Odd effect... can anyone tell me why this looks this way?

skiahh

OK, so I was messing around with my wife's camera (Nikon D7000) after we finished the tree. I've always liked playing with a time exposure on the tree, just waving the camera around in a random pattern to get a "psychedelic" picture.

This was my first time doing this with both LED lights and with a DSLR, so I'm not sure which one caused the dashed lights. The tree lights are all steady; no blinkers.

The camera was set at f/10, 6" exposure, 18-55mm zoom set at 34mm (51mm FX equivalent, according to the EXIF), ISO autoset to 100.

I was surprised to see the dashed lights, like they were blinking or something. What caused this?

David_S85

They were blinking. Moving a camera (or subject) and electric power @ 60 cycles per second x 6 seconds time exposure = 360 dots per LED bulb.

ziggy53

Unlike a heated wire, as in traditional tungsten filament lights, LED lights will respond almost instantaneously to changes in voltage. It would appear that these lights are flashing, strobing really, but at a relatively high rate of speed (probably around 60 flashes/sec.). I suspect that they are being driven by an electronic circuit that has a bridge rectifier to convert the line voltage to pulsing DC, and also drops the line voltage and current to safe levels for the LEDs (a regulator).

You can confirm this flashing by using a higher shutter speed (I suggest 1/120th), in manual mode and with a fixed aperture, and shooting several images in rapid succession. The LEDs should be visibly dim in some of the exposures.

Here is someone who figured out a "flicker free" power supply for their LEDs:

http://www.techlib.com/area_50/barneysprojects.htm#Eliminate%20LED%20Flicker

I would not assume the the above circuit would work for your lights, but it shows you're not the only one to witness the phenomenon of LED flashing.

Edit: ... and David beat me to it.

skiahh

Ah, jeez... I should have known that.

Thanks, guys!