You can use several different dimming options to dim LED Lighting. What are the possibilities and what dimming should you look from a LED driver? I’m going to answer these questions in this blog post by going through the different systems. The goal is to give you the basic understanding of the dimming methods available at moment.
I am grouping the dimming methods in two main groups: analogue and digital.
When you want to control lighting, you have to know some basic issues of your lighting fixtures:
- Are your fixtures dimmable? If yes, what is the dimming method which works together with your fixtures
- If your fixtures are non-dimmable, then you can only have on/off – function.
Analogue dimming covers all dimming systems that don’t transform the dimming signal into bits and controls the lighting in analogue manner.
Phase dimming systems dim the lights by altering the supply voltage.
Leading & trailing edge dimming
Before LEDs, we used to dim halogen lamps with wall dimmers. We can still use these kinds of dimmers. But dimmer, driver and LED-module must be compatible with each other. This type of control is accomplished without any need for an additional control wire. It involves connecting a dimmer in series between one of the mains wire and the equipment. The dimmer cuts part of the mains voltage sinusoidal waveform to a greater or lesser extent in order to dim luminous flux even from 1% to 100% (this value depends on dimmer and driver).
Depending on how the driver makes the mains voltage cut, it is possible to distinguish between two types of dimming:
Dimming cut-off in the wave on its ascending side, from the beginning (phase cut-off at ignition). This is traditionally used in halogen lamps supplied through electromagnetic transformers.
Dimming by cut-off in the wave on its descending side, from the end cutting backwards (phase cut-off at switch off). And this way of dimming causes less interference than leading-edge dimming.
There are dimmers and equipment that support both types of dimming, and others that support only one type.
The 1-10V system enables dimming of the luminous flux from around 1…10% to 100%. This is done by sending an analogue signal to the equipment over an additional, two-wire control line. These control wires have positive and negative polarities respectively and that must be kept in mind when wiring up the system.
The analogue signal has a direct voltage value of 1V to 10V. 1V or short-circuiting the fixture’s input control gives the minimum light level. While 10V or leaving the input control circuit open gives out the maximum light level. International standard, IEC 60929, defines the regulation curve. The regulation curve represents the relationship between the control line voltage and the luminous flux. It reflects a practically linear relationship in the range of 3V to 10V. To get a response adapted to that of the human eye it is possible to use logarithmically controlled potentiometers.
These in light fixtures generate power control with 1-10V dimming. Driver supplies a current to the controller through equipment control terminals. The controller current must be from 10µA to 2mA. The maximum control line current is obtained with a voltage of 1V and the minimum with a voltage of 10V. This dimming system is unidirectional, i.e. the information flows in one direction, from the controller to the light fixture. The latter generates no feedback to control. This means that this system can’t be controlled by a software. Groups have to be created by wiring. This system can be integrated into building control systems. The voltage drop in the control line wiring limits its length. Therefore, the maximum distance is limited by the number of control gears connected. The latter establishes the current per line and the cable diameter used.
Touch Control Push Button (analogue but can be connected to digital systems)
Touch Control is a system that enables the simple and economic dimming of luminous flux. It uses the mains voltage as a control signal, applying it with a standard push button on a control line, without any need for specific controllers.
The Touch Control system enables you to carry out the basic functions of a regulation system with a power-free pushbutton. Depending on how long the button is pressed it is possible to switch the light on or off or dim it. Switching the light on or off is done by short, sharp pressing or “click”. If the button is pressed for a long time it is possible to dim the luminous flux between the maximum and minimum levels alternately.
This is a unidirectional interface, i.e. information flows in one direction. The equipment does not generate any type of feedback, so it can’t be controlled with a software. Groups have to be created by wiring. This system cannot be integrated into building control systems. The length of the wiring and the number of equipment that can be connected, are theoretically unlimited. But in, asynchronism may occur during switching on and dimming, at distances longer than 25 meters, and with a larger number of fixtures connected. Owing to its characteristics, the use of this dimming method is recommended for individual offices, small meeting rooms or bedrooms, landings and small spaces in general.
Digital dimming covers all dimming systems that transform the dimming signal into bits and controls the lighting in digital format.
DALI Regulation (digital)
As revealed by the meaning of its acronym, Digital Addressable Lighting Interface, DALI is a digital and addressable communication interface for lighting systems. This is an international standard system in accordance with IEC 62386, which ensures compatibility and interchangeability between different manufacturers’ equipment marked with the following logo: DALI controller
It is a bi-directional dimming interface with a master-slave structure. The information flows from a controller, which operates as the master, to the control gears that only operate as slaves. The latter carries out the orders or responds to the information requests received. Digital signals are transmitted over a bus or two-wire control wire. These control wires can be negatively and positively polarized, though the majority control gears are designed polarity free to make connection indifferent.
You don’t need especially shielded cables. It is possible to wire the power line and DALI bus together with a standard five-wire cable. Unlike other systems, you don’t need to create wiring groups. Therefore all the pieces of fixtures are connected in parallel to the bus. Without bearing in mind the grouping of these, simply avoiding a closed ring or loop topology. You don’t require mechanical relays to switch the lighting on or off, given that this is done orders sent along the control line. You don’t need are bus termination resistors either. Consequently, the DALI interfaces offer wiring simplicity in addition to great flexibility when it comes to designing the lighting installation.
The maximum voltage drop along the control line must not exceed 2V with the maximum bus current of 250mA. Therefore, the maximum wiring distance allowed depends on the cable cross-section, but it must never exceed 300m in any case.
After wiring, the DALI lighting system is configured with the software. You can create up to 16 different scenarios, addressing the equipment individually up to a maximum of 64 addresses. This can be made with groups up to a maximum of 16, or simultaneously by means of a “broadcast” order. You can change the configuration at any time without any need for re-wiring.
The DALI system has a logarithmic regulation curve adjusted to human eye sensitivity, defined in the international standard, IEC 62386. The possible regulation range is set at from 0.1% to 100%. The driver manufacturer determines the minimum.
With the software, you can change the “fade rate”. “Fade rate” is the time needed to go from one light level to another(fade time) and the speed of the change.
The DALI system lies in the fringe between the complex and costly but powerful ones; control systems for buildings that offer total functionality and the most simple and economic regulation systems, for example, the 1-10V one.
You can use this interface in simple applications independently, to control a luminaire or a small room. You can also use it in high-level applications such as being integrated by gateways into building smart control systems.
These are the most common systems you can use to dim LED. There are a lot of different dimming systems for different driver manufacturers. I can’t cover all of those in a single blog post. I will be writing a different post about wireless dimming options.