Does anyone know, what's with the blinking LED's on the front and tail lights? I saw that in several videos (YouTube - Alfa Romeo Giulietta review by autocar.co.uk) and (YouTube - Alfa Romeo Giulietta), but nobody mentioned about it. Is there some kind of switch that activates the blinking?? I believe it is not a camera's rolling effect.
alpuras
G
Led lights flicker at a very high speed, too fast for human eyes to see... but a camera at 25 frames per second picks it up and makes them look as if they are blinking.
They're not.
They're not.
G
What's the reason for the LED flicker then? 
Technology-wise I can't think of a reason for it, unless they are strobing them
to give different intensity for fade on/off etc...
Technology-wise I can't think of a reason for it, unless they are strobing them
to give different intensity for fade on/off etc...
G
Science...
At a guess something to do with alternating currents, same reason flourescent lights flicker, tv's flicker, etc.
At a guess something to do with alternating currents, same reason flourescent lights flicker, tv's flicker, etc.
G
oops. good point.
Its called Pulse Width Modulation and is used to dim or intensify the output by pulsing the light, as led's dont react well and can vary in colour if the voltage is lowered.
Apparently.
Its called Pulse Width Modulation and is used to dim or intensify the output by pulsing the light, as led's dont react well and can vary in colour if the voltage is lowered.
Apparently.
OK well I may be able to help, my business makes LED displays. The benefit of multiplexing or flashing, typically at 60Hz + is that you can get away with using a lower rated power supply and lower rated components to drive the LED. So it reduces the cost. You also help prolong life of the LED by reducing heat buildup. Typically they are only 'on' for 1/8 of the time in our displays.
It is nothing to do with dimming. And LED's don't vary light output - they can only ever output a very specific narrow wavelength of light. Voltage to an LEd must be constant but varying forward current will change light output.
The earlier poster is correct that when filmed this gives a curious flashing / intermittent effect as the camera frame picks up the LED's in the array which aren't on at that exact moment. It is less noticeable in darker environments (longer shutter time). If you feel enthusiastic you can replicate this by spreading the fingers of one hand and waving it up & down rapidly in front of your eyes so you se a series of 'frames' separated by fingers. You will of course appear to be a total lunatic to any onlooker.
It is nothing to do with dimming. And LED's don't vary light output - they can only ever output a very specific narrow wavelength of light. Voltage to an LEd must be constant but varying forward current will change light output.
The earlier poster is correct that when filmed this gives a curious flashing / intermittent effect as the camera frame picks up the LED's in the array which aren't on at that exact moment. It is less noticeable in darker environments (longer shutter time). If you feel enthusiastic you can replicate this by spreading the fingers of one hand and waving it up & down rapidly in front of your eyes so you se a series of 'frames' separated by fingers. You will of course appear to be a total lunatic to any onlooker.
rhett, the flickering is indeed caused by PWM. To achieve a given level of light output, it's better to fit LEDs with much higher output, and then pulse them, rather than fit LEDs with the desired output and run them continuously. Pulsing allows the diodes time to cool, and so prolongs their working life.
As for how to fix it.. With a good quality video camera, you can remove the effect by choosing a slower shutter speed (and controlling exposure with a tighter aperture or a neutral-density filter over the lens), at the expense of some motion blur. On a phone camera, there's nothing you can do about it generally - I've never seen a phone camera with video shutter speed control (although the best cameras like Nokia's will allow shutter speed control for stills)
As for how to fix it.. With a good quality video camera, you can remove the effect by choosing a slower shutter speed (and controlling exposure with a tighter aperture or a neutral-density filter over the lens), at the expense of some motion blur. On a phone camera, there's nothing you can do about it generally - I've never seen a phone camera with video shutter speed control (although the best cameras like Nokia's will allow shutter speed control for stills)
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