changes how we perceive our surroundings, but also affects our physiological responses.

    It’s no accident that upscale restaurants tend to be dimly lit with warm white light to both make our food (and us) look better and to encourage a sense of relaxation and leisure (perhaps leading to a higher tab).

    A concept intrinsic to HCL is varying the quality of illumination from light fixtures to mimic the different quality of natural light at different times during the day. LEDs are the first commonly available light sources that are adjustable–readily able to change both output spectrum and light level, which uniquely positions LEDs to optimize HCL in a wide range of facilities and environments.

    The most common application of HCL principles thus far is probably in air travel – it seems that all new commercial aircraft feature LED interior cabin lighting, often set to a pleasant purple hue.

    But it is in hospitals and assisted living centers that the potential of HCL is best realized so far.

    The potential for HCL to change our lives for the better is an exciting prospect, but it’s important to keep in mind that while there’s a general and growing consensus about how light spectra and levels affect the human body, individual results are impossible to predict. Nonetheless, according to BIS Research, the market for HCL products and systems is estimated to reach nearly $4 billion by 2024.

  5. Tomi Engdahl says:

    Arduino flicker meter-Determining the quality of light bulbs © GPL3+
    Numerous studies have shown that flickering, Although high frequency and then totally invisible, It can also cause headaches, eyestrain…

    Numerous studies have shown that flickering, Although high frequency and then totally invisible, It can also cause headaches, eyestrain and nausea. Commercial flickering measuring instruments are very expensive (from a few hundred to several thousand dollars), and we can make it for about ten dollars. The code is taken from Electronupdate blog, and instead of APDS9002 ligt sensor I use homemade sensor made of old transistor in metal box BC219. For a sensor you can use almost any transistor with a metal housing to which you will cut the upper part. I also use a 1.3 inch OLED display instead of 0.9 inches for better visibility, with minor code changes.

    The device is extremely simple to make and contains only a few components:

    - Arduino Nano Microcontroller

    - Small 1.3 inch Oled Display with SH 1106 chip

    - homemade Light sensor made of an old metal transistor

    - and one Button

    If we have an oscilloscope, there is a very simple way to test the flickering period and amplitude. All we have to do is connect the sensor directly to the scope without any additional electronics. Due to the nature of the experiment, the light during the shooting can change from very weak to very strong. We will first test the brightness of this battery flashlamp. As we can see, the signal is in the form of a straight line, which is logical considering that the LED is powered by direct current from the battery. Next we will test several types of light sources. I will present it to you in a very general and simplified way so that it can be better understood. In general, the closer the signal shape is to such a straight line, the better the lamp.

  6. Tomi Engdahl says:

    Anturit näkevät jo silmää paremmin

    Jo jonkin aikaa optiset anturit ovat kehittyneet niin nopeasti, että ne ylittävät ihmissilmän kyvyt. Anturit näkevät laajemman spektrin – myös näkyvää valoa – osaavat sovittautua esimerkiksi ledien vilkuntaan ja näkevät ihmissilmää paremmin hämärässä.

    STMicroeletronicsin VD6283-fotodiodi on tästä hyvä esimerkki. Anturi on kooltaan vain 1,83 x 1,0 x 0,55 millimetriä. Se aistii RGB-aallonpituuksia, mutta punaisen alueella näkökyky ulottuu ihmissilmää pidemmälle. Lisäksi herkkyys on parempi.

    Ledivalojen välkyntä on monella tapaa ongelmallista. Se aiheuttaa ongelmia teollisuuden konenäössä ja tutkimusten mukaan ihmisillä jopa pahoinvointia tai päänsärkyä. Siinä missä silmä voi aisti välkyntää 50 – 90 hertsin alueella, VD6283-piiri yltää herkkyydessä aina 2 kilohertsiin asti.

    Kun ledivalojen välkyntä tapahtuu tyypillisesti 100 – 500 hertsin alueella, ST:n piiri kykenee tunnistamaan ja suodattamaan pois sellaistakin vilkuntaa, jota ihmissilmä ei näe. Tämä on tärkeää, koska tutkimus on osoittanut, että myös ihmisen näkyvän valon ulkopuolella tapahtuva välkyntä voi aiheuttaa pahoinvointia.

  7. Tomi Engdahl says:

    Cheap LED screw bulbs are making our homes look gray and depressing

    If you buy an LED screw bulb, already the default on many store shelves, it will likely be a piece of junk presenting a low color spectrum and inferior longevity. The mix of colored diodes in the bulb will superficially appear to give out a white of a certain warmth or coolness, but the poor color index is revealed in the color of everything it lands on. With restrictions on incandescents kicking in, get ready for an indoor world that looks bleak, sickly and gray unless you’re prepared to fork out for expensive high-CRI bulbs. Speaking of which, manufacturers are happy to game (or lie) about Color Rendering Index: the 90+ CRI bulb you bought on Amazon is likely as bad if not worse than the honest crap you can get at the store.

    An interesting wrinkle for those with sleep quality problems: the blue diodes in LED light bulbs may be keeping you alert even when its hidden in the orange glow of a “warm” bulb. The simplest way to deal with this is to not use LED lights at all after sundown, but the science behind it is complex and up for argument.


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