Moving head lights belong to a group of equipment known as 'intelligent lights'. These are distinguished from ordinary, non-intelligent lights (named 'generics') by the fact that they can be remotely controlled through a separate signal cable. In general terms, a light needing two cables (one power, one control information) is intelligent.
Although this guide is for moving head lights, almost all characteristics are shared with scanners.For more information on the difference between moving heads and scanners, see our lighting guide.
Intelligent lights
Martin Mac 500, Mac 2000, Scanner
Generic lights
PC, Flood, Par can
What's the advantages of using a Moving Head Light?
They're pretty much the most versatile and powerful pieces of lighting equipment available. The ability to point your lights at any point on your stage, from the comfort of your lighting desk, is extremely useful and when combined with colour changing, multiple gobos, prism effects and beam shaping, you're pretty much limited by your imagination. They may be dynamic lights but once set up, they can be left to 'do their thing' for a while whilst you take a well earned rest.
Are there different types of moving head?
Yes, just like conventional lights, moving heads are available in Profile and Fresnel types. They share similar characteristics with their generic counterparts but are usually much more expensive and verstile.
Martin Mac 500 profile light
Martin Mac 600 fresnel light
What's the disadvantages?
Cost: Although the cost has plumetted in the past few years, a single Mac will still cost £2k-3k.
Speed: Moving a heavy light through 360° is technically difficult and requires good design and large motors. Consequently, the speed of movement is not very fast; for lightning quick pans and tilts, a scanner is the only real option.
Set-up: Although they are fairly easy to set up, it does take longer than a conventional light (rigging heavy light, setting DMX address, patching on desk). But then again, how many conventional lights can be replaced by a single moving head?
Features
Lets run through the features of the industry standard lights, the Martin Mac 500 and Mac 600:
Power (Mac 500: 750W Input)
Using one or two shouldn't be too difficult, but lots of lights will need a careful examination of the power supply. Although on paper, it looks weak, the light output is vastly greater then conventional lights.
Discharge lamp beam (mouse over for example of generic beam)
Discharge lamp light source (Mac 500: 575W)
These bulbs use electrons fired between two metal bars. These electrons energise the gas in between and this produces a vast amount of light which is spread across the visual spectrum and so appears white. Most generic lights which use filament bulbs which produce a yellowy light that is not as bright as a discharge lamp.
Shutter and disc dimmers
Dimming
Because a discharge lamp can only operate at fully on or fully off, an alternate way of decreasing the light output is needed. The light is kept permanently on whilst the light beam is blocked mechanically.
Mechanical Shutter (Mac 500)
One or two shutters are brought across the beam to block the top and bottom of it. Because of the location of these shutters in the light, the top and bottom of the beam is not cut off. Instead, the beam dims due to less light being able to exit the main lens.
Disc (Mac 600)
A disc with a varying amount of clear and black areas is rotated in front of the light beam. To dim from 100-0%, the disc rotates from its completely clear section to the completely black section.
A Mac's pan and tilt range
Movement
Motors in the base and arms enable 440° panning and 306° tilt. Moving heads don't move particularly fast however, for moving a beam of light at full speed, a scanner is far superior.
Strobe
Unlike conventional strobes which turn a bulb on and off at high speed, moving heads use a shutter moving across the light beam to cut out the light.
Most conventional lights (eg. parcans) take a finite time for the bulb to start and stop glowing when the voltage across it is cut. This means that the effect is less of a strobe and more of a quick fade. Moving head lights don't suffer from this problem, being able to go from 100% to 0% almost instantaneously. Conversely, a conventional strobe light can operate at a much higher rate than a moving head because it uses pulses of voltage which are much faster than a moving shutter.
Mixing wheels combining to give full range of colour
Colour
Besides movement, the main advantage of using intelligent lights come from the fact that the colour can be changed at will and to a wide variation of colours. Like Dimming, there are two methods used:
Filters (Mac 500, Mac 600)
These operate like gels and are rotated in front of the light beam. They can therefore only be of fixed colours but can be used to produce split effects where the edges of two filters split the beam, producing a very useful effect.
Colour mixing discs (Mac 600)
This works in the same way as the dimming disks except that the black areas are replaced by coloured filter. By having three of these disks (yellow, blue and red), the light can produce any colour you want.
Gobo effect
Gobos Most moving heads come with a range of standard gobos already inside but you can add your own if needed. (Backstage has some of its logo in size T [27.8mm dia.] to put inside Mac 500s). The effect is just like that produced by conventional profiles but with the advantage that the light can change its own gobos. The Mac 500 uses two sets of gobos, one static and the other which can be rotated. They can be used together to produce some interesting effects.
Prism
Not done in any generic, this effect splits the beam into 3 (or 5) images. This is best applied to gobo images and the prism can also be rotated, rotating the 3 images. The penalty for this feature is that each image is reduced in intensity by a third and care has to be used if a gobo, colour filter and prism are wanted together in a lit room.
Beam Shaping
By applying a directional lens to the beam, the spot can be changed into an oval which can then be rotated to the desired angle. It is particularly useful for illuminating people and objects which are wider or taller than normal.
Weight
Heavier than generic lights, most moving head lights usually needs 2/3 people to rig safely. The head will rotate and swing about freely when it has no power: be careful when carrying and rigging.
Use of Moving heads with lighting desks
Each parameter is controlled via a DMX512 control cable (3-pin in the case of Macs) and is provided with data on a number of channels in the same way every other DMX controlled device is. The light then uses different DMX channels for different parameters and varies this operation depending on the signal value. Instead of changing from 0-100% brightness, most of the parameters vary a number of things (eg. For DMX address 9, value of 0 has iris fully open, value 100 has iris half open, value 200-215 has iris fully closed, value 245 has iris randomly pulsing its size (opening fast), value 255 has iris randomly pulsing its size (closing slow).
Moving lights are incredibly versatile because of the large number of DMX channels used. Each can control separate aspects of the light and so you really need a lighting desk that can handle the vast number of channels without overloading the operator.
A bad way of operating intelligent lights:
A small, DMX-capable desk designed to handle a few conventional lights via a dimmer. By using the separate faders, the desk can be used to instruct the intelligent lights but the operator would have to be very accurate with fader control (eg. A 7% change in level will result in changing gobo and most effects are even more sensitive). The whole process would be very slow, difficult to control and each attribute of each light would have to be altered seperately.
A good way of operating intelligent lights:
A larger, programmable desk, designed to operate intelligent lights. Such desks usually have wheels or rollers to control the level of different attributes. The attributes can be selected by the press of a button, multiple lights can be used and the desk can produce its own multi-light effects.
Backstage
Technical Services,
University of Bath Students' Union, Claverton Down,
BATH, BA2 7AY Generously supported by the University of Bath Alumni Fund.
