araya® - a profound advance in illumination recognized by the industry with several innovation awards. And now extended to a family of modules , each delivering the highest quality of tunable light with a uniform complement of unmatched features and controls. araya® promises virtually unlimited applications to enhance every segment of the lighting market.
The five core elements of araya® are described below. This is lighting's new frontier and next revolution – the realization that electric light can replicate sunlight.
The number of control channels deployed in a color tuning system impacts the quality of the light and consistency of color. It also affects the color tuning range, the level of gamut control and the efficacy of the solution.
Intuition correctly suggests that increasing the number of channels and colors will provide more control, fuller spectrums and improved CRI. The original three-channel RGB systems, or even commercial three-color systems that replace primary colors with broad spectrum phosphor-converted (PC) LEDS, provide basic color control but with very poor color quality due to the large spectral gaps between the pure red, green and blue colors. In practice, most commercial multichannel systems today do not use simple primary colors.
araya® mixes five different colors of high brightness, broad spectrum LEDs – none of which are white – to deliver light that is 2 SCDM about the Planckian curve at 90+ CRI across the tuning range. The use of a ‘no PC white’ five-channel architecture requires sophisticated software to manage the complex response of the LEDs over a wide range of operating conditions. In a five-channel system, each color needs to be separately characterized and monitored for changes due to aging, thermal effects and power levels.
The result: light that accurately depicts – across the full tuning range – the object’s color as compared to its color in true sunlight.
On-board Driver Electronics
Color tuning systems have two basic components: the multichannel LED driver and the multichannel LED array. The driver typically uses a combination of current control and pulse width modulation (PWM) to modulate the different color channels and maintain a smooth dimming profile. One of the challenges for both fixed white and color tuning systems is the introduction of “jitter” or jumpiness in the dimming profile as dimming levels approach 1% and lower. Drivers and control systems have to provide smooth transitions and minimize visual artifacts across the range of use conditions.
Pairing the appropriate driver and LED requires compensating for the intrinsic LED-to-LED and driver-to-driver variability. Fixed white solutions typically rely on LED mixing to average out these variations so that standard drivers can be used. The intrinsic variation in LEDs is more challenging when assembling color tuning solutions. These constraints represent a complex problem, and it is not practical to characterize and optimize each light source after fixture assembly.
Color tuning systems must provide both a smooth dimming profile and maintain CCT and color quality over the dimming range. Poorly controlled PWM systems can create significant “flicker” with stroboscopic effects that can be harmful to health. Modulation is less impactful to health at frequencies greater than 1KHz, but its effect becomes increasingly problematic at lower frequencies. PWM control architectures for color tuning need to stay clear of these harmful flicker ranges and avoid jitter as they are dimmed, all while maintaining high quality color over the tuning range of the source.
Each individual color tuning light source is inherently unique due to the underlying variability of the LEDs and the complex, nonlinear interactions of the systems components. For fixed white LED systems, the industry standard data sheets are generally sufficient to predict the behavior of the LEDs. Color tuning systems are operated dynamically which means that industry data sheets are not sufficient to predict LED behavior, and fixed look-up tables must be supplanted by active feedback. Thermal and optical feedback sensors add to the control complexity as they also need to be calibrated for a given driver and LED array to assure proper response.
Given the unique and complex nature of each color tuning light source, drivers and LED arrays should be provided as factory -matched and calibrated sets. If the LED array and drivers are provided and assembled separately, the fixture manufacturer must run each fixture through an elaborate integrating sphere test and calibration sequence. The only scalable solution for color tuning systems is to integrate the driver with the LED array, so that it can be tested, optimized and supplied as one piece which meets the specification over the life of the source.
Integrated (LED array and driver) color tuning light sources have additional advantages for users, designers, installers and fixture manufacturers. The color points and dimming profiles of integrated light engines can be customized through software changes, thereby reducing multiple hardware SKUs typically required for fixture manufacturers. Integrated drivers can be lower cost than independent drivers as they share packaging and a common processor, and the drive channels are matched to the LED loads. Running low voltage power to multiple fixtures rather than high voltage with separate step-down transformers for each fixture can significantly reduce installation costs. The presence of a low voltage source in each fixture can also provide the power needed for additional sensors such as occupancy, daylighting, and indoor positioning.
Integrated driver and LED arrays enable low cost, standardized, accurate and stable color tuning solutions.
Closed Loop Optical and Thermal Feedback
It is well known that light output from LEDs decreases with operating lifetime, commonly called “lumen depreciation”. White and the various color LEDs decay at different rates, depending on the amount and type of phosphor used along with the type of process by which the semiconductor layers are deposited. For instance, blue decays the least and red the most, with the other colors and whites falling in between. To compensate for this, araya® color tuning modules have a closed loop optical feedback system that constantly samples the light output from the various LED colors. Measured flux values are regularly compared against stored initial factory values. If the error exceeds a threshold value, the compensating algorithm adjusts the string currents so that the initial color points are maintained, but of course with lower output due to lumen depreciation.
The luminous flux output from all LEDs drops with increasing junction temperature, commonly called “thermal droop”. The flux from white and the various color LEDs decrease with increasing temperature at different rates, depending on the type and amount of phosphor used along with the deposition process of the semiconductor layers. The junction temperature, in turn, varies with ambient temperature, the current passing through the LED string, the CCT being requested, the amount of dimming, and other factors that affect the heat transfer from the junction to ambient.
To compensate for this, araya® Color Tuning Modules also have real time, closed loop thermal feedback that monitors the LED junction temperature and feeds this and the other requested parameters to the micro-controller as inputs. The thermal compensation algorithm uses these inputs and generates the LED string currents that satisfy the input demands, while maintaining high color quality such as CRI, R9 and ΔUV over the full CCT tuning range. In the event of excessive operating temperatures, the on-board thermistor can be used to maintain the LED junction temperature within specification and prevent irreparable damage.
In-Line Spectral Capture and Custom Color Model Generation
Binning systems were developed to mitigate intrinsic LED variability and enable predictive assembly of fixed white solutions. For color tuning systems, industry standard LED bins and data sheets provide limited value. Color tuning systems that mix LEDs based on bin characteristics are subject to variability well outside the high quality light criteria (less than 2 MacAdam ellipses).
The optimal solution for characterizing and operating a color tuning system is to capture the spectra of each LED and generate a unique color model for each and every light engine. This custom color model approach unlocks the full potential of each unique LED array and thereby eliminates the efficacy and performance penalties of worst-case bin based color models. Furthermore, this methodology enables the optimum use of off-Planckian LEDs like high-efficacy PC lime, which dramatically improves the efficacy and performance of color tuning light sources. Custom color models with off-Planckian LEDs can increase output and efficacy of tunable light sources by as much as 20% to 30%.
This approach requires in-line spectral capture of the combined LED, driver and diffusing element over a range of color, power and thermal conditions. The resulting data set is then fed into a color model algorithm to calculate the optimal solution for every color point in the tuning range. This methodology generates a unique, programmable color model for each light engine that can be optimized for color, efficacy and other user specified parameters. There is no additional material cost in the product with this approach and the testing time is equivalent to any traditional calibration scenario.
For color consistency, the in-line spectral capture methodology enables a color point match of less than 2 MacAdam ellipses across the color range.
Unlocking the functionality enabled by high quality color tuning light sources requires addressing the ecosystem in which light sources are used. Controls solutions must balance the need for compatibility with existing protocols while providing access to new functionalities enabled by color tuning light sources. Color tuning devices must be backward compatible to today’s lighting ecosystem yet also enable the transition to wireless controls and the Internet of Things.
The lighting industry is served by a variety of control protocols that have evolved to serve particular applications and regions. Legacy protocols range from simple 0-10V controllers and triac-based dimming in the United States, to DALI controls in Europe, to the more elaborate DMX controls common in theatrical lighting. Some control companies favor open architectures while others promote closed proprietary systems (Lutron, Schneider Electric and Color Kinetics). New control platforms are emerging to take advantage of the availability of low cost wireless communication (Daintree, Enlighted). There are several wireless platforms in the market, such as Bluetooth low energy, Zigbee, WiFi and EnOcean.
The controls market is fragmented and therefore presents a challenge for light source and fixture manufacturers, as well as lighting designers, specifiers and users. Matching light sources to control protocols adds cost and increases SKUs for the industry. The new functionalities of color tuning light sources add new complexity as most existing protocols are designed only for on/off and dimming.
Fortunately, the digital intelligence embedded in high quality color tuning light sources offers the interface flexibility required for most common control scenarios. As the lighting control ecosystem evolves, a two-path strategy is the preferred solution for controlling high quality color tuning light sources. Serving existing renovation and new build projects requires light sources that are compatible with existing protocols. This first order requirement is managed by designing light engines that are compatible with triac, 0-10V, Dali, Lutron and DMX. Color tuning functionality can be controlled using these traditional protocols by translating conventional signals such as dimming into color commands. For example, conventional 0-10V dimming signals can be changed to control CCT, drive a warm-dim profile, or trigger preset color points. While compatibility with existing control protocols enables fixture manufacturers to control color tuning, it does not unlock the full functionality of high quality color tuning systems. Providing a second but direct control path to the light source allows the fixture manufacturer, lighting designer and end user to access the full complement of features enabled by digital color tuning light sources. One attractive alternative to PLC is a direct wireless path to the color tuning light engine. The primary wired control remains the first priority, but when a manufacturer, installer, lighting designer or user needs direct access, this wireless channel is available.
This two-path approach is particularly valuable when the light fixtures are being commissioned in the field. A smartphone-based commissioning tool can tap the full functionality of the light sources, access the operating conditions and history of the light source, and change the firmware and color model. This two-path control strategy affords the compatibility and flexibility required to maximize the value of color tuning light sources in today’s control ecosystem. Importantly, this approach also ensures that fixtures will be compatible with future developments and the impending ‘Internet of Things’, where enhanced connectivity is desirable.