Rob is a Lighting Designer and Lighting Programmer and currently Senior Lecturer in Technical Theatre Production. He is also the Editor of On Stage Lighting and teaches stage lighting practice.
While looking at the new ilumo ZOOM LED Spot, On Stage Lighting considers the future of colour in stage lighting control and revisits an old problem with a possible solution that leads to further questions.
The Colour Mixing Problem
In a past article, we looked at a specific problem concerning the crossfading of colour mixing lighting units and the possible visual hideousness that can be the stopping off point between one colour and another.
Briefly, the principle of channel value controlled colour mixing and state based lighting create an problem. When channel levels create a mixed light colour based on the intensity of individual colours like Red, Green and Blue (RGB) sources, a fade between these colours sends the values through a series of colours including what might be termed Dull White.
Colour Mixing and Crossfades suggests ways in which these transitions can be managed, either by hand or using additional cues as stopping off points that create an A-road bypass around the Dull White and avoid unwanted colours between two lighting looks.
The Colour Control Problem
The way we currently run colour mixing fixtures using additive RGB, RGBW et al and subtractive CMY uses control channels for each colour component intensity. This used to simply translate to a series of 8-bit values on an encoder (or even earlier, a fader) but lighting console makers wanted to give us more. They created ways in which we could “pick” the colour or align it to a simplified colour model that might approximate, say, a Lee filter. By somewhat crudely mashing up a series of values, a colour was produced that didn’t involve wheely-wheelying each individual colour emitter to it’s desired intensity.
But “crudely” is the key. The actual resulting colour output is, of course, very much based on the light source it is being used with, what colour temperature discharge lamp, the colour of the Magenta flag or which “Red” LED. This mashing of values and the variable nature of the light source depending on fixture type, has always led me to create my colours while avoiding things like “colour pickers” and any adjustments made are directly controlled by said wheely-wheelying the specific colour channel.
Some professional consoles give the programmer the option to use Hue, Saturation and Intensity (HSI) or some similar model to set the exact colours. These systems don’t really address the issue that a lighting console doesn’t actually see the colours it thinks it’s outputting and can’t really judge if the Cheapo-LED Pro is actually the same steel blue as the Lari*lite 2000 Wash.
The CIE Colour Space
Before we go anywhere, you should probably know about the CIE colour space. It’s extremely interesting and science-y if you are extremely interested in science-y things. If not, it’s basically a mathematical way of describing a particular colour, based on coordinates and can be visualised with a lovely rainbow thing shaped like, well, something. The important bit is that, using these coordinates we can describe colour. Handy.
The ilumo Zoom LED Spot
I recently took a look at the ilumo ZOOM LED Spot, following it’s formal outing at the Frankfurt show. The last time I saw the prototype, it was more of a non-working model, but this time Lumonic’s baby was full of life and I had plenty of questions for the designer of the ZOOM Spot.
Well, ok, so it’s not really a spot. If you expect it act like a projector or profile spot, it doesn’t.
The Zoom LED from Lumonic is a fixed PAR style colour mixing fixture, with a remote motorised zoom. It’s based on OSRAM high brightness LEDs in an array and goes from pretty darn tight to nice ‘n’ wide. The ilumo is DMX controllable, has all the things you’d expect from a professional level colour mixing PAR-like and a load of other things too. We’ll let you head over to the website to mug up on all these things, but notice that the design pedigree of this fixture is not insignificant, having a heritage with the orginal JTE Pixel range of LED kit including the famous “1044”. If you know your MAX2s from your RGB DMX modes, hold that thought.
There is much to talk about in this LED fixture, but this article isn’t a product review. We are more concerned with the concepts for colour mixing control , of which the Zoom Spot flags up.
The ilumo ships with range of possibilities regarding the way the unit is controlled via DMX (or similar: Artnet, sACN etc.) and these possibilities are wrangled into what they call “personalities” but you might consider simlar to fixture “modes”. These have been put together by the designers to give the user a single point of access to a specific setup, a bit like a stored series of settings, rather than what we think of as modes, which seem to be most manufacturers way of making sure you end with a fixture that will Pan and Tilt, but won’t open it’s dimming shutter!!
Within this personality, one channel of DMX control may be given over to what the ilumo call “Colour Control”, which in reality sets up the unit to behave in certain ways regarding it’s use of colour. Remember, this is controlled remotely from the console using ranges on a single 8-bit channel, effectively giving you control over the colour model at any given time, right there in your cues. In P6 (Personality 6) the channel map looks like:
- 0-40 RGBW (raw)
- 41-80 RGB (calibrated)
- 81-120 CIE x & y
- 121 – 160 CIE Colour Temperatures 2000K to 10000K
- 161-200 Palette Selection
- 201-255 HSI (& Colour Temperature)
The first part of this channel range simple sets the fixture to a standard RGBW model, in which a Red at full equals all the Red emitters are full pelt. But take a moment to look at the other models, all interesting in their own right. HSI is there and is what is says on the tin, plus something called calibrated. There is mention of the CIE coordinates x and y, but more on that in a moment.
With all the mention of colour temperatures and the problems outlined at the start of this article regarding the somewhat vague nature of colour mixing, it’s worth looking at how calibration works within the ilumo. For a start, what you are looking at is the fixture itself designating what colour it is, based on things such as your chosen CT or calibrated Red, Green and Blue sources.
What this means is that you can set the Red at the fixture to be “LEE 106” or “LEE 027” and other possibilities, customisable or standard. Obviously, the LED units themselves don’t swap out for new ones, the fixture creates the base colours with a combination of it’s given raw material and an uplift in this calibrated “Red” might involve a change in all RGBW LEDs. You can see why this is called a Colour Engine already. We are pretending to control this RGB fixture in a simplistic way, and it’s busy doing stuff under the hood.
CIE X and Y Coordinates
As we now know, you can pick a colour using the CIE colour space using numbers, and this is where the CIE x & y comes in. Again, we are now looking at taking out the vagaries of the console colour picker and identifying exactly a colour that the engine will attempt to reproduce. I have to say at this point, that these in-fixture calcs presumably don’t take into account the age of the LEDs themselves or the batch, possibly not even the model generation of the ilumo range. Anyone that has worked with a large quantity of JTE 1044 Pixelline of different ages, from different hire companies, will know the shenanigans involved in putting all that “that sort” next to “those other ones” when it came to getting and even colour. Now, of course, LED technology has advanced and perhaps such variance is less common.
But keep the CIE model in your mind as we move on to…
In lighting programming, we know what “palettes” are with regard to consoles. They are a preset thing, including colour, that we can save away for later use and update centrally. They are the centre of our world. The ilumo uses the term “palette” accurately, but not in the way we moving light programmers think of it. So let’s call them “Stored Colours” for the minute.
These stored colours are recalled by one of two DMX controlled channels, I didn’t get if they stored the same colours or different ones on each channel, to be honest. The key thing is that the two channels act like an A/B buss, like a DJ mixer. One channel sets up one colour, the other, another a second colour. The final piece of this puzzle is the third X-Fade channel – it’s the sideways slider-y thing that DJs like to fiddle with. It fades between the two colours, loaded up on the A and B busses.
“But why?” I hear you ask. “Surely, we don’t need to set up a colour on a channel and another on another channel, and upload and store it in the LED fixture to then crossfade between them. I spent good money on a lighting console that does that for me and without so much faffing about!!” Well, it’s a good point.
The interesting thing about the ilumo ZOOM Spot is the reason it bothers with all this in the first place. The colour engine goes out of it’s way, to, well, go out of it’s way!
What I mean is, the crossfade from colour A to colour B deliberately doesn’t take the path that leads through Dull White or other colour nasties. The fixture finds a route from one side of the CIE colour space to the other, while trying to avoid Yuckville around the middle.
I’m not entirely clear how the routing decisions are taken but tested it out and it does actually work, presumably the engine interpolates between the two colours, rather than simple changing intensities in a linear fashion. The acid test for an RGB fixture is something like a Red to Cyan crossfade, taking the LEDs at their extremes and crossing them over. The colour route wasn’t half bad and there was no discernible dips or bulges in intensity during the transition.
All these interesting solutions and options for more accurate colour control create some interesting questions, which probably don’t have one answer for everyone:
Are colour mixing fixtures expected to make a better job of their colour business within the fixtures themselves, making it easier on the end user and the lighting console?
Is it better that the dumb kit just takes instruction from a calculating console, which in turn needs a lot more information about the light source than it currently has? (Cue minor rant about the nature of console fixture personalities)
Is the additional effort of creating and storing colours in a fixture, in order to make use of it’s colour cross fading engine, offset by the benefits to the lighting designer of better transitions?
Can I ever think in CIE coordinates? And if I do start with a CIE colour, can I edit in them or do I need to return “bumping up the Green a bit”? I don’t mean “Can the kit do this?”, can my brain?
Are we happy to simply create console colour palettes up for various fixture types, adjusting them and matching them by eye, and putting up with dealing with transition issues using the various workarounds we have at the moment?
How does a fixture with such proprietary colour control fit onto the consoles of today and tomorrow, with their current colour setting arrangements? If other colour mixing kit doesn’t use such a control system, does it even matter?
Are we finally seeing the limits of DMX and other dumb channel based one-way control for complex fixtures? And are workarounds like the A/B Colour buss just pandering to an old system when we should just get up to speed with our controls?
The ilumo ZOOM LED Spot is a very interesting piece of technology and control implementation, as well as being a very nice piece of kit from the lighting designer’s point of view. Lumonic says their mission is to “challenge the status quo” and there are elements within their patent pending Colour Crossfade Engine that certainly does that. It also asks questions of us as programmers and those that design our interfaces.
Appendix for DMX chart nerdery – Personality P6 channel mapping:
- Red (or Red calibrated or Hue)
- Green (or Green calibrated or Saturation)
- Blue (or Blue calibrated or Intensity)
- White (or White CT)
- Dimmer Speed
- Master Intensity
- Colour Control (mentioned above)
- Colour Temperature
- CIE x coordinate
- CIE y coordinate
- Palette A (colour buss discussed above)
- Palette B
- Palette Crossfade (A/B)
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