As users make the transition from traditional halogen/incandescent globes and downlights to solid state lighting they are faced with compatibility issues between LED lights and their legacy dimmers. Flicker, limited dimming range and dead travel are all issues that can occur as a result of an imperfect dimming system. This article discusses the various options for complete SSL dimming solutions.
Some LED drivers, like the unit supplied with Starlight's 12W LED Downlight come with a 1-10V analogue dimming interface. These can generally be controlled either by a 100 Kohm potentiometer or via a current sinking 1-10V control signal, as is offered by C-bus, Clipsal's popular home automation system. Given that a wall-mounted potentiometer connected to each downlight driver in the ceiling would no doubt come with some wiring issues, the 1-10V dimming option is explored as an option in the scope of a C-Bus system.
A basic C-Bus home installation consists of a network of independent C-Bus units that communicate via a 36VDC, two-wire bus. All units besides C-Bus power supplies and relays are also powered from the 36V bus. Unit inputs and outputs are assigned addresses so that control messages can be broadcast via the C-Bus. Units mapped to those addresses will then respond. Communication via a common bus therefore facilitates complicated inter-unit synchronisation and control via simple wiring. The single bus system also makes reconfiguration of the automation network simpler as rewiring is not required.
C-Bus is a popular home and building automation solution due to it's broad range of interfacing units and reliable low-voltage method of signal transmission. Clipsal have developed C-Bus units for several of the most common dimming control methods, including triac or phase-cutting, 0-10V analogue and DALI.
A basic C-Bus lighting system would require the following units:
Total Cost: $1,890, excluding additional power supply and motion sensor input
Installation and Maintenance
C-Bus home installation would require a licensed electrician who is familiar with C-Bus. Although a computer is not necessary for normal C-Bus operation, system configuration and linking input units (motion sensors, switches, etc.) to output units (dimmers and relays) is initially programmed through a PC interface.
The C-Bus network consumes additional energy. The energy consumption vs energy savings depends on the size of your system and the controlled appliances. Considering only the lighting module, each C-Bus unit draws 18 mA from the network. The switch, analogue controller and relay will therefore draw a total of 54 mA from the 36 VDC C-Bus network, 2W. A more likely number of connected C-Bus devices for full home automation, say 20, would be 360 mA, totalling 13W. Comparing this to the power consumption of other appliances like a/c, lighting and television - it is largely negligible compared to the potential energy savings.
Control and Performance
The modular nature of a C-Bus configuration means that control can be be implemented through a variety of interfaces. Switches, remotes, motion sensors, light sensors, or web-enabled devices like smart phones, laptops or tablets can all be used as a means of lighting control. The draw-back of this is that each option can introduce an additional cost of at least $200, since the added input unit must be C-Bus compatible.
As with other systems, the dimming performance of the lights remains highly dependent on the luminaire, driver and dimming method combination. For a performance comparison between phase-cut and 1-10V dimming, the dimming profile of Starlight's 12W LED Downlight for both methods can be seen in the below figures.
In the case of Starlight's LED downlight kit, dimming performance was not remarkably different between methods. There was some improvement in the dimming range, while phase-cut dimming was only able to dim to 10% brightness, the 1-10V interface allowed dimming down to 0%. There remained a significant amount of dead travel in the upper range for both dimming methods, however the use of an adequately programmed C-Bus analogue output unit would likely make flat areas in the dimming profile unnoticeable.
While switching to 1-10V dimming LED drivers may potentially improve the dimming range, the initial cost of a simple C-Bus lighting system probably does not make sense unless the user already has a C-bus system installed and wants to integrate LED lighting into a network to make further use of existing sensors and switches.
There are a variety of wireless lighting system options. One such option endorsed by the major lighting manufacturers including Philips and OSRAM is the Zigbee Light Link (ZLL) system. The Zigbee Light Link standard was developed to ensure interoperability between emerging wireless lighting products and to provide native support for lighting features such as dimming and colour variation.
A few retrofit products that use ZLL like the Philips Hue and OSRAM's SYLVANIA ULTRA iQ LED BR30 intelligent lamps are currently available. These bulbs implement integrated dimming and, in the case of the Philips Hue, integrated colour change for further ambient lighting control. The limitations of the most readily available ZLL products on the market are their price point (Philips' Hue starter kit is approximately $200 for three 600 lumen bulbs and a wireless bridge), the current lack of ZLL compatible downlights/drivers and the limited number of ZLL products currently available.
The ease of installation compared to wired systems makes this a particularly attractive option. Other wireless systems such as wireless C-Bus already exist, however as discussed earlier, C-Bus only appears as an economically feasible solution for LED lighting if the user has already invested heavily in a complete C-Bus home automation system.
Other wireless lighting systems such as the Wifi-based LimitlessLED are much cheaper, however it faces the difficulty of competing with big lighting manufacturers whose high speed of innovation and increasing interest in Zigbee implementations will likely render other wireless LED dimming systems unsuitable when interoperability is required. The dimming profile of the limitlessLED using a wireless remote is shown in the figure below. Although it does not dim continuously, it has 11 dimming levels and possesses a smoother profile than most LEDs using phase-cut or 1-10V dimming controls. While the LimitlessLED maintains 5% light output at the lowest dimming level, the light can be reduced to 0% output by putting it on standby with the remote and therefore essentially has 0-100% dimming range.
AEG Power Solutions have a line of Zigbee-based modular lighting controllers for interfacing with lighting drivers via 1-10V analogue, PWM or DALI. ZLL control products like this can greatly expand user's options beyond a limited range of specialty retrofit globes and render wireless controls compatible with a user's preferred LED kit. At the time of writing this article however, AEG's ZCM series controller does not appear to be readily available to the public.
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