Figure 1. Communal Bridge with MOONS’ LED drivers, Russia
Introduction
There are two types of flickering with lights – visible flicker and invisible flicker. Obviously, visible flicker is the one our eyes can see, which is when the light output from a given source changes rapidly. It is considered that anything below a frequency of 100Hz can be seen. Invisible flicker is not consciously perceived but may still have biological or even health effects on humans
Where does flicker come from?
To better understand flickering in lights, consider the theatrical effect known as strobe lighting. This is a deliberate flicker effect that delivers light at certain frequencies, causing the brain to interpret moving objects as if they were in slow motion. These specified frequencies are generally just a few flashes per second, but they are very close to frequencies that cause epileptic seizures.
Unintentional flickering in lighting equipment can be traced back to our power companies that designed electricity flow to use alternating current (AC) as opposed to direct current (DC). With AC power, the sine wave will peak both positively and negatively. This leaves it susceptible to being in a range that will cause flickering, or sometimes an audible hum.
How to solve LED flickering issues?
LED flickering can be tied back to the driver component within the lamp. The essential purpose of the LED driver design is to rely on a simple circuit to control output current, but without altering the frequency, the LED becomes likely to show visible flicker. However, this can be fixed by using constant current drivers, which remove the peaks of the sine wave.
The best way to avoid flicker is to use LED drivers:
• Two-stage, high frequency LED drivers such as MOONS’ CP series LED drivers;
• LED drivers which dim using either DC or Constant Current Reduction
• LED drivers which dim using Pulse Amplitude Modulation (PAM)
MOONS’ uses a hybrid approach to dimming in which it uses the attributes of both PWM and Amplitude Dimming to create a solution that is smoother, deeper, and has a low risk of flicker throughout the dimming range. PWM is used when lower light levels are needed and amplitude dimming is used at higher levels of light output. Figure 5 shows the detail about this dimming strategy.
Figure 2. Hybrid Approach to Dimming
From the picture below you can see MOONS’ LED drivers’ performance in the flick. That is tested by UL authority. The picture shows flicker percent vs. flicker frequency of the MOONS’ intelligent LED drivers. At different dimming levels, all frequency components in the light output are measured. These frequency components are plotted in a graph (the dots in figure 3). In the green area, there is no observable effect. In the faint yellow area, there is low risk and no dot in the pink area.
Figure 3. Flicker percent vs. Flicker frequency
