Steve Mesh on the Building Blocks of Tunable White, Part 1

Guest post by Steve Mesh

Tunable-white and other forms of color-changing lighting have added an extra dimension of capability, flexibility, and complexity to the lighting industry. It’s almost as though we’ve gone from a 2-dimensional world to a 3-dimensional world based on the added complexity of controlling the luminaire’s coloration (typically measured by Correlated Color Temperature ) separately from the luminaire’s lumen output. Don’t be scared! Even though this has exponentially increased the complexity of the equipment and technology, you still don’t need a PhD in lighting to understand this new landscape.

For starters, how can you produce a variety of CCTs from the same luminaire? Answer – use a Light Engine (which are the LED’s on a circuit board within the luminaire) that contain separately controllable multiple “primaries” (colors). Many fixture vendors now offer tunable-white fixtures with two sets of LEDs on a single Light Engine. For example, one set might produce a primary color of 2700K (warm) and the other set might produce a primary color of 6500K (cool). If each set can be controlled – and more importantly, dimmed – independently, then the output of each set can vary. As a result, you can achieve any CCT and LED output intensity in that range. The range might be more limited. For example, the LED primaries may be 3000K and 5000K. This selection depends on what the application demands and what you want to achieve with the tunable-white luminaires. To help with “circadian entrainment”, typically higher CCTs are required (e.g., up to 6500K). These higher CCTs are at the cooler (blue) end of the visible spectrum. Note – “circadian entrainment” is the synchronization or alignment of the internal biological clock rhythm, including its phase and period, to external time cues, such as the natural dark-light cycle. In simple terms, it is the way that our internal clocks are reset to reflect the natural periods of day and night that occur in our environment. Entrainment can impact the overall timing of sleep and wakefulness. It may also have a role in limiting the overall length of sleep episodes.

Regardless of the CCTs of the LEDs, if only two primaries (colors) are used, and they both lie on the blackbody locus on the CIE chromaticity diagram, then any point in a linear line between those extremes will produce colors that deviate from the blackbody locus. Colors on the blackbody curve match the color output based on heating an object from a process called incandescence. So, if the desire is to produce CCTs that match the blackbody curve, a different method must be used. One method is to use luminaires with three primaries (colors) – meaning three sets of primary LEDs on the Light Engine. This creates a triangle on the CIE chromaticity diagram – and within this triangle you can fully contain the blackbody curve for that range of CCT output, typically with a boost to CRI.

Obviously, that decision alone affects the complexity of the equipment you select as two-primary LED Light Engines are more common than three- or more-primary Light Engines. Incidentally, there are luminaires in the market that use five or even seven (or more) primary colors of LEDs. How can you, as a specifier or owner, manage this level of complexity to produce the color you want? Not by directly controlling each set of LEDs – that’s for sure! What are some methods you can use to get the control you need over this color-changing equipment?

Seemingly, the simplest form of control for tunable-white lighting is the use of two 0-10V wallbox slide dimmers. One controls the intensity and the other controls the CCT. However, in this case, these 0-10V dimmers do not directly control the LED Light Engines. They are connected to a device that takes each signal and then translates those into dimming signals for the two (or more) channels of colored LED sets. This sounds simple, and perhaps inexpensive. However, remember that this requires running low-voltage wires from the wallbox devices to the luminaires.

Additionally, because these are low-voltage analog signals, longer wiring runs and the resulting voltage drop could have a dramatic impact on the coloration and intensity output from fixture to fixture. You wouldn’t want that in your space. This is also not a “systematic” way of providing lighting control. It uses wallbox dimmers connected to switch legs almost the same way as any other wallbox dimmer would. So you don’t get the benefits associated with using networked lighting control (NLC) systems.

You might want to make the jump to lightspeed – by accepting that the complexity of tunable-white lighting deserves a digital NLC system. Once you do that, there are a variety of benefits. One is that every fixture in the space can be commanded to behave in exactly the same way in terms of intensity as well as CCT. Because these are digital signals sent throughout the network, there shouldn’t be any deviation in appearance due to signal degradation as voltage drop due to long runs of low-voltage wiring is eliminated. Another benefit is that a digital NLC system can typically handle bi-directional communication, so if a particular fixture or zone (or anything else) is not performing as desired, or not working, you should know about it instantaneously. As a protocol, 0-10V is notoriously imprecise. So even if the two 0-10V slide dimmers first talk to a “mixing” device that tells the LEDs what to do, how do you know what it really means if the slider is, let’s say, in the middle of the slide range? For example, if you have tunable-white fixtures with two primaries – 2700K and 6500K – and you pull the slider for CCT control down halfway, does that automatically mean that the luminaire output is now 4600K (the midpoint between 2700-6500K)? There’s no way of knowing! The same would apply to the question of intensity! If you have been keeping up with LCA blog posts in recent years, then I’m sure you know that one of the biggest reasons to use a digital NLC system is that the zoning is created in the software and is not determined by hard-wired switch legs! Whether you are deploying tunable-white luminaires or not, this flexibility in zoning (and re-zoning) is a huge benefit to using a state-of-the-art digital NLC system.

As a specifier or a user, which would you rather say? 1.) “I want the cheapest technology I can find, and I if I pull the slider down halfway, I hope I’ll get the median CCT (or intensity for that matter), without feedback from the luminaires.” Or … 2.) “I want to be able tell the lighting controls exactly what CCT and intensity I want, and know that I’m getting the results I asked for, and I want to see a confirmation of that.” I hope you would opt for the latter. It’s not hard. But it requires that you use a digital NLC system of some sort.

Luckily, many networked lighting control systems offer CCT control as a standard option in their software. For example, the DesignLights Consortium Qualified Products List has entries for 50 different NLC systems. Out of those 50 systems, 22 of them indicate that they have some form of control over color-changing luminaires.

You may ask … how do the other building blocks of a tunable-white or color-changing system work? What do they do? And how do they interface with lighting controls? What protocols are used by different components in a tunable-white system, and why? Some are open, and some are proprietary. Why do some vendors use one as opposed to another? These are all great questions! But we are out of time for now. Those will be the subjects of future blog posts. Stay tuned!