PWM dimming controls LED brightness by rapidly switching the power supply on and off at a fixed frequency, typically ranging from 200 Hz to several kHz. The average current through the LED – and thus its perceived brightness – is determined by the duty cycle, i.e., the ratio of on‑time to total cycle time. A 100% duty cycle means full brightness, while 10% produces a dim 10% output. The key advantage of PWM is its exceptional linearity and color stability: because the LED operates at its rated forward current during the on‑phase, the color temperature remains constant across all dimming levels. This makes PWM ideal for applications where color fidelity is critical, such as retail displays, museums, and photography studios.
However, a critical parameter is the switching frequency. If the frequency falls below about 200 Hz, the human eye can perceive flicker, leading to visual fatigue, headaches, or even triggering photosensitive epilepsy in susceptible individuals. Professional lighting fixtures typically use frequencies above 1 kHz – often 20 kHz or higher – to eliminate visible flicker entirely. For example, in a high‑end office renovation, the design team specified PWM drivers with a 25 kHz switching frequency, ensuring that even under high‑speed video recording, no banding or flicker artifacts appeared. The main limitation of PWM is that it can introduce electromagnetic interference (EMI) at high frequencies, requiring careful shielding and layout. Nonetheless, for most LED lighting applications, PWM remains the most widely adopted dimming method due to its cost‑effectiveness and superior performance.
