Solving The Flicker Problem

Research into solving the flickering light problem from an electrical engineering perspective.

There are a few approaches to reduce perceived flicker. Some discussion about the methods:

In AC LED lighting, one common issue is the flicker index of a light. Flicker index is how much the light gets brighter and dimmer over time. This problem is well understood by video recording engineers. Most common household LED lights get brighter and dimmer 120 times per second, exactly twice the frequency of the AC power grid, which is 60 times per second. Some of these lights have a big difference between the brightest and dimmest (a high flicker index), some have a much smaller flicker index. This is often because while the power supply in a light is trying to provide a steady amount of electricity to the LED (and thus a steady amount of light), it is difficult to convert AC power to perfectly stable DC power. It is possible but doing it efficiently, inexpensively, and in a small package is a technical challenge.

In DC LED lighting, one common issue is the frequency that the light is flickering at. Dimming LED lighting is often accomplished by using a technique called pulse width modulation (PWM). Instead of actually dimming the light, the light is turned fully on and off very quickly. If, for instance, the light is turned on and off in equal measure, the light will appear to be at 1/2 brightness. If you turn the light on and off every second, no one’s eyes will be fooled into thinking it is 1/2 brightness. If you turn the light on and off 1,000 times per second, most people’s eyes will be fooled. This limit of the human eye is referred to as the flicker fusion frequency. Unfortunately, there are some complexities that is lost on many lighting specialists. Many DC lighting systems flicker at 200 Hz or 500 Hz. The common, incorrect belief is that “no one can see faster than about 30 frames per second” but we can! Another issue is that even if the lights are flickering very rapidly, when a person turns their head quickly, this flicker can be very easily seen as a series of dashes streaming across their vision; this is called the phantom array effect. This can be a dangerous distraction in a nighttime driving environment!


Articles about flicker in AC LED lighting:

Articles about flicker in DC LED lighting: