3 ms·

LED flicker usually has nothing to do with AC power. They LED is being purposely driven pulsed to maximize power efficiency. Incidentally, incandescent bulbs f

LED flicker usually has nothing to do with AC power. They LED is being purposely driven pulsed to maximize power efficiency. Incidentally, incandescent bulbs flicker at 120 Hz (in the US) but it is imperceptible because the light output doesn’t go to zero and it is beyond the flicker fusion threshold (~60 Hz)

mrob 6y ago
Many cheap LEDs flicker at at double line frequency (100Hz or 120Hz depending on the country), because they're driven by rectified AC power with inadequate filtering. Pulsing LEDs only increases efficiency at low brightness, e.g. 7-segment displays, not room lighting. See: http://donklipstein.com/ledp.html http://donklipstein.com/ledp.html The flicker fusion threshold for many people is above 60Hz. Remember 60Hz CRTs? 85Hz is a more reliable threshold. And in any case, flicker fusion threshold is only relevant when your eyes are stationary. On eye movement you get phantom array effect. People vary greatly in how sensitive they are to this, and depending on how strong your saccadic masking is, it can be annoying at frequencies well into the kilohertz.
- blackguardx 6y ago
  The efficiency gains of pulsed drive isn’t in the LEDs, it is in the drive electronics.
  - mrob 6y ago
    How does pulsing at a frequency that's unrelated to the AC line frequency but still low enough to be visible improve efficiency? SMPS efficiency usually peaks in the hundreds of kHz, which is invisible even to the most sensitive observers.
    - blackguardx 6y ago
      I think we are saying the same thing.
      - mrob 6y ago
        You said "LED flicker usually has nothing to do with AC power." But most LED lighting flicker is the result of using a capacitive dropper power supply. These are cheap and efficient, but produce a lot of ripple at double the line frequency (with full-wave rectification). Filtering the output enough to make flicker imperceptible would cost more, and not everybody notices the flicker so it's easy to get away with cutting corners. See: http://www.bigclive.com/ledlmp.htm http://www.bigclive.com/ledlmp.htm Better and more expensive LED drivers use a switch mode power supply, which does not produce visible flicker.

mrob 6y ago

Many cheap LEDs flicker at at double line frequency (100Hz or 120Hz depending on the country), because they're driven by rectified AC power with inadequate filtering. Pulsing LEDs only increases efficiency at low brightness, e.g. 7-segment displays, not room lighting. See: http://donklipstein.com/ledp.html http://donklipstein.com/ledp.html The flicker fusion threshold for many people is above 60Hz. Remember 60Hz CRTs? 85Hz is a more reliable threshold. And in any case, flicker fusion threshold is only relevant when your eyes are stationary. On eye movement you get phantom array effect. People vary greatly in how sensitive they are to this, and depending on how strong your saccadic masking is, it can be annoying at frequencies well into the kilohertz.

blackguardx 6y ago
The efficiency gains of pulsed drive isn’t in the LEDs, it is in the drive electronics.
- mrob 6y ago
  How does pulsing at a frequency that's unrelated to the AC line frequency but still low enough to be visible improve efficiency? SMPS efficiency usually peaks in the hundreds of kHz, which is invisible even to the most sensitive observers.
  - blackguardx 6y ago
    I think we are saying the same thing.
    - mrob 6y ago
      You said "LED flicker usually has nothing to do with AC power." But most LED lighting flicker is the result of using a capacitive dropper power supply. These are cheap and efficient, but produce a lot of ripple at double the line frequency (with full-wave rectification). Filtering the output enough to make flicker imperceptible would cost more, and not everybody notices the flicker so it's easy to get away with cutting corners. See: http://www.bigclive.com/ledlmp.htm http://www.bigclive.com/ledlmp.htm Better and more expensive LED drivers use a switch mode power supply, which does not produce visible flicker.