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Long Run of RGB Chase Sequences for News Set


Joseph Tese
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Hello,

I'm helping with the design and lighting of a news set that will feature long runs of horizontal and vertical RGB chase sequences. There will be a long line of frosted plexiglass embedded into the wall that will be backlit with the lights.

I'm wondering what RGB lighting will provide good results, without also breaking the bank. Knowing it will be diffused heavily by the frosted glass, I'm curious if I need tight pixel control such as titan tubes, or if there are more cost effective options that don't have as "smooth" of a gradient. Obviously, these lights need the ability to daisy chain together with DMX to be seamless over a longer span.

I'm not trying to cheap out here, but knowing where these lights will live (behind frosted glass as a background element on a wall, vs Skin Tones) I'm also wondering if some lights more popular in the theatre/live event world will be suitable... or if I will run into color issues on camera.

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If you want to go really budget, there is, as you'll have realised, very inexpensive programmable LED strip which could potentially be used for something like this. The part number you're looking for is WS2812, which describes the tiny controller chip that's in each individual LED emitter. Various DMX and ArtNet-to-WS212 devices are available. This would be extremely inexpensive compared to almost any other imaginable way of doing it, it would fit easily inside almost any set piece and it would be fully programmable.

If you don't need it to be a beautiful keylight to make the talent look wonderful, which you don't, you could probably make it work. They may not end up looking on camera like they do in person, but that's fairly normal.

The concerns will be longevity and flicker. These things are based on individual red, green and blue emitters which generally have a longer life than white-emitting LEDs, and I would encourage any design for this sort of scenario to run the LEDs at no more than two thirds maximum power to extend their life, and that would go for an Astera tube or a length of WS2812 strip.

In a news studio sort of situation I would expect a good chance of avoiding flicker problems at conventional frame rates and shutter speeds. They look OK here:

 

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Along with Chroma-Q, Chauvet is an option as well. They have quite the selection of batten style fixtures. https://www.chauvetprofessional.com/products/category/batten-cyclorama/. Depending on your budget it might not be a bad idea to reach out to someone like 4Wall and see if they have anything used they are looking to off load. They have a website they sell on www.usedlighting.com but you can also give them a call and see what they have. 

If space is a premium the pixel tape option is a good one. Expanding on Phils mention of flicker, most pixel LED tape has a fixed PWM frequency and it is usually quite low. We have a WS2812B tape that has had issues with flicker on camera, I am not too sure about the other styles though.

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It may be worth adding that almost anything you can get from the theatre and live events world is likely to need careful testing for flicker, too.

As Harrison says, though, I wouldn't be entirely discouraged by that reality as it might be possible to save a really enormous amount of money and make yourself popular. In order to avoid wasting a really enormous amount of money and making yourself unpopular, proper testing for flicker will be required. I note this here because I've been caught out myself, but there are a few easy things to do which can make this easier.

Don't just point a camera at an open LED emitter. The actual emitters are extremely intense and likely to clip the camera, perhaps in strange ways depending on their colour, which can make subtle flicker hard to see (also you'll spend the next ten minutes seeing a little row of dots). Put them behind a diffuser of the type you're intending to use, or aim them at a diffusing surface, perhaps just a sheet of white paper.

Don't just rely on a monitor. Look at them on a monitor to detect banding on rolling-shutter cameras, if any, but also look at a waveform monitor as this makes flicker much easier to see as a bouncing in the waveform.

Check for long-term shutter phase problems. Frame up a shot, note where the exposure is on the waveform, and leave it like that, checking back every few minutes or so. This is mainly an issue on low-frequency lighting like iron-ballasted fluorescents or metal halide lights, often in 50Hz localities shooting frame rates near 24 which are almost half the mains frequency, but it's not impossible to imagine it here.

Don't test them at full power. Or rather do, but also test them at 25%, 50%, and 75% as well. At full power the pulse width modulation duty cycle may be 100%, which means they don't actually switch off at all, and thus won't flicker.

And naturally, test at whatever frame rates and shutter speeds you anticipate will be used. In a broadcast context this is likely to involve a discussion with a senior vision engineer. With something like WS2812, as Harrison says, you will very likely be able to find a setup which will make it flicker, probably at high shutter speeds.

A pain. But again, you could save a massive pile of gold.

P

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