disappearing led light
Apr 17, 2016 21:52:46 #
wer224
Loc: Bergen county NewJersey
hi all, i have a canon 7dm2, today i was just playing with the white balance shift, in camera and noticed something, hoping anyone can elaborate on what i saw. i was in my kitchen and took eleven pics in the cameras high speed capture with no flash. In the eleven shots which took just over one second i noticed a blue led night light going from full brilliance in the first pic to no illumination at all in the last pic. i'm assuming it has to do with the 60 cycles in the ac sign wave. hopefully the three of the 11 pics i added i did correctly so you can see it, (1st 5th and last in the series) if so the blue led light is on the left of pics. is this this the same premus as fluorescent lighting has on flashless photography. or is my house possesed :) wondering what all the new led bulbs commimg out what will this do to flashless photography. thanks for any input info on this. bill
Apr 17, 2016 21:57:49 #
Not sure what's going on. I was under the assumption that LED's were continuous & not affected by AC current. They have a driver circuit included that converts AC to DC.
Apr 17, 2016 22:19:53 #
LED are true DC Voltage. They are continuous out put.Th photo LED units are converted from AC to DC voltage. It looks like you have a Night Light which may not be a true LED.
wer224 wrote:
hi all, i have a canon 7dm2, today i was just play... (show quote)
Apr 17, 2016 22:20:13 #
nicksr1125 wrote:
Not sure what's going on. I was under the assumption that LED's were continuous & not affected by AC current. They have a driver circuit included that converts AC to DC.
It has been my experience that some LEDs do "pulse". I would imagine that those designed for photography are different. I don't use them, so I can't swear to that-- but I do have an LED desk "spot" light that acts this way.
Apr 18, 2016 00:01:32 #
If I remember my electronics correctly and they went cheap on the AC to DC conversion and only did half wave, then the LED would pulse.
Apr 18, 2016 01:04:07 #
KM6VV
Loc: Central Coast, CA
wer224 wrote:
hi all, i have a canon 7dm2, today i was just play... (show quote)
That's interesting. What rate were you shooting at?
As I think has been stated, LEDs are similar to diodes, and require DC current. The simplest AC-DC conversion is a half-wave conversion, and the DC will pulse. Even full-wave (both halves of the AC cycle) will a pulsing DC, unless it is filtered with a capacitor. I wouldn't think you'd capture just a half-cycle, unless your shutter was quite fast. What shutter speed?
Apr 18, 2016 05:14:31 #
KM6VV wrote:
That's interesting. What rate were you shooting at?
As I think has been stated, LEDs are similar to diodes, and require DC current. The simplest AC-DC conversion is a half-wave conversion, and the DC will pulse. Even full-wave (both halves of the AC cycle) will a pulsing DC, unless it is filtered with a capacitor. I wouldn't think you'd capture just a half-cycle, unless your shutter was quite fast. What shutter speed?
As I think has been stated, LEDs are similar to diodes, and require DC current. The simplest AC-DC conversion is a half-wave conversion, and the DC will pulse. Even full-wave (both halves of the AC cycle) will a pulsing DC, unless it is filtered with a capacitor. I wouldn't think you'd capture just a half-cycle, unless your shutter was quite fast. What shutter speed?
LED Light Emitting Diode , not just similar :)
Apr 18, 2016 05:28:31 #
wer224 wrote:
hi all, i have a canon 7dm2, today i was just play... (show quote)
There's a flicker detection function in the menu of the 7D2-this is for the "pulses" of flourescent lighting. Try actuating that function and see what happens.
Apr 18, 2016 05:41:16 #
LED do pulse if you want them to. They can pulse fast. I think those cheap light just rectifies the AC current half wave so that there is no power half of the AC cycle.
Apr 18, 2016 06:09:39 #
nicksr1125 wrote:
Not sure what's going on. I was under the assumption that LED's were continuous & not affected by AC current. They have a driver circuit included that converts AC to DC.
The alternator in your car produces AC which is then converted to DC via diodes. It is not pure DC, but rather pulsating DC due to the fact that the diodes only stop current flow in one direction. I would imagine that the same effect is at work with most common LEDs.
One easy way to check: The Canon 7DII has flicker detection capability. Take 2 sets of photos, one with and one without that feature turned on and compare the results. I may have to try that later, once my morning coffee works its magic!
Apr 18, 2016 06:11:56 #
wer224 wrote:
hi all, i have a canon 7dm2, today i was just play... (show quote)
Could be you're capturing it when it's on and off if your shutter speed is fast enough. That seems to be the new, hip thing: LEDs that flicker very fast. I've noticed them on some of the newer taillights on cars. Perhaps that's what you're seeing. I guess it's to save energy? I know they're annoying on my eyes because I can see the flickering if I move my eyes across them fast enough.
Apr 18, 2016 06:47:50 #
Shoeless_Photographer wrote:
...I can see the flickering if I move my eyes across them fast enough.
Yes, that is a strange effect. I've noticed something similar on my monitor if I look at it with my peripheral vision.
Apr 18, 2016 07:01:42 #
Cheapest construction would be a diode, resistor, & LED. These will flicker due to the rectified sine wave when the voltage hits zero. But your eye can't see it due to the eye's image retention characteristics. You eye and usually will not see the increase/decrease in brightness (60 Hz). A single diode will yield half wave rectification- off 50% of the time, intensity increases until full voltage at the peak of the sine wave. The camera shutter, if fast enough, at the right part of the cycle, could catch the LED with zero power to it.
Apr 18, 2016 07:08:21 #
You just happened to catch the led in a pulse mode.
Those things can pulse so fast you'll never be able to visibly see it happen if the designer makes it so. They can use led lights for communicating if they want. (It's faster and under some conditions, can be more reliable that wires.
Those things can pulse so fast you'll never be able to visibly see it happen if the designer makes it so. They can use led lights for communicating if they want. (It's faster and under some conditions, can be more reliable that wires.
Apr 18, 2016 07:51:56 #
GENorkus wrote:
You just happened to catch the led in a pulse mode.
Those things can pulse so fast you'll never be able to visibly see it happen if the designer makes it so. They can use led lights for communicating if they want. (It's faster and under some conditions, can be more reliable that wires.
Those things can pulse so fast you'll never be able to visibly see it happen if the designer makes it so. They can use led lights for communicating if they want. (It's faster and under some conditions, can be more reliable that wires.
:thumbup:
qv. fiber optics
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