Flicker Research

Since 2009, DOE has conducted research on the visual phenomenon commonly known as flicker. More formally called temporal light modulation (TLM), it is defined as rapid variation in light source intensity, which can cause visual effects ranging from uncomfortable or distracting to harmful or (rarely) dangerous. This has become a more serious consideration in the age of solid-state lighting (SSL) because LEDs and OLEDs are devices with little thermal or phosphor persistence, so there is a very rapid on or off response of the LED from the current delivered by the driver/dimmer electronics. Drivers for these devices can deliver current through an infinite variety of time-based waveforms, varying in shape, modulation depth, duty cycle, and frequency.

In the last 20 years, research and observation have shown us that if there is relative movement between the eye, head, lighted object, and the light source, TLM can be visible even at high frequencies of 1000, 2000, 6000 Hz, or even higher. In fact, under very dark conditions, some individuals can accurately identify the modulating source from a steady output source up to 11,000 Hz. It has also become clear that there is a wide individual variation in responses. Some can see “flicker” clearly under conditions where less sensitive individuals will see none at all. Are these sensitive observers the same people susceptible to migraines or other conditions? There is no conclusive answer from the neurology community as yet.

There are three established visual responses to TLM:

  • Direct flicker is the perception of visual unsteadiness induced by a light stimulus where the luminance fluctuates with time, for a stationary observer with a fixed gaze.
  • The stroboscopic effect is indirectly perceived and requires the movement of an object within the visual field, illuminated by the modulating light. As the object moves, its luminance varies, creating a discontinuous visual image of the object (see Figure 1 below).
  • The phantom array effect involves the interaction of the observer’s visual saccade (rapid movement of the eye between fixation points) relative to the modulating light source, or an object lighted by it, and can produce a discrete set of dots or dashes or parallel edges on the retina (see Figure 2 below).

The scientific understanding of TLM is growing and evolving, and DOE provides analysis and technical support for various industry organizations working to develop improved test and measurement procedures to better characterize flicker. In addition, DOE research conducted by Pacific Northwest National Laboratory is advancing the science by accelerating our understanding of TLM waveforms that elicit visible responses, improving metrics that predict these responses from normal and sensitive populations, and encouraging the adoption of predictive metrics and appropriate test methods related to TLM.