Deconstructing SGMs G-4 & S-4

DECONSTRUCTING the G-4 & the S-4

Create a powerful, yet compact wash fixture with interchangeable lenses and an efficient LED lightsource that is based on additive mixing. It should feature high-class color rendering in a lightweight construction, while keeping the irreplaceable fresnel optics and external cut of the barndoors. That was the challenge SGM faced. On top of it, 3 conditions had to be met:

It must be IP65-rated (maintenance free and weatherproof for outdoors applications).
Two variants should be available: a moving head and a static fixture with motorized zoom.
No more than 200W and 10Kg.

I must admit, we went through a lot of pressure, but the guys in R&D had a lot of fun.

"When Jason Bruges Studio approached me to design the lighting for this city wide installation that was to be outdoors during the winter months, I knew we needed SGM onboard (...) The S-4 gave us a bright source in small form factor with beautiful colour correction and dimming," said Carlos Valente about the beautiful installation for the 2017 City of Culture

THE RULES OF THE GAME

If our G-4 and S-4 family sounds familiar to you, then you know for sure why it is so important for SGM to conquer high color rendering with minimal LEDs. Colors have a lot to do with powerful feelings, but also with image reproduction. The more powerful and stable our pure RGB color mixing is, the more impressive and colorful effects our users can achieve. Now, for those lighting designers and directors of photography who want to reproduce high quality visual scenes in a wide color temperature range, the spectral power distribution of our luminaires means a lot. By adding new colors to a RGB lightsource, it is possible to fill some of the gaps in the color spectrum of LED sources, while keeping the high output and deep saturates of additive color mixing.

But how many LEDs should we add to the RGB mix? The more LED color sources you need to achieve a brilliant color reproduction over the whole visible light spectrum, the more heat you generate inside the fixture. More LEDs also need more power. And these two factors usually end up in big and inefficient fixtures. The big questions were clear: Can we generate a high-quality white with only five colors? And, more importantly, can we achieve it in “raw” mode with no loss in output? The original idea was therefore to develop an LED lightsource based on Red, Green, Blue, Amber and Mint LEDs going through a hand-made glass fresnel lens that were able to reach high values in TLCI, CRI, CQS, and Rf color measurements when all chips were running at their best.

5 LEDs TO RULE THEM ALL

G-4 Wash

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After a long period of testing, the G-4 prototype matched our boldest predictions: a Television Lighting Consistency Index of 92.6; the EBU recommended measurement for LED fixtures. It is important to note that TLCI-2012 scores are more spread out than CRI values. In a TLCI index between 85 and 100, errors are so small that a colorist would not consider correcting them, while a CRI of 90 is widely regarded as the absolute minimum for television use. Fortunately, the G-4 and S-4 score a Color Rendering index of 92.1 when the LEDs perform at their maximum output.

Another commonly accepted way of measuring color reproduction is the Color Quality Scale, developed by the NIST to improve CRI Ra method. The CQS score of G-4 and S-4 in raw mode is 90.7, which is a very interesting value since this system is based in all types of color samples, including high saturates. Finally, the G-4 can achieve a very decent 87.4 Rf score. All these numbers appear in a 6,938K color temperature with 6,737 lumen output, which equals 117,387 cd at 15.5º beam angle.

BACK TO THE FUTURE: MOVING FRESNEL WITH MOTORIZED BARNDOORS

Designing an LED fixture is always a crossroad. Shall we go for new ideas only, or shall we keep the good ideas of the lighting industry? The G-4 is kind of a blast from the past, however, with a lot of brand new concepts. So, here’s the deal: let’s make a fresnel that can output 3,000 luxes at 5 meter distance in a 360º panoramic range, so we can have different sets lit with one single fixture, working from f/2 to f/4 at 100 ISO and 1/50 shutter in camera. And then let’s make it versatile: when working as a front light, we want a real fresnel, with the lighting cut after the lenses and a physical slot for a frost filter to enhance skin tones. Finally, let’s make it easy: no poles, wirelessly controlled, and no maintenance. Is that possible?

Yes it is. But no matter how good the G-4 Wash Motorized Barndoors works in a studio or theatrical environment, it should also look good in a music show, and it needs to be as powerful as a PC-like luminaire, if needed. Our choice was simple: 4 screws and a new lens: an affordable micro-fresnel optic for bright wash-beam aerial effects, or a single fresnel wash lens with a convenient top-hat.

G-4 Wash Motorized Barndoors

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MAY THE 4’S BE WITH YOUR CREW

Our big doubt was: Will the G-4 and S-4 series please the most demanding crews out there? We did our best to match their expectations, including standard features in SGM like linear color temperature control from 2,000K to 10,000K, a flexible color filter emulation (91 presets matching LEE catalog), and a wide motorized zoom range (from 9º beam angle to 76º field angle), while listening to the market. Diverse tools are needed for those master lighting professionals who deal with very complex cameras, silent environments, and powerful consoles. It is because of them and their valuable feedback that we developed the Studio Mode.

Our Studio Mode allows the G-4 and S-4 series to mix colors in 5 ways: the RGB + CTC mode for standard users, the more advanced RGBAM + CTC for those who want full control, HSI control for console lovers, mathematical XY coordinates over CIE1931 color space for purists of theatre, and the traditional subtractive CMY mixing used on white light sources. For accurate color adjustments, individual Plus / Minus Green control. Additionally, the fixtures include 16-bit dimming with incandescent curve for venues with a big setup of old tungsten fixtures, LED Frequency adjustment for high speed cameras, and, finally, for those who care about sound there is fan speed over DMX.

MODERN TIMES

Yes, these are good times: you can get the best techniques of all times, and the great improvements of today. And I am not saying the G-4 and S-4 series are the best lighting fixtures out there; I’m just saying that I love them. Maybe you see my point now.

S-4

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G-4 Wash-Beam

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Ben Diaz is Product Manager at SGM Light. He is responsible for the control and improvement of each of our luminaires during the entire product cycle - as well as directing the technical communication such as events, documentation, and shows.