How do I avoid horizontal banding when using LED strip lights for product photography?

Asked 11/14/2016

2 views

2 answers

0

I’m building recessed, diffused light boxes into the walls and ceiling of a small tabletop photo booth for consistent product photography. In testing, I’m seeing dark horizontal bands/stripes in my images. I usually shoot with an iPhone 7. What should I look for when choosing LED strip lighting to avoid this problem, and is LED strip lighting suitable for this kind of setup?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

9y ago

2 Answers

6

If I understand the question correctly (and I may well NOT be understanding it, in which case apologies for the useless answer! ;)):

This is usually caused by interference between the frequency at which the light oscillates and the speed of the rolling shutter in the camera. These days, most LED light systems are controlled by a PWM (pulse width modulation) controller, which cycles power on and off at a relatively fast rate to simulate variable brightness levels. In some cases the frequency of the cycling gets close to the frequency of the rolling shutter, which can cause problems.

The brighter the LEDs are with a PWM, the more time they spend "on" and the less time they spend "off". The dimmer the LEDs are with a PWM, the more time they spend "off" and the less time they spend "on". You will usually find that the interference patterns get worse with moderate to low frequencies.

There are two possible solutions. The first is to use a linear voltage regulator rather than a PWM to vary power to the LEDs. A linear voltage regulator is less efficient as it burns off the excess energy as heat, however it will not result in oscillations in the light intensity as a PWM does. Therefor, dimmer light is dimmer light, strait up.

The other option is to use an LC-filtered PWM. A filtered PWM will use an inductor (L) and capacitor (C) to maintain voltage and current in the moments when the PWM cycles off. You can usually find PWM controllers that are pre-built with filtration, however sometimes it's not specified. It is usually easier to find a linear regulator instead. Just make sure you use one that has a nice, large heatsink. ;)

I thought of a third option. Use a PWM that operates at a very high frequency. Something that operates at 15khz should avoid any problems with shutter interference.

Originally by user124. Source · Licensed CC BY-SA 4.0

user124

9y ago

0

AI Answer

Generated from our catalog & community — verify before relying on it.

The banding is typically caused by interaction between the camera’s rolling shutter and LED lights that are being dimmed with PWM (pulse-width modulation). The LEDs switch on and off very quickly, and the sensor records that cycling as horizontal dark bands.

To reduce or avoid it:

  • Avoid LED systems that use noticeable PWM dimming, especially at lower brightness.
  • If possible, run the LEDs at full power rather than dimmed.
  • Use a shutter speed long enough to cover the light’s full flicker cycle.
  • In the US, 1/60s or 1/30s are commonly suggested because they align better with mains-related flicker cycles.

If your camera app or camera gives manual shutter control, set shutter speed manually and test. With a phone, banding can be harder to control because shutter timing is often automatic.

Yes, LED strip lighting can work for a diffused product-lighting box, but choose strips/drivers with minimal flicker and test them with your actual camera before committing to the build.

UniqueBot

AI

9y ago

Your Answer