To control mains-voltage or high-power DC LED fixtures with a microcontroller, you never switch the mains directly from the board. Instead, an LED Arduino lighting circuit uses the microcontroller's PWM (Pulse Width Modulation) pins to command a 0-10V dimming module or an AC phase-cut interface. That interface then drives a compatible constant-current LED power supply. Getting this right requires matching the driver's power factor, respecting dimmer minimum loads, and filtering PWM ripple to prevent visible flicker.
Sizing the LED Load: Efficacy, Inrush, and Power Factor
Before writing a single line of code, you must size the constant-current driver. Modern commercial LED panels and high-bay fixtures are vastly more efficient than legacy lighting, but they introduce complex electrical behaviors like high inrush currents and low power factors at partial loads. According to the U.S. Department of Energy Solid-State Lighting guidelines, LED efficacy continues to climb, meaning you need less wattage to achieve target lumen outputs, which directly impacts your breaker sizing.
| Fixture Type | Nominal Watts | Output Lumens | Efficacy (lm/W) | Driver PF (Full Load) | Inrush Multiplier |
|---|---|---|---|---|---|
| 2x2 Troffer Panel | 30W | 4,200 lm | 140 lm/W | 0.95 | 150x (45A peak) |
| High-Bay UFO | 150W | 21,000 lm | 140 lm/W | 0.98 | 250x (375A peak) |
| Architectural Strip | 15W | 1,500 lm | 100 lm/W | 0.85 | 80x (12A peak) |
| Retrofit Downlight | 9W | 800 lm | 88 lm/W | 0.70 | 50x (4.5A peak) |
Dimmer Selection and Arduino PWM Interfacing
When dimming LEDs on an AC circuit, the phase-cut method matters immensely. Legacy incandescent dimmers use Leading Edge (TRIAC) phase-cutting, which chops the beginning of the AC sine wave. LEDs require Trailing Edge (ELV) dimming, which chops the end of the sine wave. Trailing edge dimmers use MOSFETs or IGBTs, providing a softer turn-off that prevents the voltage spikes that destroy LED driver input capacitors.
Which dimmer and driver for your fixture count?
- 1 to 4 Fixtures (Under 60W Total): Use an Arduino-controlled AC phase-cut module (like the RobotDyn 3.3V/5V AC Light Dimmer). This module sits between the mains and the fixture's internal driver. Crucial check: Ensure the total connected wattage exceeds the dimmer's minimum load. A standard Lutron Maestro ELV dimmer requires a 15W minimum load; if your Arduino controls a single 9W LED bulb, the circuit will strobe or fail to turn off completely.
- 5+ Fixtures or Commercial Panels (Over 60W): Abandon AC phase-cutting. Use an Arduino PWM-to-0-10V sink/source module to command a commercial constant-current driver like the Mean Well HLG-150H. The 0-10V standard (defined by the NEMA SSL 7A standard) isolates your low-voltage microcontroller from the mains entirely and scales perfectly to daisy-chained multi-fixture runs.
Eliminating Flicker: Frequency Matching and Zero-Crossing
The most common failure mode in an LED Arduino project is visible flicker or a high-pitched whine from the driver. This happens because of a mismatch between the microcontroller's PWM frequency and the LED driver's internal control loop.
By default, most Arduino Uno and Nano pins output a PWM frequency of roughly 490Hz (pins 5 and 6 run at 980Hz). If you feed this raw 490Hz square wave directly into the analog input of a 0-10V LED driver module, the driver's internal comparator reads the rapid voltage swings as a command to constantly ramp the current up and down. This creates a 120Hz beat-frequency flicker that is highly visible on camera and fatiguing to the human eye.
The Fix for 0-10V Dimming:
You must smooth the PWM signal into a flat DC voltage before it reaches the driver. Build a simple low-pass RC (Resistor-Capacitor) filter on your breadboard or PCB. Place a 1kΩ resistor in series with the Arduino PWM pin, and connect a 10µF electrolytic capacitor from the other side of the resistor to ground. According to Arduino analog output documentation, this filter will smooth the 490Hz ripple into a clean, steady DC voltage that the 0-10V driver reads as a stable dimming command.
The Fix for AC Phase-Cutting:
If you are using an AC dimmer module, you cannot use analogWrite(). You must use a hardware zero-cross detector (like the H11AA1 optocoupler) wired to an Arduino hardware interrupt pin. The code must calculate the exact microsecond delay from the zero-cross point before triggering the TRIAC/MOSFET gate. If your timing is off by even 50 microseconds, the AC waveform will be asymmetrical, causing the LED to flicker at 60Hz.
Thermal Constraints and Enclosure Derating
High-power LED drivers are highly efficient, but they are not perfect. A premium Mean Well HLG-150H driver operates at roughly 93% efficiency at full load. That remaining 7% of the 150W input (10.5W) is dissipated as heat. When you mount this driver inside an enclosure to hide the wiring from your Arduino control circuit, that heat has nowhere to go.
If you use a standard NEMA 1 (indoor, non-ventilated) plastic enclosure, the internal ambient temperature will quickly rise. LED drivers feature internal thermal protection that will throttle the output current (dimming the lights) or shut down completely if the internal case temperature exceeds 85°C to 90°C.
1. Plastic Enclosures: Derate the driver's maximum load by 20%. If you are using a 150W driver in a sealed plastic box, limit your connected LED load to 120W.
2. Metal Enclosures: Aluminum acts as a passive heatsink. You can typically run the driver at 100% load, provided the enclosure has at least 20 square inches of surface area per 10W of dissipated heat.
3. Ventilation: If the enclosure must be plastic and fully loaded, install passive louvered vents at the bottom and top of the box to create a natural convection chimney, pulling cool air over the driver's heatsink fins.
By respecting the inrush math, filtering your PWM signals, and providing adequate thermal headroom, your LED Arduino lighting circuit will deliver smooth, flicker-free dimming that lasts for tens of thousands of hours.
