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?
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.