REPORT 039
energy as photons (light) the colour of which is determined by the composition of the semiconducting material used. The prime difference between the two sources being that the process of electroluminescence requires much less electrical energy to produce light than the process of incandescence resulting in a more efficient and robust light source (LED has stated life cycles of up to 100,000hrs to 70% output). This process also results in a couple of major pitfalls, the most notable of these for our industry are the drawbacks in the colour rendering capability and the dimming curve of an LED source. Additionally, the critical issue with all LEDs is the quality of the manufacturing process which determines not only the light output and life but also dictates the ability to accurately reproduce the same colour from different cells, a quality that we have taken for granted when using tungsten fixtures and a one that has shaped our design techniques.
These pitfalls exist because we are in the infantile stages of development and are mentioned here not as a source for doom and gloom but as a means of pointing out that we are in an exciting crossover point for our industry. Just as the gas fixtures were retrofitted to incandescent in the 20th Century, the incandescent fixtures are now being retrofitted to LED source and the way we adapt to the advantages and disadvantages of this technology will define the way we design with these fixtures. The major design parameters most modern LDs take into consideration when selecting an LED source are colour rendering, dimming curve, output / perceived brightness, efficiency, life cycle and cost. Using these parameters as a guide we can make an informed choice as to which source, LED or tungsten to select for which application. Today, we have to take more responsibility for our fixture selection because the differences between two LED fixtures can be much greater than the difference between tungsten sources and using these parameters as a guide we can make an informed choice as to which LED use.
It is interesting to examine the way the industry is approaching this crossover period by looking to the fixture manufacturers and how they are incorporating LED into their product range. For example, ETC, with its Source four fixture, is one of the most successful tungsten fixture manufacturers but it is also paving the way with
new LED technology with its x7 colour system LED fixtures. It is positioning these technologies to work alongside each other, and create a hybrid lighting rig. For example, if you need high output white light then the best fixture to choose is still a tungsten fixture as the white LED fixtures still do not have high enough output levels. However, if you are after colour, the most efficient fixture to choose is a coloured LED array because you can create the colour you need at the press of a button. This hybrid approach seems to be the way that most LDs are approaching design with LED also, there is no perfect LED fixture so care must be taken to incorporate the correct fixture for the application.
In our work in Australia, we have come up against these issues on many major projects, the most notable being on a recent small theatre installation. The client brief was an all LED lighting solution doing away with tungsten completely. They came up against a number of roadblocks along the way. Firstly, they had to find a fixture with the right output level, colour rendering, and dimming. They eventually selected the ETC Source Four LED after an exhaustive test process. They then had to look at how they would incorporate touring productions and retrofitting existing tungsten designs, the solution was to incorporate tungsten LED fixtures. This was a compromise as the fixtures didn’t fully meet all the criteria when it came to colour rendering and interaction with filters. After all of this testing and design, the ultimate deciding factor became cost, the LED solution even with its efficiency savings was just too high for an initial outlay. Eventually, the solution was to produce a mixed rig of tungsten for white light and LED for colour. This scenario is common in our modern practice and illustrates the process of design that must go into choosing the right fixture for the right application.
Just like those stagehands of the early 20th Century, we the 21st Century lighting practitioners are the leaders of a technology revolution. The way we design with and work with the LED will inform the way the technology develops. We will see the LED evolve from being just an effect light or a wash light to become the mainstream light source of our industry, just as tungsten has been for the last 100 years.
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