Led Hz

matt1

matt1

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Does anyone know what Hz my LED’s are likely to on a typical boat 12v DC system please? I’m trying to eliminate flicker in videos and understand that I need to adjust the camera frame rate to match the Hz of the lights.

I can find loads of info on typical US or UK AC Hz but not 12v DC and imagine they are different. Thx
 
The briefest of google searches told me that flicker is caused by imperfect screening/suppresson of mains frequency and most LED do so at f x 2 which would be 100Hz in this country. As your case is a 12v dc system on that basis there cannot be any
flicker unless you insert a dimmer perhaps. You'd have a very unusual camera indeed if it ran a frame rate of 100 fps.
 
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Most professional kit runs at a multiple of 300 to be ok for either 50 or 60 (technically 60000/1001).

If your LEDs aren't on an PWM dimmer, then they shouldn't flicker, have you checked the voltage isn't dipping?

If the flickering is constant, can you work out it's repetition frequency in the recorded video by stepping through frames. There's a relationship between flicker frequency, lighting frequency and frame rate.
 
It could be anything, or nothing, depending on how the manufacturer of the light fittings converted 12v DC to the lower voltage needed by the LEDSs themselves. The crude way would be a resistor which would cause no flicker, but wastes energy. Most other mehods involve turning the DC into AC at typically a fairly high frequency - whilst that might cause RF interference it probably would not cause visible flicker to a real video or film camera using a "shutter speed" of typically 1/48th of a second. If you are using a phone though for video it probably has a fixed wide aperture iris, so often "shutter speed" is tweaked up to quite high levels as a way of getting the image correctly exposed. This could cause flicker, and does cause all motion to look less smooth.
 
jwilson said:
It could be anything, or nothing, depending on how the manufacturer of the light fittings converted 12v DC to the lower voltage needed by the LEDSs themselves. The crude way would be a resistor which would cause no flicker, but wastes energy. Most other mehods involve turning the DC into AC at typically a fairly high frequency - whilst that might cause RF interference it probably would not cause visible flicker to a real video or film camera using a "shutter speed" of typically 1/48th of a second. If you are using a phone though for video it probably has a fixed wide aperture iris, so often "shutter speed" is tweaked up to quite high levels as a way of getting the image correctly exposed. This could cause flicker, and does cause all motion to look less smooth.
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If the frame rate and LED frequency are in synch (by the lights being a multiple of the frame rate), shutter speed shouldn't* matter - you're capturing the same part of the lighting curve each shutter opening. If they're out of synch, then you capture a different part of the curve each time.

*It will matter a small amount as the camera clock probably isn't locked so it won't be the correct frame rate. It will also matter if the lights are changing at less than the frame rate.

The short shutter speed is problematic though, it causes temporal aliasing, makes the image artificially sharper and causes some noise problems. All of which make it difficult to encode. Far better to add an ND and bring it down to normal levels.
 
12v LED lights run either by resistive current limiting usually by incorporating 3 actual diodes in series. (cheap for 12v only)
The sophisticated current control involves a high frequency switching to limit current and effectively transform voltage down. The clue here is that the fitting will be rated for voltage between 10 and 30v.
However the first type can have no flicker except voltage variations on incoming power and the second type will typically use frequency of around 100khz. I can't imagine any concern re flickering at that very high frequency. ol'will
 
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