PWM Dimming
A dimming method that rapidly switches LEDs on and off thousands of times per second. The ratio of on-time to off-time controls perceived brightness.
PWM dimming works by rapidly switching the LED fully on and fully off — not by reducing the voltage. At 50% brightness, the LED is on half the time and off half the time. Because this switching happens thousands of times per second (typically 1-20 kHz), your eye perceives it as a steady dimmer light rather than a strobe.
The main advantage of PWM over analog (voltage reduction) dimming is color consistency. When you reduce voltage to an LED, its color temperature shifts — warm whites get even warmer, and some LEDs develop an unpleasant greenish tint at low levels. PWM avoids this because the LED is always running at full voltage when it's on; only the on-time changes.
The catch is frequency. Below about 1 kHz, some people can perceive the switching as flicker, especially in peripheral vision. This is also why LED tail lights on cars can appear to strobe when you move your eyes quickly — the camera in your phone picks it up even more easily. High-quality LED drivers use PWM frequencies of 10 kHz or above, which is imperceptible to everyone.
Specifications
| Frequency | Typically 1-20 kHz |
| Advantage | Consistent color at all dim levels |
| Disadvantage | Can cause visible flicker if frequency is low |
Related Terms
- 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.
- Dimming Range
The brightness span a dimmer can achieve — typically expressed as a percentage (e.g., 5%-100%). A wider range means dimming to a lower level without flickering or shutting off.
- LED Driver
A power supply that regulates current to LEDs, preventing flickering and enabling dimming. Every LED has one — either built into the bulb or as an external unit.