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Autor: Dennis Jackstien


Lighting technology: Basics and characteristics (4 / 10) - Lighting technologies

An overview of the important designs and types.

Luminaires for film and television are fundamentally different from one another in two ways. Firstly, through the spotlight design (such as step lens, floodlights, etc.) - we'll deal with that in one of the following articles - and then through the lighting technology used. We want to take a closer look at and compare the lighting technologies that are currently being used.

The most important lighting technologies in Film & TV

A total of four different lighting technologies are currently being used on very frequent basis in Film and TV productions. These are:

  • Halogen tungsten light
  • HMI daylight
  • Fluorescent tubes
  • LED

We will briefly explain and compare these 4 technologies below. LED technology and HMI daylight will be examined in detail in later articles as they are very complex. For an initial overview, it is sufficient to compare the  key figures and properties of the 4 technologies and, in doing so, contrast the traditional lighting technologies with the respective modern LED technology.

Halogen tungsten

Halogen light is by far the oldest lighting technology which is still being used in large numbers for film and TV. The first light bulb was presented by James Bowman Lindsay in 1835, rather than Thomas Alva Edison, who didn't patent an improved version until 1879.

In the case of an tungsten lamp, a thin wire (e.g. tungsten filament) is made to glow by electric current. The wire gets very hot in the process, sometimes reaching 2,500 or 3,000 ° K, which also gives the names of the color temperatures. The wire would melt at well over 3,000 ° K. Therefore, tungsten lamps are always warm white and not available in cold white.



Figure 1: Halogen tungsten lamp OSRAM 500W GY9.5 [Illustration from manufacturer OSRAM]


Normal light bulbs work very inefficiently. 95% of the energy supplied is not converted into light, but only into heat. The efficiency is only 10-15 lumens / watt.

Difference between halogen light bulbs and normal light bulbs

Halogen filament lamps are used almost without exception in film and TV spotlights. A halogen is added to the glass bulb, which - to put it simply - captures vaporized tungsten again and brings it back to the filament (the so-called tungsten-halogen cycle). The efficiency can thus be increased to 25lm / W, the lifespan is extended and the lamps can be built significantly smaller.

Halogen lamps in power classes of 100 - 24,000 watts are used in typical film & TV spotlights and operated directly with 230V AC voltage. (An exception is made for small low-voltage lights, such as DEDOLIGHT with 100W - 12V or 150W - 24V, which are more efficient but require a transformer to operate.)

Both halogen and normal incandescent lamps generate an absolutely continuous light spectrum and thus have excellent color rendering (CRI> 99). Halogen incandescent light is therefore often used as a reference in color rendering tests.


Figure 2: Tungsten light spectrum [Illustration: Dennis Jackstien]


The advantages and disadvantages of halogen incandescent light compared to LED can be summarised as follows.

Advantages:

  • Excellent color rendering (CRI> 99)
  • Usually. no ballasts or electronics required for operation
  • Attractively priced

Disadvantages:

  • Very inefficient and great heat generation
  • Lifespan only about 500h (at 3,000 Kelvin)
  • Color temperature drops when dimming
  • Sensitive to shocks and bumps

Fluorescent tube

Tubular fluorescent lamps are also widely used in film and TV and mainly come from the manufacturer Kinoflo. These are low-pressure gas discharge tubes where the gas filling is illuminated by 2 electrodes. Due to their particular construction, fluorescent tubes are only suitable for area lights (softlights).


Figure 3: Kinoflo 4ft, double bank [Image from manufacturer KINOFLO]


UV light is generated inside the tube. The phosphor coating of the glass converts it into visible light. The market offers fluorescent lamps in all color temperatures and also, to some extent, in effect colors like red, green & blue. A correspondingly complex coating of the tubes makes it possible to achieve a high-quality light spectrum with good color rendering. However, efficiency suffers. Fluorescent lamps with CRI> 90 usually reach about 50lm / W, but some versions manage to reach more.


Figure 4: Spectrum fluorescent tube 5600K, CRI>90 [Image by Dennis Jackstien].


A ballast is always required for operation that limits the current flow and also offers a dimming function in modern versions.

LEDs are now superior to fluorescent tubes in many areas. Higher quality LEDs are now more efficient, more durable, better dimming control, adjustable in color and also in color rendering. Therefore, even with soft lights, fluorescent lamps are being increasingly replaced by LED technology.

The advantages and disadvantages of fluorescent tubes compared to LED can be summarised as follows.

Advantages:
  • Very good soft light source due to the construction
  • Allows quite light luminaire construction even with higher output

Disadvantages:

  • Less efficient than LED with good CRI (as of 2019)
  • Good lifespan of 10,000 hours (but still worse than LED)
  • The color temperature can only be changed by changing the tube
  • Ballast absolutely necessary

HMI daylight

HMI daylight is also a discharge technology. The pressure in the lamp bulb is, however, much higher than for fluorescent tubes and therefore one speaks of high pressure discharge lamps. The designation "HMI" is only a model designation for the type of lamp from the manufacturer OSRAM. Other manufacturers use different names for lamps with very similar properties (PHILIPS "MSR", GE "CSR", KOTO "DIS").
"HMI" has become a general term and we will use it here as well.


Figure 5: OSRAM HMI 4000W/SE [Image from manufacturer OSRAM].


HMIs work very efficiently with approx. 95lm / W and generate a daylight spectrum not unlike that for the sun. The spectral curve is a little more uneven than in the case of halogen, but all spectral components are present and, overall, HMI also achieve very good color rendering of CRI> 90.


Figure 6: HMI daylight spectrum [graphic by Dennis].


HMI lamps are available in power levels from under 100 watts up to 24,000 watts. Frequently used performance classes are, for example, 1.200W, 1.800W, 2.500W, 4.000W or 6.000W.
As with fluorescent tubes, a ballast is required to operate HMI lamps. Generally speaking, this is separate from the lamp, and both can either be rented or sold together as a set.


Figure 7: ARRI M40 with ballast [Image from manufacturer ARRI]


In general, HMI daylight systems require a start-up time of several minutes until they reach full brightness and a stable color. They can only be dimmed to a limited extent and, in some cases, are not hot restrikeable. This means that after switching them off, they may have to cool down for a few minutes before one can restrike.

In our comparison, HMI technology is the most powerful but also the most expensive technology. For example, an HMI set with 4,000 watts of power (ARRI M40 light + EB4000 ballast) now costs around € 15,000.
There are a few more things to consider when operating HMI systems (frequency settings, flickering, UV component, noise, dimmability, etc.), which we will discuss in more detail in a separate article on HMI technology.

The advantages and disadvantages are only briefly summarized here.

  • High efficiency in sun-like daylight color
  • Available in large power levels up to 24,000W
  • Small lamp design allows the construction of bright lens & reflector spotlights

Disadvantages:

  • Comparatively expensive technology
  • Ballast required
  • Start-up time of about 5 minutes
  • Dimmable only to a limited extent and,  n some cases, not hot restrikeable

LED

LED technology has made a triumphant advance in our industry ever since 2008 and now almost every conceivable kind of spotlight has LED technology. (An exception are high-performance HMI daylight systems because they still can't be adequately replaced with LEDs.) Completely new spotlight designs have now appeared that would not have been possible without LED technology. These range, for example, from flexible lighting systems through to light networks.


Figure 8: CARPETLIGHT with "sewn-in" LEDs [Image from manufacturer CARPETLIGHT].


LEDs are tiny, highly efficient (> 100lm / W are now also possible with CRI> 90) and can be used very flexibly. Unlike traditional lighting technologies, LEDs neither have glass bulbs nor filaments or the like. In simple terms, LEDs are simple semiconductors that generate light when a voltage is applied.

The spectrum of colored LEDs (such as red, green, blue) has a narrow-band and therefore does not produce good color rendering. However, by applying phosphor layers on blue LED chips, broadband, white light can be generated and this process has now been so perfected that CRI> 90 is easily possible with white LEDs.


Figure 9: Spectrum RGB LEDs mixed to "white" (CRI<50) [Graphic by Dennis Jackstien]


Figure 10: White LED spectrum with CRI>90 [graphic by Dennis Jackstien].


In general, color deviations in LEDs (keyword: binning) are still a problem. These and other issues (e.g. flicker, aging, temperature drift and much more) will be covered in a separate article on LED.
If LEDs are operated properly, they have a very long lifespan of 30,000 hours and above. As a rule, however, some electronics (PWM drivers, power supplies, potentiometers etc.) are used to operate the LEDs. 

The lifespan of an LED spotlight depends more on the high quality of these components. It is important that one cools the LEDs, e.g. with heat sink or fan, or else the lifespan of the LEDs will rapidly decrease. For this reason, powerful LED spotlights are usually cooled in a very complex manner and therefore also comparatively heavy. Lightweight LED lights which can be attached to the wall, for example, are only available in the lower performance classes.

Another advantage of LEDs is their dimmability without any color changes. By mixing different LED colors in one luminaire, systems with variable color temperature or effect colors can be created, including the simulation of campfires, police lights and much more.
As previously mentioned, LED technology is very versatile and complex and we will take a closer look at this in a future article.

The most important advantages and disadvantages of LED can be summarised as follows:
Advantages:

  • Very high efficiency of> 100lm / W with CRI> 90
  • Also ideal for battery systems
  • Dimmable and color-adjustable on many models
  • Extremely long lifespan
  • Tiny design makes it possible to have new flexible luminaire types

Disadvantages:

  • Color tolerances and not always good color rendering
  • Require cooling system, therefore complex and heavy with increasing performance
  • Elaborate electronics, also partly a problem with flickering
  • The lamp is usually not replacable if it has a defect

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