LED fixtures eliminate the need for dimmer packs…This is an oft repeated mantra; and while it’s true, this does not mean that LED fixtures are plug and play products, at least not if you want to control them fully. As Stephen Ellison, Lighting Designer Stark Raving Solutions, explains in this interview, controlling LED fixtures requires sending them data signals from a DMX lighting console. Ellison a highly regarded church and theatre lighting professional breaks down the process for us.
This may be a broad question, but in a nutshell why you think LED technology has been adopted by so many churches, theaters and others?
“The simplest answer is color, politically correct answer is energy savings. The ability to have one fixture produce so many colors is a blessing. Just looking at back lighting as an example. In a standard theater plot you would have 5 fixtures to cover a 40’ wide stage on a pipe. In order to have color choice you would add two more fixtures at each location for a total of 15 fixtures on the pipe. If the stage is 30’ deep then you would have 3 pipes for a total of 45 fixtures at 575 watts, or a total of 25,875 watts, which equals 215.625 amps. Now with LED fixtures you can use just 15 fixtures, which will provide more color choices and only use 1800 watts, or 15 amps.
“Color choice improvement is huge with LEDs since with the 3 fixtures you can only create a limited range of colors. With LED fixtures now that have RGBAW-Lime you have a huge pallet of colors. The only drawback is that you are also limited in the very saturated blue range, but within the range of blue that you do have you will get more intensity than you ever can with a normal PAR fixture.”
Everyone knows LED fixtures eliminate the need for dimmer packs: can you explain why?
“LED stands for Light Emitting Diode, a diode is an electronic component that is controlled by an electronic driver circuit. So good driver circuits have the dimming control built into them. What you need to provide the fixture with is just power which can be controlled by a switch. In order to have complete control over a fixture you also need to send it a data signal from a DMX lighting console. You can have fixtures work locally or by sound as well.”
Although they eliminate the need for dimmer packs. LED systems do create other demands when it comes to controlling them. Can you elaborate on this?
“When DMX 512 was first introduced the idea of using all 512 channels was unimaginable. I mean who would need 512 dimmers? Now filling up a universe (512 channels) is very easy. The way to understand this is to think about lighting fixtures as having attributes, and each attribute requiring a DMX channel. So an incandescent fixture connected to a dimmer has one attribute, Intensity. An LED fixture that has Red, Green, and Blue colors has a minimum of 3 attributes, one for each color. You could also add an overall Master Intensity to bring the count to 4 channels. This is a simple fixture, when you begin looking at more complex fixtures the attribute count can go up quickly.
“So in order to control all of these attributes we need to be able to send our data from the console to more than one universe. Also we are sending the data to every fixture, before we only had to send the data to the dimmer rack, one run, now we have multiple runs. DMX 512 also has limitations that you have to remember when you are sending data around the building. First, you can only talk to 32 fixtures from a console driver chip. So in order to talk to more than 32 you have to split the signal using an electronic box that takes in the console data and retransmits it multiple times thru optically isolated outputs.
“The good news is that you can split the signal this way indefinitely. However, since we have a 512 limit per universe you won’t split it too many times before you need another universe. The next way to send data is across a network, which will allow you to send at least 64 universes over a network cable. The thing to keep in mind is that network wiring rules apply so you are limited on any run to 100 meters from switch to switch. When you are using a network you will use a node to switch from Ethernet protocol back to DMX 512. So data network design is becoming more complex, which means you will need to learn how to setup a computer network.”
What is the most common mistake end users make regarding the control of LED fixtures?
“Setting the fixture to the highest channel count available. Going back to the attribute model, every fixture has a list of available attributes. Also every fixture has a built in microchip so that it can understand the DMX 512 signal. In the programming for a fixture the manufacturer provides you with options for how you will use the attributes. These choices are provided in DMX charts, a very important document to have when programming. In the case of our simple wash fixture, RGB, we could have options for 3, 4, 5, and maybe 7. Beyond the simple control over each color, we can add a strobe channel, a pre-built color mix, and our master dimmer. The big mistake is just picking the highest channel count for everything and then running out of room in your universe. When you go to buy your lighting console you will find that the cost is tied up with how many channels you have available.”
What advice would you give a church or theatre that is replacing its incandescent fixtures with LED products?
“Add a method for turning off the power to the fixtures when you are not using them. Remember even if there isn’t any light coming from the fixture it is consuming power. While the LED’s are rated for 50,000 hours, they are connected to electronics which also have a life cycle, and leaving them on 24/7 isn’t all that good. Lastly do not use anything but cable designed for transmitting DMX, no microphone cable. DMX is a high speed digital signal and needs a cable designed for that purpose.”
For more information visit: www.starkravingsolutions.com