MH Controls Corner: DMX Lighting

With new LED technology allowing color changing and color tuning, the use of advanced lighting control protocols is becoming more widespread for architectural lighting. The DMX control protocol has been used in theatrical lighting for many years. Architectural lighting manufacturers are now using this protocol on color changing or color tuning fixtures, and many architectural lighting control systems are now offering components to allow a DMX interface for these fixtures. Following is some general information on the advantages and design considerations of DMX control.

Advantages

• The DMX protocol allows individual fixture addressing. This allows control of individual fixtures, groups of fixtures, or all fixtures on a system, based on what is needed for specific applications.
• Fixtures with DMX offer full-range dimming and color changing control that is consistent across all fixtures on the system. This delivers more consistent and reliable results compared to many manufacturers who utilize dual channel 0-10V control for color tuning fixtures. The problem with this non-DMX approach is in the voltage drop that is inherent in the 0-10V control wires. While the human eye does not perceive enough difference in dimmed levels for this to be a problem, voltage drop in the color control wiring can create noticeable differences in color temperature for different fixtures in the same space.
• A single control wire is used for the control of multiple fixtures.This eliminates the need for a wiring home run for each control zone in a group.
• The DMX protocol is based on established ANSI and USITT protocols, allowing consistency and compatibility between numerous fixture manufacturers and control systems.
• There are a variety of options for wireless DMX transmitters, allowing installation in both interior and exterior applications, where the installation of wiring is difficult. This can be particularly useful for retrofit applications.

Design Considerations

• The DMX protocol is based on “Universes” that include 512 channels of control information. DMX fixtures use multiple channels of control. An RGB (Red, Green, Blue) fixture will typically use three channels of control, one for each color. An RGBW (also includes White) will typically use four channels of control. Color tuning fixtures typically use two channels of control. Some control systems are capable of transmitting multiple universes of control, but the channel limitation must be considered.
• Cable length is limited to 1,500′ total. While this is a very robust distance, extending cable lengths beyond this distance could cause communication problems and unpredictable behavior. Fixtures are connected in a daisy change topology with up to 32 fixtures per run. Splitters and optical isolators can be incorporated to increase the transmission distance and the number of devices that can be controlled.
• Additional controls programming is required for a DMX system.This programming includes the addressing of each individual fixture, as well as the programming of the control system. Additional time and expertise is necessary to make these systems operational.
• More advanced user interfaces will be required to get the full capabilities of the system. Options range from simple pushbutton controls that create static colors, touchscreen interfaces offering a nearly infinite selection of colors and dimming, or more advanced computer-aided programs that allow time-based fixture chase scenes, where colors and levels will change in a sequence over time. It is important to consider the desired system functionality, as well as the potential programming complexity for end users to make changes after the initial system programming. Adding a color changing fixture without definition of the functional needs of the system causes confusion throughout the construction process, and may ultimately result in a system that is not capable of meeting the needs of the end user.

MH has a full range of color changing and color tuning lighting, and associated control systems to fit any application, from the most simple through full theatrical systems. Contact any member of the MH Controls team for assistance with designing or installing your next system.

This article was written by Clint Conley, our Lighting Controls Department Manager. Clint can be reached at 720.904.8554 or clint@mhlighting.com.