In Uncategorizedby tfwm

At LDI 2006, the hot topic was LED technology. We caught up with Lighting Designer Stephen Ellison to get his take on the emerging LED phenomenon.

TFWM: What are the main differences between an LED and a Standard fixture?

Stephen Ellison: It’s the light source. You have LED fixtures and you have conventional fixtures. Your standard light sources are your incandescent lamp, which is rarely used in theater anymore, and then you’ve got tungsten halogen, from there you jump into arc light. LED lamps are small and are used in groups to achieve output. The arc lamps are primarily used in the moving light sector of the industry.

TFWM: : Why specifically arc lamps for moving lights?

SE: The amount of output per watt, but you can’t dim them, so you have to have some sort of mechanical dimming for arc lamps. An arc lamp requires an electronic or magnetic ballast to maintain the arc, and so you have to have a mechanical dimmer. Therefore you don’t hook them up as a standard fixture which you could hook up to a dimmer. A regular filament type lamp you can hook up to a dimmer. They’re the workhorse of the industry right now.

TFWM: : Why do you need groups of LEDs?

SE: An LED is a low wattage light source, where I will put a single tungsten halogen lamp into a fixture; to match a PAR with an LED what you do is put whole bunches of LEDs together. Add 60 to 100 to 200 lamps that are LEDs in the fixture and they provide you the light source. You put them in an array. If you want colored light, you’re going to put in red blue and green LEDs.

There’s one manufacturer who favors seven different colors in an array. So you’re not going to have one section all red and one blue and one green, you’re going to have them all mixed in around each other, for color blending. The LED is really nice because they don’t use a lot of power, and they don’t produce a lot of heat. It’s all electronic, so the dimmer is a built-in device; so you eliminate the need for dimmer racks, and running huge amounts of power cables. They’re wattage draw is very low. You begin to look at things that have almost no draw, and they don’t need special dimming.

A fixture by Color Kinetics has 36 high intensity LEDs. It’s power consumption is 50 watts, as opposed to 575 watts. A 20 amp cable would handle say 2300 – 2400 watts. If I’ve got 50 watts per fixture, there’s easily 40 fixtures. So you can see the difference. If I had what used to be a standard PAR can rock n’ roll rig, we had 60 PAR cans on the front truss, and 60 on the back truss. That’s 120 times 1000 watts, which is 120,000 watts, divided by 120 volts, and we’re looking at 1000 amps worth of power. Typically we needed 400 amps 3-phase to power that rig. If I take 120 times 50, I’m at 6000 watts. Divide that by 120, it means I have 50 amps total. That’s three extension cords- and no dimmer rack. I can go around and put in three extension cords, no dimmers, and run DMX cables to them and I’m done!

TFWM: : Why do you not need a conventional dimmer to dim LEDs?

SE: It’s an all-electronic circuit. An LED is a semi-conductor. In order to control it, you have to tell it to turn on and off. You’re not doing it with a dimmer. There’s an electronic circuit card with LED mounted on the front and electronic components on the backside. The electronic components tell which LED to go on or off at which time. You’re going to have some form of microprocessor in the fixture that is going to translate the information either coming from a custom power supply or DMX console; listen to that information, translate it, and send it out to the proper LED, to say “You’re going to be on at this much.”

There’s a method called pulse width modulation where you can actually turn it on and off. If you turn it on and off 100% of the time then You’re going to be at full. If you turn it on and off 50% of the time then it will appear to be half intensity.

Other manufacturers use different technology to do it so there’s multiple methods of controlling the LED. Essentially what You’re looking at is, they are reaching the point where they will become useful as lighting fixtures, from a distance.

When I teach my classes, the first level of breakdown as far as basic lighting, deals with the differences between a spot fixture and wash fixture. A spot fixture can actually focus an image, so you have a pattern or a gobo that you can shoot onto the stage; and you can also do a sharp focus. The rest of the fixtures; the PAR, the Fresnel, cyc lights, are all wash fixtures. You can never get a sharp edge out of them. At the moment, LED fixtures fall into the wash category. There is not a sharp edge on them at all.

TFWM: : So you couldn’t use an LED as a spot?

SE: Well no, because you can’t get a sharp edge on it. They’re getting to the point that you can throw them a good distance, so you could use them in place of a PAR. I can’t use them in place of an ellipsoidal reflector spotlight. Ellipsoidal reflector spotlights right now are still the only fixture with sharp edge control. You have to have them and you have to have a dimmer to control them. Now with the LED, I can replace the PAR fixtures and the cyc fixtures.

The other trick is, LEDs come with built-in color changing, so the PARs that either need a scroller or 3 or 4 PARs to get multiple colors, are gone. If you have to use a color scroller, you’re going to have a string of colors, so if I want to go from color red to color blue-green, you might have ten colors in between that on a scroller. If I don’t want people to see that I’m doing that, I have to turn the light off and then turn the light back on again after I move the scroll.

Same thing with dichroic filters. Even with dichroic color fixtures like the Nexera by Wybron, (They’re moving dichroic filters), I have more color choices than a scroller, but I still have the same issue if I move from one color to another I’m going to see it. LED’s can fade from one color to another with very little color shifting in between colors. There is an issue with LED in that because we have an array of colors within the fixture, if you don’t put any diffusion in front of the fixture, (diffusion will block the light) you will get multiple color shadows. The red and the green and the blue are not coming out in exactly identical planes. If I have an amber coming out of an LED fixture, I’m going to have a shadow which has red in it without the green, or a green shadow without the red in it. If you add a little bit of diffusion, you’ll blend the colors better but you’re going to lose a little bit of light.

Tune in next issue when we discuss the ways in which LED technology is changing the lighting industry.