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Inside a Moving Head – Primer

The first in a series of articles about using modern intelligent lighting. This beginner’s guide to the moving light looks at common lighting effects and what’s inside the fixture itself.

When I started working with moving lights, the technology was fairly new and extremely mysterious. Now they have become cheaper, it seems like everyone had got access so some kind of intelligent light. Lighting techs are the kind of people that, given the chance, will rip the covers off any kit quicker than you can say “Leatherman”. But what if you are just starting out in lighting and don’t have access to any intelligent gear?

moving-head-gobo.jpg

What’s Inside a Moving Head?

Let’s look at what a moving head can do and the technology inside.

Light Source – Bright, efficient and even.

The light source in a moving head needs to be bright and efficient. Normal tungsten stage lighting lamps don’t fit the bill, so an arc lamp is used. Arc lamps require a special power supply (part of the fixture) and light source is not dimmable. Discharge lamps also generate a lot of heat and UV radiation – these are controlled by shields in the lamp housing. A reflector rounds up the photons and points them in the right direction.

Dimming / Intensity – Fading.

Stage lighting needs brightness/intensity control – dimming, if you like. Because the lamps (bulbs) in most moving lights can’t be dimmed electrically, a mechanical method is used. The dimming shutter on a moving head is simply a motor driven, metal mask that gradually cuts down the light output. Dimming shutters are mounted as far from the light source as possible, at the “front” of the head.

Strobe Shutter – Fast moving on/off switch.

Most moving lights also have a second shutter for strobe control, the rapid on/off action . The shutter strobe doesn’t dim, it just cuts out light. Very quickly.

Focus and Beam Control – The useful stuff that gives you control over the light output.

Even a 500w fresnel has some beam control, it’s what makes it useful. Moving spot fixtures have focus (sharpness) and/or zoom (bigger/smaller) functions, controlled in the usual manner – moving lenses. Spots also have Iris capability and some contain beam shaping shutters, which can cut off and angle edges remotely. Clever stuff.

Moving Wash or Beam lights (waggly PAR cans) give you the useful characteristics of a PAR lamp, beam width and oval angle (similar to spinning a normal PAR). These effects are created using glass frosts and adjustable brushed silk wheels within the fixture.

Colours – Changing colours without getting up a ladder

There are two kinds of colour control available in moving lights. Fixed colours and variable colour mixing. The two systems have pros and cons and many intelligent fixtures use both systems.

Fixed colour – Produced by one or more rotating colour wheels within the fixture. The light is filtered through special dichroic glass plates to produce the colour. Fixtures with 2 fixed colour wheels can overlay 2 dichroics, making a new colour using subtractive colour mixing. The advantage of fixed colour is that it provides good saturated colours such as Red and Dark Blue. The downsides are the limit to the number of colours available to the lighting designer. With a moving light “in view” (ie, on) the colours “clunk” don’t fade into place but clunk, often running through unwanted colours in the wheel.

Colour Mixing – A wide range of colours are produced using variable CMY subtractive colour mixing. Three gradiated colour “flags” are controlled to filter different amounts of the secondary visible light spectrum. The three colours Cyan, Magenta, Yellow when mixed in different quanties make a wide range of useful colours that can be faded into place. The down side to CMY colour mixing is there is some saturated colours it just can’t do.

Gobos – Old technology, great effects.

Gobos are still a great stage lighting effect and moving spot lights have gobos built in. One or more gobo wheels are hidden away inside, some rotating. A fixed gobo wheel is simply a large rotating plate with the gobo patterns punched around it. Rotating gobos are mounted in a more complex wheel that “indexes” (rotates) the gobo, as well as slotting a new one into the path of the beam. The gobo mechanism on a moving light is situated near the focal centre (the gate) and two gobo wheels can be laid on top of each other to get some interesting effects, especially with the focus function.

While there are many moving lights with “old fashioned” metal gobos inside, there are more advanced gobos around. Many are etched glass or dichroics that make coloured pictures possible, as well as much more intrictate designs. More slides than gobos, really.

Prisms and other Effects – With all that lot stuffed into a small casing, it’s a wonder there is room for more. Prisms that split the light into multiple beams, FX wheels and other bits and pieces. These lighting effects are based on traditional methods in stage lighting, automated and put into a moving head. Again, a relatively simple formula of motor driven moving parts.

What about actually moving this Moving Head, eh?

Ok, so you got to here and wondered why we hadn’t talked about this intelligent lighting actually moving. Well, I don’t know what to tell you. It moves. One motor makes it go side to side, the other motor up and down. The man on the street has gotten used to seeing waggly lighting, beams moving around doin’ stuff. “Robotic” lights are no longer interesting just because they look like magic. However, being able to direct a moving head to different points in space or make dynamic pictures in the air is powerful tool in your armoury.

So, now I know all about moving lights?

To use intelligent lights, you need to know what a moving head can do and how. As a user or operator, understanding the mechanics will enable you to get the most out of the equipment, the image at the top shows a reeded glass gobo, prism and colour given the soft focus treatment. All the little wheels, motors and bits of glass inside grind away inside creating looks that can be magical on the outside.

In the next part of the series, we will have a look at the more technical mechanics of a moving head with some pictures. If you have any questions or comments about this basic guide to moving heads, put them in comments box below.

14 Responses to Inside a Moving Head – Primer

  1. Alex Mead June 15, 2009 at 12:14 pm #

    Hi Rob,

    Great info here.

    Just wondering when the next part will come out – I think it would be really useful to know how to maintain + inspect movers; Take them apart etc… Often that gets overlooked when learning about lighting.

    Cheers,

    Alex Mead

  2. Rob Sayer June 19, 2009 at 4:13 pm #

    Hi Alex,

    Yes, another one “on the list”. I hope to get some guides like this out, although the time to write and illustrate this level of article is not something I have at the moment.

    It’s also tricky because the manufacturers do not often recommend servicing moving lights without training and experience in electro mechanical repairs. OSL tries to avoid promoting stuff that is against this advice.

    Thanks for your comment.

  3. Darcy Cook June 27, 2009 at 3:57 am #

    Hi Rob

    Just wondering if there is a correct procedure to shutting down a moving light rather than just flicking off the switch?

    Cheers

    Darce

  4. Rob Sayer June 27, 2009 at 6:44 pm #

    @Darcy – It’s considered best practice to Lamp Off the head, either remotely from desk or locally at the fixture, rather than just killing the power to the whole unit. Then the lamp gets to go through any powering down or cooling cycle, which could extend it’s life.

    Before the load out, it’s also friendly to “home” all the moving heads (i.e pan/tilt @ 50 / 50) so the crew just have to put the locks on and they are ready to go straight into boxes.

  5. Charlie July 9, 2009 at 10:30 am #

    Hi,
    I’m the lighting technician at a secondary school and need to discuss buying more lights with the HOD in a few days. I am very keen to but some moving heads, as they would make my life so much easier. At the moment, we only have conventional fresnels, par cans and fixed spots. We have no colour changing technology, and no LED lights. How would you recommend persuading the Head of Drama to spend the cash on moving heads?
    Thanks
    Charlie

  6. Rob Sayer July 9, 2009 at 2:25 pm #

    Hi Charlie. This is quite a common question over at the Blue Room. The common answer is probably one you won’t like much. I (and most lighting professionals) don’t advise secondary schools, even with well appointed performance venues, to buy moving lights.

    Moving lights bring new levels of expense, maintenance and complexity that a school can’t cope with. And moving light technology and fashions change quicker than schools turn over their equipment.

    I can’t think of one situation where, given thousands of pounds to spend on new kit for a school, I even consider splashing out on such hi tech kit. Schools always need more fresnels, lighting positions, dimmers and other much more useful stuff.

    If you want to play with the latest kit, hire it in.

  7. Rafael October 31, 2009 at 10:59 pm #

    So, please help me to understand, why there is a dimmer and a shutter if they do the same job?
    I understand that you need to have both controls,but it doesn’t make sense for me why the ML have both.

  8. Rob Sayer November 1, 2009 at 9:12 am #

    Hi Rafael, that’s a good question.
    The dimming shutter is designed to simulate a dimmer fade mechanically. You can snap it shut but there a limit to how many times a second this can happen.
    The strobe shutter is simpler and doesn’t provide dimming, it just opens and shuts. Quick enough to do strobe effects.
    Thanks for visiting.

  9. Michael November 8, 2009 at 4:30 pm #

    I have a question that I am hoping you can help me with… I have 8 intelligent lighting fixtures in my facility (a high school) 6 moving heads and 2 scanners and a small control board for the lights (all the same manufacture) – I have had the two scanners and the board for 6 years, and just acquired the 6 moving heads. I have programmed about 100 scenes for which I am using in my current production (along side a very nice package of traditional theatrical lighting), but just recently the scanners have just been “freaking” out without provocation… rapidly going through a whole series of rapid movements and color changes. The problem is – outside of the production, I have not been able to re-produce that “freaking” out situation – so I haven’t been able to identify why it happens. My first thought was a break or change in power, but I have made sure that is not it. I was also thinking that it might be the signal from the board to the lights being interrupted… but I also have not been able to re-produce that. It does not happen at the same time… no pattern to it occurring. Do I need a signal boost on a DMX line? Is that possible why it is happening? Please let me know where I can check next… I want to learn.

    Thanks,

  10. Rob Sayer November 18, 2009 at 8:05 am #

    Hi Michael,
    There is some more information on DMX and DMX Faults here at On Stage Lighting. However, if you only experience these problems when running your show cues it is more likely to be a programming error where unwanted control channels are being recorded with the wrong settings. Two other suggestions are the fixture mode / fixture personality issues or overlapping DMX addresses.
    Least likely in these situations is a fixture fault itself.
    Thanks for your question.

  11. John II February 17, 2010 at 5:27 am #

    Hi: In a theater production play, I’ve seen lighting and audio controllers out front in the audience that are controlling the steerable lights and punching up the audio tracks for live performances. The steerable lights are synced to the sound tracks, but can be over ridden when needed. Can you point me at some web sites that sell the digital equipment that they are using for this type of work ? For instant the Fostex LR16, claims you can have 16 music tracks or sound tracks recorded on it, and it has all the standard time code outputs for syncing it with other video or audio equipment including stage lighting, but what kind of lighting controller could you connect to it, to plan out all the moving lights for a particular sound track ? Anyone pointing me in the right direction would be dearly appreciated… thanks

  12. DuncanM July 2, 2010 at 5:21 am #

    Hi – to Michael. I’ve had this happen in my own shows. Thetrical programming is a lot different than concert programming eg trying to reduce fixture noise in the quiet bits! Two other options to consider are intermittent power supply faults ie wobbly/loose leads provoking a re-boot; and as Rob said, programming issues, particularly a dodgy cue with some odd-ball instructions, or a move between cues that involves a lot of changes (position, colour etc) between the two states. Solution for the second one, which is always happening to me, is to add another cue which kills the output so you can move the fixture without displaying the nasty flickering to the audience.

    to John II: consider MIDI as a possible solution. Many modern desks can output MIDI, which can be used to control/trigger other MIDI-capable devices. Me and my sound guy have many happy hours trying to control each other’s desks! Ah, happy memories…

  13. linlay Dodin May 12, 2011 at 7:08 am #

    Hi, i am a light designer from mauritius . We have a new studio since 1 month equipped with 12, 1200w moving head here we r new to that . could you give me some tips how to use it and how to create efx… thanx

  14. Djvex April 20, 2013 at 10:45 pm #

    when unit is switched to 14ch it pans smooth when set to auto or sound controlled…. when set to 8ch it sounds like an old zipper…Intimidator led 350 moving head. unit pans rough and slow, random … everything else works fine i.e. tilt , gobos…. I’ve tried troubleshooting tips in the manual but still no luck… maybe you could help

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