MACT Loc: Connecticut

I am using LED bulbs while making multiple exposures for focus stacking, and have run into a problem. The images go through a cycle, starting fine, getting progressively darker for 3-4 shots, then getting lighter for 3-4 shots. This cycling continues throughout the sequence. Does anyone have an explanation/solution for the effect?

Thanks

Dan Downie Loc: Rochester, NY

I have no idea what could be causing the problem, but I look forward to the responses you get. Good luck!

TriX Loc: Raleigh, NC

Do you have exposure bracketing enabled, perhaps inadvertently?

OddJobber Loc: Portland, OR

LED lights do flicker. Slower shutter maybe?

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Try using a shutter speed that is equal to or shorter than 1/100.

Mustanger Loc: Grants Pass, Oregon USA

LED lights are not the perfect answer by any means. I discovered you cannot just go changing them to brighter (higher wattage rating) willy nilly thinking it compares directly to incandescent lighting! LEDs cause switches to have a derated ampere rating due to I think a much higher inrush current as they fire up & with AC they are constantly rising & falling. I finally saw a derated LED switch that listed 500 watts incandescent & only 325 Watts LED. It explained why I was losing wall switches every 6 months or so. Plus the flickering has made some people sick, nauseous, or induced seizures.

This is not a perfect explanation but even electrical engineers are having difficulty explaining why LEDS have this problem...I do not understand electrical harmonics! Dimmers are especially sensitive, Different brands respond differently some never completely shut off the lights completely! A faint glow is visible at night.

Mike Adams Loc: Connecticut

Thanks for the suggestions. I will try a faster shutter speed to see if that eliminates the problem. I am still not clear why it would cycle unless the time between shots was precisely offsetting the next one by essentially 1/8 the time between pulses in the LED (thus bringing it back in synch every 8 shots). Testing this would need need equipment I don't have access to.

sippyjug104 Loc: Missouri

There is quite a difference between Tube flash and LED flash in their "firing time" and the result of the image will show the difference due to the physics of the two. A Tube flash reacts to the speed of electricity which is near the speed of light so it is nearly instantaneous each time. The LED has to receive the same electric signal and then it has to react to make the diode emit light so it is not nearly as fast. I have both a Tube ring flash and an LED ring flash and I found that they perform much differently which requires me to use different shutter speeds between the two.

burkphoto Loc: High Point, NC

LEDs and CFLs and fluorescent tubes are not always flicker-free sources! You *can* get fixtures and lamps that don't flicker. They are made for photography and video, and are usually quite a bit more expensive than standard sources. Incandescent (quartz-halogen) lamps don't flicker either (and have continuous spectrum output). But incandescents suck wattage and produce lots of heat.

Our eyes don't see such flicker, but the camera can capture it when the shutter speed is too high, typically above 1/60 second in the USA, 1/50 in Europe. Try lowering your shutter speed to 1/30 and see what happens. Or, buy a camera with an "anti-flicker" feature (some of the high-end bodies actually have circuits that time the exposure sequence to avoid the flicker!).

You can test for flicker in a source... Set 1000 ISO, aperture priority, f/4, and photograph the light source in continuous mode. The resultant rapid sequence with a high shutter speed will show you the flicker, if there is any.

The phenomenon is caused by AC current. AC has two peaks in voltage — one positive, one negative — every 1/60 or 1/50 second. In between, the voltage is fluctuating across the zero point from positive to negative (and back on the next cycle). The darkness appears at the zero point, the lightness appears when there is peak voltage. Our eyes don't see it... but camera shutters do. Incandescents don't flicker because the filament stays hot enough for nearly constant output. LEDs and fluorescents can be made with persistent phosphors or other compounds that glow more consistently, and with ballasts that operate at higher frequencies, or circuitry that produces a less discontinuous output. But the cheapies just suck for photos and video!

It's even worse when you have a 277-volt commercial building fluorescent lighting circuit, for reasons I won't bore you with.

speters Loc: Grangeville/Idaho

Yep, don't use LED's! Or use only flicker free LED's ($$)!