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Dedo Weigert reveals cinema led lights future
First Publication: by Nathanail -altcine team- 20.10.2011
 
 
   
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Altcine converses with Mr. Dedo Weigert*, one of the great pioneers of cinema lighting industry, concerning the “new” LED lighting technology and its use in cinema...
A technology which he began to tame for quite sometime now.

Dedo Weigert is the inventor of the renowned Dedolight, multi awarded for his patents and inventions and we are pleased to inaugurate our technical articles section with this greatly informative interview.

Even if “these questions cannot be answered in short” - as Mr. Weigert claims - because they open up a wide field of technological explanations to be made, we present you with this first version of our interview with “shorter” answers, and a promise to return with a comprehensive article on LED lighting in general.

altcine: Which are the benefits of using LED technology in modern lighting units?

Dedo Weigert: There are 3 attributes people usually relate to LEDs as a light source.

a)  longevity
b)  no heat
c)  lots of light

In some countries people think that using LED technology is a very good way to save the Planet, thus it could be very important. Today, in some aspects this may be true.

LEDs can be quite useful in street lighting, LEDs can be very good in automotive applications, LEDs can be nice and colorful when lighting architecture, bridges, river fronts etc.

In professional application for film, broadcast and photography, as well as for lighting in museums many of the white phosphor LEDs still have some serious disadvantages.

Most white phosphor LEDs still have very bad color rendition. In professional life we start with the sunlight which is attributed with a color rendition index (CRI) of 100.
Next come halogen lights which are given with a CRI of 98 and a full and very even spectrum, but the high voltage halogen lamps have a low output of 20 lumen per Watt.

The low voltage halogen lamps we use in the dedolights have a much higher light output, namely 40 lumen per Watt and also a perfect color rendition of 98. Having a very small light source in the lamps that we use, it is perfect for integration into optical systems which is our specialty. Many of the white phosphor LEDs have a CRI of 74. This is a quality of color rendition that no serious butcher would use to light his meat, because he wants people to find his meat attractive and buy it – but lighting it with such bad color makes it look terrible. All that professionals do every day is to light skin. The skin tone rendition of humans is very critical and with such bad color rendition the only way that allows us to think of such light sources is the magic button of white balance on the video cameras, this making it halfways acceptable, as long as it is not mixed with any clean light sources. Mixing it with clean light sources could cause different color rendition in the same image which cannot be fixed in post-production, although ‘we will fix it in post’ seems to be one of the most misused phrases in our business.

There are very serious developments in LED technology, and every few months new LEDs appear on the market. We work together with four highly competent manufacturers of LED light sources, and together we try to improve the color rendition. We have already made several very serious steps and by now we are able to offer LEDs that have a much more acceptable color rendition. The hopes are that in the near future there may be LEDs which give a much fuller spectrum, much better color rendition.
We have learnt that the color rendition index on its own as we have used it for many years is not sufficient anymore to qualify the color rendition quality. Now we have to look at R1, R2, R3, and so on, all the way through R14 which is the color rendition of individual colors, and then we find that usually R9, which is the color rendition of full red, is very bad with most white phosphor LEDs.
Similarly, many of the fluorescent light sources generally have a low CRI and are lacking in the R9 values.

Multi-color LEDs can be used similarly to the 4 chamber lights that have always been used in broadcast and theater, with red, green, blue, and white light sources from which you can mix pretty much any color.
To some extent this is true with LEDs, except that here we mix red, green, blue, white and amber. If we add this fifth color we can devise a control system to mix the intensities well and we can already achieve a pretty good color rendition with LED lighting systems. Sometimes, however, it is very difficult to use such mixed color LED arrays in lights with optical systems. For panel lights, where many LEDs are arranged in the same plane, such systems can already be quite successful.

Light Output
When people want to save the Planet they think that this is most energy-efficient light source on Earth. At the moment this is not really true because the standard white phosphor LEDs give a light output of 60 lumen per Watt which is still considerably lower than the light output of a fluorescent tube with 80 lumen per Watt or an HMI type lamp (metal halogen lamp). Such discharge lamps also give 80 lumen per Watt. In other words their light efficiency supersedes that of LEDs.

The third big myth is that LEDs are supposed to give no heat. That’s an absolute lie. One of the biggest problems of LEDs is heat. Admittedly the forward heat is relatively low, but the heat that is generated on the LED and behind the LED is considerable so that enormous cooling surfaces are needed to keep a proper working temperature for the LED. If sufficient cooling is not applied, the light efficiency goes down drastically, and the color stability goes even further down than it already is, rendering such systems less useful.




As with the longevity of LEDs they are attributed a lifetime of 30.000 to 50.000 hours. However, it has to be considered that the LEDs which can be bought today change very quickly. The efforts to improve LED technology are absolutely intense, similar or even more intense than in the development of new generations of computers. If you buy a laptop today you know already that in 3 months it will not be the latest generation anymore. Today, many of the LED systems for professional use will be outdated before they have shown their lifetime efficiency.
Future LEDs will have better color, will have higher light output, and may possibly generate less heat. This means, whatever we see today may be outdated relatively soon.
Many LED systems which were built for professional use are not used anymore because the light output efficiency of the early white phosphor LEDs went down after only 500 hours. Some people even say that they went down to less than 50% of their original efficiency. This has been improved by now and when switching on an LED, the efficiency may go down by 10%, again depending on the heat. What happens over the long lifetime which is stated in some specs is not fully known today. All these are more or less estimations.

altcine: Why has Dedolight turned to that technology, given the fact that it already was a company with excellent record in cinema lighting gear manufacture?

D.W.: Dedolight has not turned to LEDs. We are using all kinds of light sources, and we have always looked at all kinds of light sources by using very different ones.
We have used high voltage halogen lamps, low voltage halogen lamps, and metal halide discharge lamps. In cooperation with one lamp manufacturer we have developed an absolutely novel metal halogen discharge lamp which gives pure tungsten color temperature. Thus, some of our lighting instruments have interchangeable light sources where one can switch from daylight to tungsten by mere lamp change, using the same ballast. This gives us very clean color rendition and a high light efficiency of 80 lumen per Watt for the light source.
Here we have to differentiate between the efficiency of the light source and the lighting instrument. I may remind you that a typical Fresnel studio light in the spot position simply has an efficiency of 6%. Think about it. If it incorporates a halogen lamp then 90% of the energy used turns into heat. Only 10% turn into visible light, and from those you effectively use 6%, which turns out to be 0.6% of the energy. Doesn’t look very exciting when you want to save the Planet.
The dedolight optical system by virtue of its optics already gives us 18% in the spot position which is not a miracle but at least we are 3 times better.

Furthermore we have some ceramic lamps which usually have been quite critical for color rendition. Again, with one lamp manufacturer we were able to establish ceramic lamps with a very high CRI.

We have always looked and will always look at every possible light source, experiment with and evaluate it. We have highly qualified technicians who do nothing but measurements of such light sources. After the stages of computer design of the light fixtures we again evaluate their efficiency for color distribution, light distribution, color quality and light efficiency.
We haven’t turned away from what one may think is ‘old’ technology – we have always been leading in optical design. We were the first ones to change the principle of the studio Fresnel light which is still being built without any alterations for the last 100 years. We were the first ones to include an optical system with 2 non-spherical lenses. As you may well know the typical Fresnel lens is a spherical lens which cannot equal our systems in light distribution and color distribution.

altcine: Do you believe that in the near future LED lights will be the ‘new standard’ in cinema lighting equipment?

D.W.: LED is not LED. This is not one big pot of Goulash that is all the same. We have to differentiate very seriously.

There are light sources where many LEDs are arranged in one plane, the so-called panel lights. Those are widely used, and we also have many of such versions, getting better and better with higher light efficiency, better color rendition. However, if one wants controllable light (you mentioned the word ‘creative’), we must realize that such light panels are very hard to control. It is very difficult, and there is no elegant method for such multi-LED panel lights to finely-tune their focusing. You cannot use barndoors without winding up with very ugly multi-shadows, in other words the control of the lighting which is one of our main goals and issues is very hard to realize with such LED panel lights. For these reasons we build LED systems which we can integrate into our optical concepts and we have already built several focusing LED lights with a pretty good focusing range, good light distribution, even color distribution, and reasonably good color rendition.
At IBC we have just introduced 2 new generations of such lights.

altcine: What is the most important step in LED lights construction (technically speaking)? Choosing the right LED units, circuit design or quality control?

D.W.: If I was to give you a good answer to this one it would take many pages and it could only reflect today’s technology, well knowing that the technology is going to develop extremely fast. Again, you have to differentiate. The technology of the LED light source and the technology of building the lighting fixture, the optical system, the reflector design, the lens system, and all the control devices that belong to creative use of lights in cinema, broadcast, photography, and in high-class museum lighting.

altcine: What do you think is the next step in LED lighting technology advance? Will we see large outdoor units like HMIs in Fresnel shells?

D.W.: Again, what will be the next steps in LED technology as far as the light sources are concerned.
Here you will read about remote phosphor technology which seems to have some distinct advantages. You will read about OLED technology which has not really arrived.
You will read about plasma light sources which do exist, but in my mind still have severe draw-backs. There are some plasma light sources which are already used in moving lights, and I was introduced to a very interesting sulphur light source at the Lomonossov University in Moscow claiming extremely high light efficiency and a clean continuous spectrum like the sunlight. But then it seems to turn out that this technology still is not fully developed. Such systems don’t seem to dim very well, and they are a bit cumbersome since they need something like a microwave oven around the light source to make it function. For this the cost and the technology are still cumbersome and expensive. What I have seen did not have any clean spectrum, nor the ability to control the spectrum effectively. So for some time to come people will build larger and more powerful LED panels, and eventually, as the LEDs get better those will be able to give a pretty high light output, and if the cooling can be mastered, they may easily find their place as some large surface light sources. For now, looking directly at such light sources is very blinding, giving an aggressive feeling. Eventually those will be combined with large diffusors, but again for creative and artistic use I believe that our focusing LED lights are the only ones which come close to the control that is needed for truly creative work. Larger LED panels may not give such abilities for some time to come.

This is my short answer – it may have turned out a bit longer than you were expecting. However, this is by no means the complete answer, but just a first indication of what may be involved. Even if we were to look at everything we know today, we are perfectly aware that this technology is still undergoing many changes concerning good color rendition, high light output and the combination of both of those qualities.

altcine: Thank you very much Mr. Dedo Weigert.


*Dedo Weigert was born in Breslau, Germany in 1938 and studied at the Munich University. He went on to work extensively in theater and as a film production manager. For several years, he was an assistant cameraman on many international film productions and in 1964 started working as a freelance cameraman (Director of Photography).
With over twenty years of experience as a working director, producer and Director of Photography involved in feature films, commercials, documentaries, American television series and some highly technical and demanding special projects he began to specialize in high speed cinematography and high speed videography.
Mr. Weigert has received more than twenty international patents for technical inventions that are today regarded as state-of-the art. He has also been awarded twenty-five international prizes for film and technical development such as the Technical Achievement Award in 1990, Cinec Award in 2002, and the Scientific and Engineering Award in 2003. (from Dedo Weigert Film Site).

 
 
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  A Lighting Masterclass, by Dedo Weigert on Vimeo (2009)
  Dedo Light
  Dedo Weigert Film
 
 
 
 
 
 
       
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