Flicker
When people hear the word flicker, they often think of an old fluorescent lamp blinking on and off, or a faulty light fitting that clearly needs replacing. That type of flicker is easy to identify.
However, in modern LED lighting, these variations in light output are often much more subtle and not easily perceived by the human eye. The technical term for these fluctuations is Temporal Light Modulation (TLM), which describes variations in a light source’s output over time.
Some forms of TLM are directly visible, while others only become apparent under specific conditions. For example, rotating machinery may appear to slow down, stop or break apart visually due to stroboscopic effects. Rapid eye movements can also produce phantom array effects, where multiple images of a light source are perceived across the visual field.
In other cases, the TLM may not be consciously perceived at all, yet it can still be detected by the retina and visual system, potentially influencing visual comfort, concentration and performance. This is why saying "I can't see any flicker" is not always enough to determine whether a lighting installation is free from temporal light modulations.
Not all modulation is equal
The effects of poor temporal light quality extend beyond simple visual annoyance. Depending on factors such as modulation frequency, modulation depth, waveform, exposure time, luminance and individual sensitivity, flicker and other temporal light modulations can contribute to eyestrain, headaches, distraction, reduced visual performance and, in some environments, create safety risks.
This is also why the term "flicker-free" should be used carefully. Almost all mains-powered LED luminaires exhibit some level of TLM, including many non-dimmable products. Rather than asking whether a luminaire is flicker-free, it is often more useful to understand how much modulation is present and whether it falls within accepted low-risk limits.
Evolving Industry Metrics
Today, lighting professionals assess temporal light modulation using a combination of established metrics and guidance documents. Common measures include PstLM, which quantifies short-term flicker visibility, and SVM (Stroboscopic Visibility Measure), which evaluates the visibility of stroboscopic effects. Alongside these, IEEE 1789 is widely used as a key benchmark for assessing flicker risk in lighting specifications and project requirements.
While these metrics do not capture all aspects of how people respond to temporal light modulation, the industry has clearly moved beyond treating flicker as a simple yes-or-no issue. Temporal light quality is now considered a broader design and specification factor across a wide range of projects, including office environments, education facilities and industrial settings, anywhere visual comfort, concentration, accurate motion perception or safety are important. It is particularly significant in settings such as healthcare, aged care, education and neurodiverse environments, where occupants may be more sensitive to TLM.
Beyond Photometrics
As LED technology, drivers, controls and dimming systems continue to evolve, lighting performance must be evaluated beyond photometric and colour characteristics to include how consistently and reliably light is delivered in real-world operating conditions.
Flicker, and TLM in general, are therefore essential considerations in defining overall lighting quality, alongside glare control, colour quality, visual comfort, non-visual effects and energy efficiency, forming a holistic framework for modern lighting design and specification.
Contact us today to explore how we can help design lighting solutions that go beyond what the eye can simply see, supporting greater comfort, performance and wellbeing.
