PWM Frequency

[meatpopsicle]

At a demo today for a major feature film I was called to the monitor to observe a flickering of the field of an LED batton on a backdrop. This was not the low level flickering of an LED going through the bottom of its curve but a "crawling of a line pattern across the backdrop.

Changing the camera shutter to 144 deg. fixed the problem (just as it would fix the flickering of an HMI that had a magnetic ballast or the line on a tv monitor).

My question is regarding PWM modulation frequencies. My understanding is that the LEDs are flickering at the frequency of their output ballast and if that isn't devisable into the shutter speed/angle, ie by 2 then more light ends up on alternating frames of film. Wouldn't a higher output frequency of the power supply fix this? Like Kino Flos? Is there a power conditioner that I can put on the line to increase the frequency coming out of the LEDs power supplies?

the fixture was a CK chroma force.

 

[derekleffew]

...the fixture was a CK chroma force.

You mean Chroma-Q Color Force?
A.C. Lighting - LEDs - Chroma-Q - Color Force 12
A.C. Lighting - LEDs - Chroma-Q Color Force

 

[epimetheus]

At a demo today for a major feature film I was called to the monitor to observe a flickering of the field of an LED batton on a backdrop. This was not the low level flickering of an LED going through the bottom of its curve but a "crawling of a line pattern across the backdrop.

Changing the camera shutter to 144 deg. fixed the problem (just as it would fix the flickering of an HMI that had a magnetic ballast or the line on a tv monitor).

My question is regarding PWM modulation frequencies. My understanding is that the LEDs are flickering at the frequency of their output ballast and if that isn't devisable into the shutter speed/angle, ie by 2 then more light ends up on alternating frames of film. Wouldn't a higher output frequency of the power supply fix this? Like Kino Flos? Is there a power conditioner that I can put on the line to increase the frequency coming out of the LEDs power supplies?

the fixture was a CK chroma force.

<Ignore>Short answer, no. The PWM frequency is set my the electronics within the device's power supply. There's not really anything you can do short of hacking up the unit and changing the power supply.</Ignore>

Never mind my above answer. The Color Force is one of those wonderful fixtures that has adjustable PWM frequencies. There's a menu option that allows you to change the PWM frequency to 600, 1200, or 2400. I would assume those values are in hertz, but the manual doesn't specify.