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LED - dimmers vs. shutters?
Old 8th February 2020
  #1
LED - dimmers vs. shutters?

Some LED based fixtures have a dimmer and shutter channel, example would be the intimidator series by chauvet or superfly by cameo etc.

Now I wonder:

Are those two channels doing basically the same or are there differences?

For example: Low frequency strobes (like every beat) could be done by either setting dimmer to full-on and let the shutter do the blinkenlights or vice versa.

I get the idea of using a shutter channel for fast strobe effects (save bandwidth on the DMX bus, as it is a single message instead of dozens per second). But for slow on/off operations, does it make a difference, such as reaction speed or wear and tear on the LEDs?

I guess it all comes down to whether there is a real shutter part or if the shutter channel just controls the brightness of the LED and is basically a remapped dimmer. Not exactly sure what "electronic shutter" means, if that is a separate element in the circuit or just a software function to emulate physical shutters. Unfortunately, most manuals are not very clear on that.

Can someone point me in the right direction?
Old 8th February 2020
  #2
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An electronic shutter would just be turning the LED on and off. I rather doubt many LED fixture would have a physical shutter for light control; some may have one for protection from e.g. direct sunlight exposure if they have well-focused optics (which, of course, work in reverse very well as little solar furnaces). A mechanical iris is a possibility for beam shaping, but that's not generally considered a shutter even if it can close all the way.

There's no real wear and tear difference on the LED to turn it on and off vs. leaving it on. For that matter, dimming on LED fixtures is invariably done using PWM circuitry--turning it on and off in varying amounts thousands of times a second. They also respond quite quickly, limited mainly by how quickly phosphors respond for LEDS that use phosphors (mainly white ones; LEDs themselves are inherently monochromatic, so white LEDs use various phosphors to absorb some of the radiated light and re-radiate it in other colors).

You aren't saving any DMX bandwidth by using a shutter channel in preference to a dimmer channel. All DMX channel levels get sent with every DMX packet. It's not like MIDI where there are individual events that get sent; it's a fresh dump of the state of everything each time. For fast strobes, using a fixture's built-in strobe feature--if it has one--will probably give a better effect since the DMX refresh limits the speed possible for strobes directly controlled by it, as the fixture's little computer brain isn't limited by DMX refresh speeds, but doesn't affect the DMX bus bandwidth or utilization.
Old 9th February 2020 | Show parent
  #3
Top, many thanks for the clear explanation!

Regarding shutter effects and bandwidth, I meant the same thing but didn´t use the right words I guess.

Using the shutter channel gives me 0 = closed, 255 = opened and in between there are ranges for just strobing, 8 = slow to 76 = fast, next range for pulsed strobes etc. Using one of those "strobe modes" can be achieved by a single DMX message.

So for shutter it depends, whether you use "external strobe" via DMX using 0 and 255 only - or using "internal strobe" with one of the pre-programmed options (which are hard to sync, but there is always something...)

Achieving the same via the dimmer channel with the shutter open all the time would also call for multiple messages.

Coming back to my original question: I guess I will keep the dimmer full-on and do everything via the shutter channel. While the dimmer data get´s transmitted anyway with every message, it doesn´t make a big difference, but doing the same task on the same channel keeps things together. At least it´s easier to remember for me.

Now that I´ve learnt the background, it makes sense for me to think of the shutter as the on/off channel and see the dimmer as "just for intensity". Well it was in the names from beginning, but now it´s much clearer and I have peace of mind regarding unwanted side effects which aren´t present.

Thank you again!
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