Over time, we found it easiest to explain dimming by AC and DC control approaches. So, we shall discuss the relevant details with this approach. Before the start, let's warm up with some basic concepts.
Dimmable Fixtures in a Non-Dimmable Circuit
Although people would find non-dimmable lamps somewhat reduce the brightness intensity as the input power reduces before the lights go off, clearly, this is not what we mean by dimming. Dimmable LED fixtures can smoothly manipulate the brightness intensity as users purposely dim the lights.
Let's consider the rated constant current of a dimmable LED driver as its maximum output current to the light; without a dimmer, the driver outputs at its max. So, we can use dimmable LED fixtures in a non-dimmable circuit, but the reverse is not valid.
LED Driver Classifications
When purchasing a new printer, we need to install the corresponding driver software for the specific model. Similarly, LED lights have different input requirements and thus, require specific LED drivers. If the driver's output voltage doesn't match, the LED lights won't function properly. Before we can select a driver for a LED light, as in the case of a LED recessed downlight, we shall have some understanding of LED drivers.
Judging by the output, most LED drivers have constant current outputs, which are different from a standard laptop power supply. The LED driver usually has a rated constant current (mA) in a specific voltage range. For example, Meanwell APC-16-350 is a 16.8W non-dimmable LED driver with a constant current output of 350mA in the 12Vdc – 48Vdc range, whereas APC-16-700 is a 16.8W non-dimmable LED driver with a constant current output of 700mA in the 9Vdc - 24Vdc range.
While most LED drivers have constant current output, some have constant voltage output (12Vdc / 24Vdc / 48Vdc) that operate on PWM signal (right), and some have a constant power rating. More advanced LED drivers feature a dual-operation mode that can work as a constant current or a constant voltage driver depending on the loading condition. But in most cases, we shall be dealing with constant current LED drivers and focus on dimmable drivers that work on the Constant Current Reduction principle, meaning that the output current and the brightness intensity change along a dimming curve. See more on Dimmable LED Driver Selection.
In daily product selection, we’d be dealing with LED lights with integral drivers (e.g., a dimmable MR16 lamp) or external drivers. Since the LED driver dictates the dimming feature, we must specify a dimmable LED lamp or track light at the outset if it’s what we want. On the other hand, for LED downlights and light fixtures that usually have an external LED driver, we can replace a non-dimmable driver with a dimmable one. Other than that, prospects shall explore more about inrush current discussion and flicker-free options if these options are relevant to their applications.
AC (Phase-cut) Dimming
As the name implies, AC dimming is about manipulating the AC input power from the live wire to dimmable LED fixtures. Since electrical systems operate in the form of AC sinusoid waveform (110 / 220Vac), we can manipulate the input power by chopping part of the sine wave. The more we chop, the subsequent lights receive less input energy. Naturally, we can further identify two ways to chop the AC waveform: Leading-edge (rising edge) and Trailing-edge (falling edge) phase-cut approach.
Although the two mutually exclusive methodologies work with incandescent and halogen lamps, the leading-edge approach has proven to cause different issues with LED lights or capacitive loads. For LED dimming, it’s agreed to use the trailing-edge phase-cut dimming methodology. Our Gen 2 phase dimmers feature a “Universal” control technology that can automatically provide leading or trailing-edge phase-cut signal subject to the load’s response. However, as trailing-edge is becoming more popular with LED drivers and the trend to replace incandescent or halogen lamps with LED lights is irreversible, we focus on trailing-edge output in our latter dimming cores instead.
TRIAC Dimmer vs. Trailing-edge Dimmer
To set the stage for our discussion, let’s make a simple classification of the key terms, such as phase-cut dimmers, TRIAC dimmers, and trailing-edge LED dimmers. Simply put, TRIAC dimmers are leading-edge dimmers. Both TRIAC dimmers and trailing-edge LED dimmers are phase-cut dimmers that manipulate the input power to the LED lights by chopping the sinusoid waveform of the AC Mains.
TRIAC dimmers have been around since the incandescent and halogen lights era. Given its long history, people often consider TRIAC dimmers as the "light dimmer." The TRIAC dimmer replies on a single TRIAC IC (in the yellow box) and a few passive components to perform leading-edge phase control common in small home appliances, such as hairdryers and toasters.
If we open a TRIAC dimmer, we'll immediately recognize the large heat sink attached to the TRIAC IC. The large heatsink is responsible for the heat dissipation as the TRIAC IC reduces the energy into the lights. From a product perspective, this large heat sink posts a massive limitation in the size of the TRIAC Dimmer. Customer may visualize the size difference of a TRIAC dimmer and our 450W trailing-edge LED dimmer module!
Besides that, Electricians can judge whether a dimmer is suitable for LED lighting by the dimmer's minimum load requirement; for example, if a dimmer switch has a rated power of 50W – 400W (even 1000W), it is likely designed for incandescent and halogen lights. Note a typical halogen bulb is around 50W or 100W.
The issue with TRAIC dimmer with LED dimming is that LED lights can operate at shallow current levels, leading to potential conflicts with the TRIAC IC’s Holding Current, which is crucial for the semiconductor device to sustain its operations. If the TRIAC IC can’t maintain its function, flickering occurs. This parameter varies greatly across many component suppliers, and the amount of current required to draw from the TRIAC IC is subject to the fine production details. Hence, this crucial parameter dependence introduces a critical potential fault for consistent dimming performance and becomes a project nightmare.
Other than that, the severe inrush current and the repetitive current spikes with TRIAC dimmers that weaken the product lifespan are also valid causes for not using them with LED dimming. We met some Electricians who would need to replace the TRIAC dimmers regularly. Trailing-edge dimmers have the advantage of avoiding repetitive current spikes as found with leading-edge dimmers and processing other digital control advantages. Thus, trailing-edge LED dimmers are preferred to the traditional light dimmers and provide robustness in LED dimming.
On the other hand, DC dimming approach requires additional linkage (isolated low voltage) from a control unit to the dimmable fixtures, though the connection can be wired or wireless. The dimmable drivers adjust the brightness intensity upon receiving the control signal or command.
The control signal can be analog, as in the case of 0/1-10V, or proprietary digital commands that consist of a device ID and instruction. The transmit and receive-ends often operate on a pre-defined communication protocol; hence, specific devices are required.
In the case of Smart Bulbs, the linkage between the control unit (i.e., mobile device control by application software) and the bulbs is a wireless connection. At the moment, Bluetooth (BLE), Wi-Fi, and a few others are the common wireless communication protocols. Since these fixtures / lamps embed a wireless module (the RF Tx / Rx block and command decode unit), fixture design has some limitations. In our Hybrid Dynamic Lighting control mode, we use a BLE or Wi-Fi module with 0-10V output to connect our DZ1G300TUNE controller to achieve wireless / intelligent control purposes.