cyclespeed Loc: Calgary, Alberta Canada

In live view using my Sony a6000 I focused on the foreground expecting to see the Bokeh effect in the LED lights in the background. The ss was set at 1/15. The lcd showed a black screen that had a rising curtain starting at the bottom and moving to the top. Following the curtain was a screen full of the Bokeh lights. Once they reached the top the screen it would be all black again and the rising curtain effect would begin Once more. If I changed the ss to 1/60 or faster no moving curtain was detected and the lights were displayed in a normal way.
I know LED's use a very rapid on off technology but does that somehow make the exposure have this sequence?
I did need the ss of 1/15 to get enough light on the foreground subject so I just waited until all the bokeh scene was in the lcd display before taking the picture.
Can you explain this phenomenon? Thanks for your insights.

blackest Loc: Ireland

Leitz Loc: Solms

Bokeh scene???

Nymphadora

Wow...!! That's amazing. Nyms

blackest Loc: Ireland

t's fairly straight forward diodes and that includes light emitting diodes only pass current in 1 direction from the anode to the cathode + to -

your lights are a bunch of Leds in series connected to an AC supply on an oscilloscope this is a sine wave pattern. looks like a circle but the top half is off set to the bottom its generated that way with a rotating coil in a magnetic field at the power station.

so if you plot the voltage it builds from 0v to +120v falls back to 0 volts and then down to -120volts and back up to 0 this happens 60 times a second. So it is only conducting in the right direction for half the cycle for the diode so if you measured voltage across the diode it would be a half circle followed by 0 volts and then the half circle again.

1/60th of a second is enough time to catch a whole cycle 1/15th is 4/60ths so should catch 4 cycles hmmm,

The other thing is the diodes need 0.7 of a volt to conduct and about 1.5 to reach maximum brightness each led will be dropping 0.7 of a volt before they turn on so for the positive half cycle they should be on for about half of it. So 3/4 of the time your leds are effectively off.

However thinking about things at 1/15th you get 4 complete cycles and at 1/60th just one cycle. With a mechanical shutter it would be wide open for the 4 cycles and the exposure would be the same over all.

I think it is actually due to the electronic shutter measuring the sensor at different times but i'm not so sure now.

Bull-Dozer Loc: Vermont

I am thinking that most Christmas tree lights would have a "full wave DC converter" so the actual frequency would be 120 Hertz. So the LEDs would be on twice as long.

rehess Loc: South Bend, Indiana, USA

This is a fascinating question, and I'm guessing that there are several aspects to it. Most of the discussion has been about how the lights behave, but it seems to me that part of the question is about how the camera builds an image for the LCD / EVF.

The only mechanical shutter on my smaller Pentax Q-7 is the leaf shutter in its lens. The K-to-Q adapter sold by Pentax also has a shutter, but the cheaper adapters provide no mechanical shutter. It turns out that reading the sensor actually takes something like 1/15-th second regardless of the specified "shutter speed", so using those cheaper adapters can result in the famed "rolling shutter" effect. I'm wondering if something similar is at work in your camera - that because of the blinking already mentioned, the software has to read the shutter multiple times in order to make sense of what it is detecting.