PWM Dimming vs Analog Dimming: How the LED Current Is Actually Controlled

Every dimmable LED driver changes brightness by adjusting the current through the LEDs, but there are two fundamentally different ways to do it. Analog (or amplitude) dimming lowers the DC current continuously, so an LED that normally runs at 1A runs at 0.1A when dimmed. Pulse-width modulation (PWM) dimming switches the LED current fully on and off very rapidly, varying the fraction of time it spends on. The distinction sounds technical, but it determines color stability, flicker performance, and which applications each method suits — and it explains why quality dimmable drivers offer PWM rather than analog.

Analog dimming is the simpler idea. Lower the current, the LED produces less light. It works without any switching at the LED, which means no high-frequency component and no theoretical flicker risk. But it has a real optical drawback: LED color temperature shifts with current. An LED driven below its rated current changes its junction temperature slightly, and the phosphor's output spectrum shifts with it. A warm-white LED at 100 percent current may be 2700K; at 10 percent current it can drift toward 2500K or lower. In a living room this is rarely noticed; in a television studio, a retail display, or a color-critical office, it is objectionable. Analog dimming also tends to be nonlinear at the bottom of the range, and the driver's control loop must be stable at every current setting.

PWM dimming takes the opposite approach. The LED current switches between the rated value (typically the full 350mA, 500mA, or 1A) and zero, at a frequency above the visible flicker range. The average current — and therefore the average light output — is set by the duty cycle: a 50 percent duty cycle at 1A gives the same average current as 500mA in analog dimming. Because the LED always operates at its rated current when on, its junction temperature and spectrum stay constant across the entire dimming range. Color temperature is identical at 100 percent and 1 percent; this is why tunable and color-critical lighting systems use PWM.

The critical design parameter is the switching frequency. Below about 100Hz, the switching itself becomes visible as flicker, and moving objects appear strobed. Above the visible flicker range — roughly 200Hz and up — the human eye integrates the flashes into a steady brightness. But there is a second constraint: photography. Rolling-shutter cameras see light modulation above 1kHz as banding or rolling bars on the video. A driver used in a studio, in a retail window filmed by customers' phones, or in a stage setting needs a PWM frequency high enough to avoid camera interaction — typically above 10kHz, and often 20 to 30kHz. Premium dimmable drivers use high-frequency PWM (above the audible range as well) so neither eye nor camera nor microphone sees the switching.

The trade-offs sit in the driver design. PWM requires a switching stage at the LED output, which adds circuitry and means the output current is a square wave rather than smooth DC. The output filter must remove the switching component while passing the dimming frequency; get the balance wrong and you get visible ripple on the light. Analog dimming avoids this switching stage entirely but sacrifices color stability. High-end drivers offer both: analog dimming for the coarse range and PWM for fine dimming at low levels, or a hybrid mode that switches between the methods based on dim level. A driver that offers PWM at a frequency above 20kHz is, in effect, flicker-free by the standards that matter.

For a buyer, the questions are concrete. Does the dimmed light need consistent color across the range? Ask whether the driver uses PWM. Is the installation filmed or photographed? Ask the PWM frequency and confirm it is above 20kHz. Is low-level dimming expected below 5 percent? Check the datasheet's minimum dimming level and whether color shift is specified. Non-dimmable drivers sidestep the entire question — at full output, color and flicker are set by the design, not by a dimming method. But where dimming is required, understanding PWM versus analog tells the buyer which driver will behave on camera and which will not.