Steve Mesh on the Building Blocks of Tunable White, Part 2

Guest post by Steve Mesh. Check out Part 1 here.

The previous post on Tunable-White Building Blocks talked about differences between using low-level analog control technology as opposed to networked lighting control (NLC) systems that employ digital communication between components. Analog technology such as 0-10V dimmers can in fact be used to control certain color-changing luminaires. Let’s be specific about which types. There are actually three main types of color-changing lighting systems – “dim-to-warm”, “tunable-white”, and “RGB.”

Dim-to-Warm
These luminaires are designed to mimic the change in CCT that occurs when dimming incandescent lamps. For example, one luminaire manufacturer offers “dim-to-warm” fixtures that produce 3000K at full output, then decrease to 2000K at the lowest end of the dimming range. Typically, luminaire manufacturers state that any dimmer can be used to control their “dim-to-warm” products. In some cases, vendors also state that any LED driver can also be used. What does that tell us? Automatically, that means that the “brains” controlling the change in CCT must be in a separate component located downstream of the driver, housed internally in the fixture (or in the LED array itself).

The correlation between the dimmed light level and CCT is pre-configured and stored in the component with the “brains” – the “Dim-to-Warm Module” as shown in the diagram above (from Axis Lighting). Therefore, you can in fact use any available 0-10V driver, with a companion 0-10V dimmer. Keep in mind that with dim-to-warm, it is not possible to adjust the CCT separately from the intensity. If the operational intent is to be able to adjust intensity (think daylight harvesting) while maintaining 4000K, for example – then “dim-to-warm” would not be the appropriate solution as both CCT and intensity always change according to a pre-programmed correlation between the two. Incidentally, notes on spec sheets for these products say that these dim-to-warm luminaires follow a linear dimming curve in the range of 3000-2000K as you pull the slider down. It is not clear, however, if this is based on using a dimmer and/or driver which also employ linear dimming curves. What if you want to have logarithmic response for “square-law dimming” (presumably using a driver or dimmer that are logarithmic)? Well, since this is a lot of specificity (!!!) and the spec sheets don’t get down to quite that level of detail – a quick call to the manufacturer should clear this up! Right? Moral of the story – if you have a question about anything at all related to color-changing equipment – ASK!

Tunable-White
As described in the previous blog post, most tunable-white luminaires feature two sets of LEDs – some warm and some cool. In theory, you could connect one 0-10V dimmer to one driver to control one set of LEDs (let’s say 2700K), and the other 0-10V dimmer to the other driver to control the other set of LEDs (let’s say 6500K). However, that’s not how these systems are designed. Just as with the dim-to-warm offerings that have “brains” located somewhere that correlate changes in intensity with changes in CCT – tunable-white luminaires typically also contain brains to allow for changes in intensity separate from changes in CCT. These brains are likely in a separate component located in the luminaire itself or as part of the lighting control system. In this case the 0-10V dimmers are used to signal changes in either intensity and/or CCT, but the component that actually tells the drivers and LED arrays what to do are the “brains” (usually this separate component).

As described in the previous blog post (include link to the Part 1 post?), there are drawbacks to using simple analog (0-10V) technology to effect these intensity and CCT changes. 1.) The 0-10V protocol is notoriously imprecise as it depends on the voltage to the luminaire which changes (degrades) based on wiring length. There are few standards that govern what it means when a slider, for example, is at a particular point of travel. 2.) Using 0-10V dimmers requires that you run wiring between the wallbox devices and luminaires. You can’t, for example, link these devices wirelessly. 3.) Because the connection between the control devices (in this case, 0-10V dimmers) and luminaires is hard-wired, that means that zoning is fixed and can only be changed by re-routing physical wires – unlike changes to zoning using software as is the case with every new NLC system.

Just as a thought experiment, let’s temporarily back up one step. Could you in fact use two separate 0-10V wallbox dimmers to control two totally separate LED arrays – let’s say one with 2700K LEDs and the other with 6500K LEDs? Sure. If you created such a home-made fixture in your garage, what would you have to do to get “full output” at a midpoint CCT (4600K)? Turn both wallbox dimmers up to full so you’d get equal output of the 2700K as well as 6500K LEDs? No (!!!). If you did, then you’d never be able to achieve the same output at any other CCT. So you can see why the “brains” that do this work for us are required in tunable-white fixtures – even if you use 0-10V dimmers to control two separate “channels” (in this case, “channels” means control over something such as intensity or CCT – not the different colored LED chip sets). In fact, these “brains” cap output at different parts of the dimming range for each LED array based on the desire to get full output at any CCT you select.

If your head hurts from that thought experiment, you’re not alone! That’s why manufacturers with very smart people have created these “brains” that are in the components already installed in the luminaire, so you don’t have to figure this out for yourself. Just remember that if you use 0-10V dimmers to separately control intensity and CCT, you’re still using devices that are notoriously imprecise in terms of what signals are being produced at which point of the slider travel (and lord knows what that will mean in terms of specific output of intensity or CCT). You’re also still locked into rigid zoning, and the need to run physical wiring between the wallbox dimmers and luminaires. It’s important to keep in mind what the client needs and wants. Analog 0-10V controls can be satisfactory, but digital communication between all components in a tunable-white system will always be the most robust in terms of capabilities, including future IoT requirements. So it may be preferable to use a fully digital system, realizing that in some situations, analog 0-10V controls for CCT and intensity changes may in fact be adequate.

Since tunable-white luminaires require “brains” somewhere in the system (for example in an on-board component within the luminaire), it’s pretty easy to send precise digital commands to those brains. There are some different “standard” digital protocols that are already commonly used for this purpose. The most well-known are DALI and DMX512. DMX is a protocol that was originally developed for use in the theater, where fixtures may have multiple attributes requiring control: 1.) changing color, 2.) rotating, tilting or panning, 3.) changing beam shape or size, 4.) dimming, 5.) incorporating gobos or color wheels, etc. In this new world of controls, those are called “channels”. DMX was developed to send signals telling any fixture what to do in terms of any of those attributes. Potentially, that’s a lot of information to communicate! So a digital protocol is perfect for managing that degree of complexity. Fixtures for architectural use, at least historically, had very few of those attributes except for the ability to dim. Now things are different. An architectural project might in fact use fixtures that can change color, but that can also be rotated, tilted, etc. Or where you can change the beam shape or size. Or aiming point if it’s an accent light. DALI (Digital Addressable Lighting Interface) was created to allow for sending digital commands to architectural fixtures with a more simplified wiring architecture. You can see why many fixture manufacturers are allowing for the use of either DALI and/or DMX in “architectural” fixtures. The lines between “architectural” and “theatrical” are getting blurred. And that’s all just semantics anyway. The real question is – what do you want your luminaires to be able to do, and what is the best hardware and software to achieve those results?

Once you decide that it makes sense to use an NLC with some form of digital communication, then all of the issues and limitations associated with analog protocols go away. 1.) You now have a system that uses precise communication – so if you want luminaires to provide let’s say 3250K CCT at 64% intensity, then that’s what you’ll get. 2.) The system may not even require wires to connect all components. For example, some manufacturers are now using “wireless” DALI, so you can connect to those devices without actual wires, but they still give you the benefits of the precise DALI protocol. 3.) Regardless of whether the connection is wired or wireless, actual “zoning” is created in the software and is not determined by physical switch legs.

Is that it? No, not quite. Sorry! As mentioned, there are a variety of digital protocols used by luminaire and controls vendors. Some are “open” protocols, like DALI and DMX. Others are proprietary. Even for an open protocol like DALI, there is DALI 2.0 Type 6 and DALI 2.0 Type 8. Which to use? Hmm. Would you agree that this is getting very deep-in-the-weeds? As previously mentioned, if you don’t know the difference between DALI 2.0 Type 6 and DALI 2.0 Type 8, then you simply have to ask. Don’t fret! Somebody out there knows all about this! Reputable luminaire and controls vendors probably do. And many knowledge sales reps and distributors do as well. If they don’t, then hopefully they can refer you to people who do. These choices may either lock you into or out of certain methodologies, fixtures or controls. So you still need to dot every “i” and cross every “t” when making these decisions. We could have a mind-numbing review of these possibilities right now, but that’s beyond the scope of what this post is trying to convey. Perhaps a future blog post will endeavor to untangle the differences between digital protocols.

RGB
No those aren’t the initials of a current supreme court judge! RGB stands for red/green/blue. These may also be called “color-changing” or “full-color-tuning” or some other such phraseology. These fixtures have three or more sets of LEDs of different colors. The triangle (or even a more complex polygon) created by these sets of LEDs typically covers a huge portion of the CIE chromaticity diagram. Therefore, it’s possible to produce light with a much greater range of hue, saturation and intensity than in a tunable-white luminaire.
With multiple sets of LEDs on the Light Engine, it should be obvious that these are considerably more complicated than systems that provide “dim-to-warm” or even “tunable-white” which operate in a very limited CCT range, which typically only allow for chromaticities along a straight line between two specific points. Obviously, by definition, the specific color in a full “color-changing” (RGB) system cannot possibly be controlled by the use of a slide dimmer – which can only provide variation between two extremes (e.g., 0%-100% output, or let’s say 2700K CCT-6500K CCT along a straight line). So these systems automatically make use of digital protocols.

As shown in this diagram and its associated table from the same Axis Lighting specification guide, there are a variety of options in terms of the type of digital protocol. You’ll notice that only “DMX – Standard” allows for control of brightness, CCT, saturation and hue. But that means you’re locked into DMX technology (control system) and topologies (wiring). If you want to use DALI, or perhaps another manufacturer of controls + drivers, then you need to make sure that the features of those protocols – and associated equipment – meets the needs of a given project.

It should be noted that some “tunable-white” systems use luminaires with three or even more primary LED colors, similar to how true RGB luminaires work. Of course, once you have a “tunable-white” luminaire that uses more than two primaries, the way that produces a specific color of light is already more complicated than a luminaire with only two primary LED colors. So you can see why it takes “brains” for the luminaire to figure out what to do – and why you need a control system with a user-friendly interface so you can clearly tell it what you want. Using two 0-10V analog slide dimmers does not cut the mustard once you start using more technologically advanced color-changing equipment! Please remember, however, that there are many tunable-white luminaires on the market that use only two primary sets of LED colors. Many of these produce a range of colors all of which fit within the ANSI C78.377 specifications. So if that meets your needs, that’s great. However, a particular project may in fact have demanding needs for more exacting color output even in a tunable-white application, in which case a system with three or more primaries of LEDs may be desirable.

Hopefully from this deeper dive into the driver side of the equation, you realize that there are huge benefits from using lighting control systems with digital communication between all components. Is this more complex than using simple analog controls (such as 0-10V wallbox dimmers)? Not necessarily. Remember that any type of color-changing luminaire requires some kind of “brain” somewhere in the system – even if you’re using 0-10V wallbox dimmers.

There’s even more detail about drivers for tunable-white and full-color-changing luminaires with new technology being introduced regularly. There are a variety of interesting features and benefits that are being baked into some of these new offerings – and you’ll want to hear about these cool new products (in an upcoming blog post). Stay tuned for the next installment about these building blocks.