Guest post by C. Webster Marsh, a lighting design controls specialist at HLB Lighting Design in Boston, MA. His views do not necessarily reflect those of HLB.
DMX-controlled tunable dynamic white luminaires are luminaires that use DMX controls to change their correlated color temperature (CCT) on demand, which provides a dramatic design tool to the modern lighting designer. These luminaires are different from dynamic color changing luminaires because instead of using colored LEDs, they use a mix of white LEDs such as warm white, neutral white, and cool white. When these hues are mixed at different intensities, the overall delivered CCT of the luminaire changes. It is very important to have a robust controls system specifically designed and programmed for the control of tunable dynamic white luminaires. Any compatible controller will control a DMX tunable white luminaire and can adjust from one hue to another, but that’s only half the story.
What is DMX
Digital Multi-Plex (DMX or DMX-512) is a common controls protocol for dynamic lighting. The DMX protocol originated in theater where there were only static white luminaires with rooms full of dimmers to control them. The original intent of digital controls in theater was to control individual dimmers while reducing the number of wires running back to the control console. Since then, DMX has become the standard for theatrical controls. The expanded capabilities of modern DMX allow the control of luminaires with unique features such as color changing, panning/tilting, and beam shaping, to name a few. The current success of DMX in theater is owed to the intricacy of the control consoles, the expansive controls system infrastructure, and the incredible amount of time dedicated to programming each show, which can take weeks to complete. While it has been associated with theatrical controls for a long time, DMX is becoming more common in architectural projects due to the increased use of dynamic color changing luminaires on architectural projects.
DMX uses unique addresses and intensity values to control luminaires. Each dimmer on a DMX system will have a unique address from 1 up to 512. Luminaires with more features, such as color changing, have one unique address per feature. For instance, an RGBW luminaire will have 4 unique addresses, one per color. The intensity values can range from 0 to 255, but typically this range is expressed as 0% to 100% on an end-user device. Each address has its own intensity values, so the address for red dims independently from green, blue, and white.
Tunable Dynamic White in DMX
Controlling tunable white with DMX is no different from controlling any luminaire on DMX. There is one unique address per feature, in the case of tunable white it is one address per individually controlled set of white LEDs. To set a static white, each colored LED is adjusted in intensity until the desired overall kelvin white is produced by the luminaire. The caveat is that dimming the luminaire’s intensity will change the hue if all LEDs dim at the same rate.
For example: A 3 color tunable white luminaire has a warm, neutral, and cool LED. If the warm LED is at 100%, the neutral is at 50%, and cool is at 25% and all three dim down linearly by 25%, the warm LED will now be at 50%, neutral will be at 25%, and the cool will be at 0%. Because of this, the intensity of the luminaire will be decreased by approximately 25%, but the overall hue will have shifted warmer.
To overcome the limitations of linear dimming, the DMX controller often has an algorithm to treat hue and intensity separately. Many RGBW luminaire manufacturers provide software profiles for their luminaires. These profiles have fixture specific algorithms to adjust the DMX intensity values of each address. With these profiles, hue is maintained while intensity can be lowered. If no profile exists for the luminaire or tunable luminaires of different manufacturers are on the project, then it is recommended to have a skilled programmer on the construction team.
How to Specify DMX
DMX is a good option when specifying a tunable dynamic white light, but some coordination and a good controls system are required. At minimum, the following should be specified for tunable dynamic white luminaire controls systems:
1. A DMX controller
2. DMX software
3. A manufacturer created software profile for each type of luminaire or extra time for programming on site
4. A programmer
5. Time for installation and programming
A lighting controls designer specifying tunable white should always consult a DMX controls manufacturer and the manufacturer of the luminaire to specify the best solution, which may include multiple days of on-site programming by a factory certified technician. There are systems other than DMX that are designed to control tunable white luminaires, however, so DMX controls shouldn’t be the only option considered. Controls designers have many tools at their disposal right now each with their own best applications, so it is recommended to become familiar with all options before deciding on one.