Optoelectronics
The complexities of light flickering and LED power supply designs
By Shoubert Makanoeich from LTF Technology I A linear representation of the Visible Light Spectrum
n simple terms, visible light is a form of energy that we can perceive with our eyes. Visible light refers to the particle-like energy that appears in the electromagnetic radiation spectrum between the range of 380-700 nm (nanometres) and is detected by the human eye. Light is essential for well-being as it affects sleep patterns, vitamin D levels, mood, and more.
Flicker can be defined as the irregular rapid changes in the amplitude or intensity of light over a short duration of time (frequency), which may or may not be perceived by the human eye. Flickers occurring at frequencies below 100 Hz are referred to as visible flicker, while higher frequency flickers are called invisible flicker. Opinions differ regarding the frequency at which flicker becomes invisible. For the purposes of this paper, we will mention that flickers above 100-120 Hz are not easily visible but can still be sensed depending on the background and individual perception. Based on available studies and my personal experience working in the lighting industry for the past 20 years, both visible and invisible flickers have been associated with some health effects. Research indicates that the flicker of fluorescent light causes high rates of workplace headaches and eyestrain, and there is a correlation between these symptoms.(1)
With LED lighting being the
dominant technology in various applications, studying the flicker effects of LEDs has become even more important. Earlier studies conducted by Arnold Wilkins(2)
of the University of Essex
found that working under fluorescent lighting could be a health hazard. The study revealed that office workers were half as likely, on average, to experience headaches under non- flickering lights. Since LED flickering is even more intense, with the light dimming by 100 per cent instead of the approximately 35 per cent of fluorescent lamps, there is a possibility that LEDs could be even more likely to cause headaches.
Some common symptoms of lighting flicker include: disrupted circadian rhythms and sleep patterns, especially at certain frequencies; fatigue and eye strain, negatively impacting productivity, and well-being;
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potential health concerns, including triggers for adverse physiological reactions such as migraines or even seizures for individuals with hypersensitivity over photosensitive conditions.
The flicker performance of LED lighting is directly influenced by the design quality and performance of its power supply (LED driver), as well as dimmer control devices involved and the compatibility of these two essential components. The industry has witnessed numerous excellent LED driver designs and topologies. However, LTF Technology has for many years been manufacturing cost-effective, fully dimmable and customisable LED drivers that are extremely reliable and offer high power density, compatibility with a wide range of dimmers, and flicker-free high-performance. Designing an isolated LED driver equipped with a high-power-factor quasi-resonant flyback converter and applying constant- current sensing regulation methods will generate a sinusoidal current waveform at the input source and provide a stable DC output current on the primary side. By eliminating the need for an optocoupler or other means to cross the isolation barrier for feedback purposes, we not only reduce the driver’s size but also enhance its safety and reliability. The process of fine-tuning the circuit addresses factors inherent in the control method that affect the shape of the electrical current. LED loads require specific currents at the right voltage, which depends on the LED array configuration and power rating. LED arrays can be configured as constant voltage loads or constant current loads. Consequently, LTF Technology has developed the DA series for 120VAC input, the DS series for 120 VAC to 277 VAC input LED drivers with power ratings
Components in Electronics Figure 1: Demonstration of input voltage and output current.
Figure 2: Demonstration of input voltage and output current with a forward phase Triac dimmer.
www.cieonline.co.uk
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