Lighting with LEDs

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What are LEDs?

An L.E.D. is an electronic component (full name Light Emitting Diode) which produces light when electric current passes through it in one direction.
In recent years, the efficiency of LEDs has risen and the cost has dropped, meaning that it’s possible to use LED lighting in an entire rig without losing significant brightness.

What kind of fixtures are available with LEDs?

There are a wide range of types of LED fixture now available, which are beginning to mirror the qualities of incandescent stage lights.

elumen8tri8pixelbattenFlood

LED floods are usually single colour, but available with colour mixing, in various different sizes for applications as varied as outdoor security lighting through to specialised lighting for stage cycloramas.

Right: eLumen8 Tri pixel batten

ledjrgbparPAR

These are the most common, as they produce a wash of light similar to that from a Parcan or a Fresnel.
Usually RGB, but sometimes RGBW or RGBAW (red, green, blue, amber, white) for the best range of colours.
The beam size (like a Parcan) is not adjustable on most, although there are zoom versions available.

Left: LEDJ RGB Par

Profile

Only available in the last couple of years, companies such as ETC are leading the way in LED technology which beats the equivalent incandescent fitting, but with full, subtle, theatre-appropriate colour mixing. Although the products are expensive, again, the prices are dropping, and becoming more affordable. Most specialist suppliers will be able to demonstrate the products before you buy – it’s important to see what you’re getting, as the quality varies considerably if you choose cheaper products.

How do you use LEDs in a stage lighting rig?

LED fixtures designed for entertainment use are not the same as regular stage lights. They must not be connected to a dimmer. The electronics that run and control the LED fitting are built into it, and require a constant undimmed power source.
A control signal must also be connected to each LED fixture, which comes direct from the lighting desk, and is known as DMX512.
Some LED fittings are single colour, but most contain LEDs which can produce Red, Green and Blue light independently. These LED fixtures are known as RGB, and enable a wide range of colours to be produced on stage by mixing them together in varying amounts. An RGB fixture requires 3 DMX512 channels to control it, one channel for each colour.
An even wider range of colours can be produced using RGBAW LED fixtures (Red, Green, Blue, Amber, White), including more subtle pastel shades. These require 5 DMX512 channels.
Each LED fixture has an ‘address’ which can be set on the fixture, and tells each unit what control channels from the lighting desk to respond to.
For example, in a small drama studio with 24 dimmers, the control desk needs 24 channels to control them. Adding LED fixtures into the studio increases the number of control channels required. Adding four RGB LED fixtures will add 4 x 3 = 12 channels, if they’re all to be controlled separately. So, in this example, the channels are allocated as follows:

Control Channel Function
1 through to 24 Dimmers 1 to 24
25 LED #1 – Red
26 LED #1 – Green
27 LED #1 – Blue
28 LED #2 – Red
29 LED #2 – Green
30 LED #2 – Blue
and so on  

In this case, LED #1 would be set to start address 25 and LED #2 would be addressed to 28.

If you want all of the LEDs in the rig to respond in the same colour at the same time, you can set them all to the same start address (e.g. channel 25).

The lighting desk channels can then be mixed to produce the required colours.
Modern computerised lighting desks make life easier by enabling you to control all of the colours by only selecting the LED fixture once. MORE INFORMATION COMING SOON.

Why use LEDs? They cost a lot more than regular instruments.

LEDs are far more energy efficient. An LED flood may use only 30 Watts of power, but produce the same amount of light as a 300 Watt traditional floodlight. As the industry becomes more aware of the need to use sustainable practices, LEDs are becoming essential.
LEDs enable an (almost) infinite variety of colours to be produced on stage without having to rig lots of traditional filament lanterns with gel in front of them. This is a vast saving in time and effort. The colours can be adjusted without climbing a ladder.

What is the difference between the cheap ones and the really expensive ones?

  • Flicker
    Incandescent (filament) light bulbs have a relatively slow heat up / cool down time. The light fades (over a fraction of a second) when you cut the power. However, with an LED, the light cuts off completely and instantly as soon as the power is removed.
    LED lights at 100% do not flicker noticeably, but as they are dimmed electronically, the flicker is visible to a video camera (if not to the naked eye). If an LED colour (in a cheaper fitting) is kept at a low level, the flicker will be very noticeable on video recordings.
    The higher the refresh rate of the LED, the faster (and less visible) the flicker.  The flicker rate is measured in Hertz (Hz) – cycles per second. So, a 400Hz refresh rate means the LEDs flicker 400 times per second.
    COMING SOON – Video demonstration of LED Parcans with 400Hz refresh rate.
    More expensive LED units have very high refresh rates which do not show up on video, regardless of the intensity.
  • Smooth Dimming
    As the LED gets dimmer and dimmer, there comes a point when it just cuts out (switches off). With cheaper fittings, this cut off is more pronounced and more visible.
    COMING SOON – Video demonstration of LED dimming.
  • Brightness
  • Colour Rendering
  • Reliability
    As the cost comes down, the chance of the electronic components (particularly the power supply) in the unit rises. You get what you pay for – if you buy a cheap product, assume it will not last very long.

Why does everyone not use them all the time?

  • Cost
    An LED instrument costs a lot more than one using standard filament bulbs.
  • Colour Rendering
    LED light can appear cold and harsh – it lacks the warmth and subtlety of tungsten lamps.
  • Controllability
    Although the LED fitting is connected to a control signal from the lighting desk, the electronics in many cheaper LED fittings do not allow them to dim completely smoothly, resulting in a ‘stepped’ dim, rather than a smooth seamless dim.
  • Noise
    Some LED units have fans to keep the electronics cool, and these add to the ‘noise floor’ of a studio theatre space.

MORE INFORMATION AND ILLUSTRATIONS COMING SOON