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Author Topic: Stage Lighting WITHOUT Dimmers  (Read 1685 times)

Mark Morley

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Re: Stage Lighting WITHOUT Dimmers
« Reply #20 on: February 15, 2021, 10:21:39 am »

With the advances in moving lights and controls I was wondering if one could set up a small stage lighting system without employing any dimmers, just by DMX control and some fixtures.. moving or fixed (scanners?).  I understand in many new fixtures dimming is internal as part of the DMX control system.  Since the lights are full on all the time I realize that power consumption is still a major consideration.  I am just thinking about simplifying the system design.
Although I am commercially linked to an audio distributor, I have no commercial links to lighting manufacturers - but have spent nearly 40 years designing and installing stage lighting systems. LED lights are pretty ubiquitous now - and you can theoretically run a large number from a 13A socket. A good quality 100W LED stage light outputs approx the same amount of light (or more) as an old-fashioned 1kW incandescent (lamped) stage light. Good-quality LEDs utilise RGBA (Red/Green/Bue/Amber) LED elements, which enables the user to get any colour they like by judicious mixing of each colour's intensity. Even better are those models which include additional colours, such as Lime and additional White LEDs - these enrich the palette and enable really pleasant Whites (RGB Luminaires rarely produce a clean white light, RGBA are much better at it). Some LED lights have seven or more different coloured LED elements.
Four issues to beware of:
1): don't buy cheap! Cheap LED lights are usually unreliable and won't deliver bright enough light. They can also be VERY noisy (cheap cooling fans). You should be prepared to spend at least 500 or 600 per unit for basic wash-lights, depending upon your intended usage (basic disco lighting much cheaper). Good-quality lensed stage lights start at 800 (plus VAT) or so for Fresnels, moving up to 1,500+ for profiles. Professional-use lights cost from 1,500 upwards. LED stage lights are also available with electronic focus and, of course, moving lights offer electronically-operated pan, tilt, gobos, prisms and more.
2): Beware RCD (Residual Current Device - or Earth-Leakage Trip) issues. Each LED light bleeds power back to EARTH ("Earth-Leakage") through its electronics. Good quality manufacturers quote earth-leakage data in their literature. Any RCD protecting stage or disco lighting should be rated 30mA. According to the HSE, a 30mA electric shock is "rarely fatal" - whereas a 100mA shock is usually fatal. An old fashioned 500W stage light is rated at 2.17A (@230V) - a shock at that rating is pretty much guaranteed electrocution (ie: DEATH by electric shock)! So - if your system is protected by a 30mA RCD and you connect lots of LED lights to it - it may trip-out, if the lights' combined earth-leakage gets near to or exceeds 30mA. Make sure you spread the lights between different RCDs.
3): INRUSH. All LED lights draw INRUSH currents when they are initially switched on. This is a momentarily very high surge of power (20A-50A or so). It only occurs for milliseconds - but if the MCB (Magnetic Circuit-Breaker) or RCBO (a combination of RCD and MCB) protecting that mains circuit is the wrong type and cannot cope with such surges, it will trip-out. Good practice is to switch each LED fixture on one-at-a-time, to minimise the Inrush power-draw. Once again - don't have too many LED lights on a single power-circuit.
4): WEIGHT. LED lights are MUCH heavier than the old-fashioned lamped stage lights they replace. An LED PARcan will typically weigh 5kg or more. Be careful, therefore, if hanging your kit from lightweight lighting tripod stands, or overhead lighting bars, that were designed for use with lamped lighting. Check the SWL (Safe Working Load) that a stand or lighting bar is rated at. Simply replacing ten old lights with ten new LEDs could put your equipment under too much strain.

DIMMERS HAVE DISAPPEARED? Yes (well, they're disappearing). No manufacturer is putting any more R&D into traditional dimmer development. Many new entertainment venues are being designed without any dimmers at all. HOWEVER, in large venues, dimmers are being replaced by banks of electronically triggered relays (an electronic power switch). The system remotely switches these relays on (or off) in a cascaded manner, so that inrush problems are avoided.

ALWAYS SWITCH OFF YOUR LEDS WHEN NOT IN-USE: I have visited venues (on maintenance duties), where LED stage lights have been left on for several months non-stop. Although there is very little heat in the light beam produced by LED lights, the fixtures themselves get quite hot - and most have an integral cooling-fan or two. If left on for weeks and weeks, these cooling fans suck in dust, which settles onto the electronic cards (a dust duvet). This prevents the unit from cooling-down, leading to component failure.
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Bob Rhead

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Re: Stage Lighting WITHOUT Dimmers
« Reply #21 on: February 28, 2021, 10:23:34 am »

Thanks Mark, great advice appreciated...I am of the same mind on quality gear and never buy based on price only. I was unaware of the RC issues... is this unique to LED fixtures.. I don't recall the term from when I worked in theatre.  Where would an RCD device go.. between the wall outlet and the fixture device chain?
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Bob Rhead

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Re: Stage Lighting WITHOUT Dimmers
« Reply #22 on: February 28, 2021, 10:38:32 am »

OK I understand RCD.. just hadn't heard it referred to in those terms.. basically like Ground Fault Interupters.  I didn't know that LED fixtures bleed some voltage into the grounds.. Great to know this is an issue to consider.
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Jeff Lelko

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Re: Stage Lighting WITHOUT Dimmers
« Reply #23 on: February 28, 2021, 06:38:58 pm »

I didn't know that LED fixtures bleed some voltage into the grounds.. Great to know this is an issue to consider.

While I can't speak as an electrician and have never tried to measure something like this, I've never once had any sort of issue with a properly-operating fixture bleeding power into the ground.  Mark, can you provide us some literature on this to substantiate your claim?
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Scott Hofmann

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Re: Stage Lighting WITHOUT Dimmers
« Reply #24 on: March 02, 2021, 02:38:50 pm »

While I can't speak as an electrician and have never tried to measure something like this, I've never once had any sort of issue with a properly-operating fixture bleeding power into the ground.  Mark, can you provide us some literature on this to substantiate your claim?
Seven or eight years ago I installed a dozen Elation IP65 fixtures outdoors at a city park; four metal poles with 3 fixtures per pole and all 12 were fed from one 20A GFCI breaker. Once we got past adding a certain number of fixtures, the GFCI would trip. The electricians removed the GFCI, installed a regular breaker, and did something to ground each metal pole as I recall, although the details are hazy. I do know they did agree that the GFCI was the problem. So I do think it had something to do with leakage current.
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Scott Hofmann

Paul G. OBrien

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Re: Stage Lighting WITHOUT Dimmers
« Reply #25 on: March 02, 2021, 07:30:46 pm »

4): WEIGHT. LED lights are MUCH heavier than the old-fashioned lamped stage lights they replace.

This is debatable, IP65 led fixtures can be weighty but IP20 no so much, and once the weight of the power cables needed to feed a string of halogens is factored in I think the LED option comes out lighter.
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Brian Jojade

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Re: Stage Lighting WITHOUT Dimmers
« Reply #26 on: March 02, 2021, 07:49:35 pm »

Seven or eight years ago I installed a dozen Elation IP65 fixtures outdoors at a city park; four metal poles with 3 fixtures per pole and all 12 were fed from one 20A GFCI breaker. Once we got past adding a certain number of fixtures, the GFCI would trip. The electricians removed the GFCI, installed a regular breaker, and did something to ground each metal pole as I recall, although the details are hazy. I do know they did agree that the GFCI was the problem. So I do think it had something to do with leakage current.
Any device leaks some current, but a properly working one should not trip a breaker.  However, as you multiply devices, the amount of leakage can add up to the point that it trips the GFCI. Even things like long extension cords build up capacitance that results in current leakage.  A 200' extension cord on a GFCI circuit will often trip.

Removing GFCI breakers is not a good idea, especially in an outdoor environment.  Grounding the pole does very little to help against the type of faults that a GFCI breaker would be protecting against.  Yeah, if the chassis became completely hot, it could draw enough current to trip a breaker, but it's the partial failures that will sneak up on you.

Eg, if a fixture gets wet, current leakage can exist. If the water then finds a path to ground through someone's body, that's when bad things happen.  For example, if you go to work on that fixture and have to remove it from the pole, the leakage current now would go through you right into that wonderfully grounded pole.  Not a good situation at all!

A better solution would be to split the lights up into multiple separate circuits with a GFCI closer to where protection needs to be.  Yes, the main wire from the circuit breaker won't be on GFCI, but all of the devices downstream would be, and would then be able to provide protection.
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Brian Jojade

Jeff Lelko

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Re: Stage Lighting WITHOUT Dimmers
« Reply #27 on: March 02, 2021, 09:10:25 pm »

Any device leaks some current, but a properly working one should not trip a breaker. 

I agree, and I also agree that in real world use cases there are many reasons why some current may leak out the ground (hence why it exists).  My argument is that I've never seen this spec'd as a design feature as opposed to an incidental occurrence.  Even ETC - arguably one of the most reputable manufacturers of LED stage lighting - does not include any such statement in their literature.

This is debatable, IP65 led fixtures can be weighty but IP20 no so much, and once the weight of the power cables needed to feed a string of halogens is factored in I think the LED option comes out lighter.

I agree with this too - especially if the dimmers end up in the rigging!  Mr. Morley might not yet be familiar with the ProSoundWeb trademark "it depends", along with the fact that sweeping generalizations are difficult to defend.

Good-quality LEDs utilise RGBA (Red/Green/Bue/Amber) LED elements, which enables the user to get any colour they like by judicious mixing of each colour's intensity.

I'll throw another "it depends" in here too.  ETC has had excellent success with the RGBL mixture in many of their product lines.  While adding discrete color elements to an array never hurts, it's only one factor contributing to how "good" a fixture's output will be.  Other factors such as CRI, refresh rate, and low-level performance play just as big a part as how the manufacturer chooses to mix colors.   
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ProSoundWeb Community

Re: Stage Lighting WITHOUT Dimmers
« Reply #27 on: March 02, 2021, 09:10:25 pm »


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