Leading Edge Dimmer
A dimmer type that cuts the leading (front) edge of each AC wave. Originally designed for incandescent and halogen — can cause buzzing and flicker with LEDs.
Leading edge dimmers were the standard for decades because they're cheap to manufacture and work perfectly with incandescent and halogen bulbs. They cut the front of each AC wave cycle, effectively reducing the total power delivered to the bulb. With a resistive load like an incandescent filament, this produces smooth, predictable dimming.
The problem is that LEDs aren't resistive loads — they're electronic devices with drivers that expect clean power. When a leading edge dimmer chops the front of the wave, many LED drivers can't process the abrupt voltage spike that follows. The result is flickering, buzzing, limited dimming range (won't go below 30-40%), or the LED turning off entirely at low dim levels.
Some modern LED bulbs are specifically designed to work with leading edge dimmers — check the manufacturer's compatibility list. But if you're installing new dimmers or troubleshooting existing dimming problems with LEDs, replacing a leading edge with a trailing edge dimmer is the most reliable fix.
Specifications
| Also called | Forward phase, TRIAC (sometimes) |
| Best for | Incandescent, halogen, MLV |
| LED compatible? | Sometimes — check dimmer/bulb compatibility |
Related Terms
- Trailing Edge Dimmer
A dimmer type that cuts the trailing end of each AC wave cycle. Smooth, quiet, and compatible with most LED bulbs — the recommended type for LED dimming.
- TRIAC Dimmer
The most common phase-cut dimmer circuit, found in most residential dimmers. Works by chopping the AC waveform. Some TRIAC dimmers work with LEDs, many don't.
- Flicker
Rapid, repeated changes in light output. Can be visible (strobe effect) or invisible but still cause headaches. Usually caused by incompatible dimmers or poor LED drivers.