LED lighting in theatres

StewartR

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Stewart
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#1
I have a friend who photographs theatrical productions. He gets problems with colour banding and colour variation, which we both agree is caused by the fact that his shutter speed is a fraction of the electrical mains frequency. He can't shoot at 1/50th, which would eliminate the issue, because of subject movement.

In the "old" days when theatres used tungsten lights, this issue was more manageable. Tungsten lights had a very predictable response to the AC cycle, and if he caught a shot at the "wrong" part of the cycle it would be under-exposed and possibly a bit too warm - both of which could sometimes be corrected if the shot was otherwise good and worth trying to save. However the situation with LEDs seems to be much more difficult. White LED light is created by using red, green and blue LEDs, and they seem to have slightly different electrical characteristics, so at different points in the AC cycle he's seeing variation in colour as well as variation in brightness.

Can anyone suggest a solution or a workaround?

Or failing that, can anyone point to a good source of information regarding the characteristics of the sorts of LED lights that are used in theatres, so that we can study it and look for possible workarounds ourselves?

Thanks for your help.
 
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Jim
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#2
Shoot at a shutter speed that does not divide by 50, helps but does not eliminate the issue or better still buy a 1DXII.

@KIPAX flickering lights indoors
 
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Steven
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#3
The only solution I can think of is using flash...
There are several camera models (Canon/Nikon/Sony etc) that have flicker reduction which attempts to synchronize the frame captures with the 100/120hz cycle. But it doesn't work consistently in dark settings (dark BG's), and it can delay the shot timing. I'm not sure it will be of much help for stage productions...

These are some of the limitations noted for the 7DII; they are essentially the same as listed by Nikon/Sony/etc.
"the shutter-release time lag may become slightly longer. Also, the continuous shooting speed may become slightly slower, and the shooting interval may become irregular."
"If the subject is against a dark background or if there is a bright light in the image, flicker may not be detected."
 
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Mark
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#4
Canon 7DIIs and 1DxIIs have an anti flicker setting. I can only assume that a couple of the modern Nikons might have something similar.

Honestly, that's your most practical approach.
 
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#6
I'm a bit surprised to hear this to be honest, where I've used LED source 4s I've been pretty impressed by their performance and lack of flicker.

So LEDs generally dim by being turned on and off very quickly, called Pulse Wave Modulation, so it depends on the speed that the fixture is doing that. If he is commissioned by the theatre, he may be able to ask the lighting designer to bring the overall exposure up - which would mean that the LEDs are 'off' for less of the time.
Higher quality fixtures may have RGBWW emitters rather than constructing the 'white' from RGB, which will usually be a cleaner colour and broader spectrum - LED red light always goes to poo when it's from a very limited wavelength, especially the red leds.

Sorry not to really offer a solution other than slower shutter speeds, and taking lots of frames!
 
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Brian
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#7
Dimming LED's seems to be a complex process.
itsdavedotnet is correct when he says LED's switch on and off rapidly, following the change of voltage due to the alternating mains voltage.
Conventional, filament bulbs also do this, but because of the thermal inertia of the filament, the brightness appears constant.
What is even more interesting is that modern cars with LED lights also flicker rapidly, despite apparently being fed from a DC voltage which, in theory, should be constant.

I had a light fitting at home that I wanted to install LED's into, which was also on a dimmer.
LED's are advertised as "Dimmable" or "Non -Dimmable" so I duly ordered the (more expensive) dimmable type.
When I fitted them I found the dimmer did not work, or at least worked just like an on/off switch.
When I read up on the subject, it seems that I not only needed dimmable LED's but I also needed a "trailing edge" dimmer.
So after still more expense changing the dimmer as well, I now have a dimmer controlled LED light fitting.
It's cost me quite a bit of money in order to save on my electricity bill!
I wonder how many years it will take for me to save the cost of the changes in reduced electricity use?
 
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