What is Flicker and How Can You Avoid It?
What is flicker?
Picture this: you open the camera of your phone to take a video under artificial indoor lighting. When shooting, you can see horizonal or vertical dark stripes rolling regularly on the screen. Worse, the screen might keep flickring. That is flicker. This means that the light source used for the video produced had obvious flicker.
All light sources connected to mains power produces flicker.
Mains power is an alternating current supply that switches between positive and negative voltages at a frequency of 50-60 Hz in a sinusoidal waveform. This means that all light sources connected to the mains are switched on and off periodically.
It seems though we do not see flickering light sources in our daily lives.
The degree of flicker of a light source can be quantified by percent flicker and flicker frequency. The percent flicker (stroboscopic deepth) is the ratio of the differnce between the maximum and minimun luminance and the sum of them in a cyclical fluctuation, which is defined as: Flicker Percent (%) = 100 × (Lmax – Lmin) / (Lmax + Lmin). The flicker frequency is the number of flicker cycles of the light source per second.
Incandescent bulb, as one of the typical traditional light source, due to its light-emitting principle (heat energy directly converted into light). When the voltage becomes 0V, there remains leftover residual heat on the filament, maintaining its glow. Therefore, the percent flicker of an incandescent bulb is about 15%. Even if the current increases or decreases and changes in direction at a frequency of 50-60 Hz, it still appears as a light source of constant brightness due to the low flicker percentage.
The response time of LED is quite short, only about 1 microsecond second. LED is a unidirectional conduction diode, and it is driven by LED for AC and DC conversion. Unfortunately, the DC output of an ordinary drive will contain some periodically changing ripples. One of the important characteristics of LED is that the brightness will change according to the change of the input. Since the response speed of the LED is too fast, which is in the millisecond range, the ripple carried by the output of the ordinary driver is enough to bring the periodic change of the brightness. This is the main reason why ordinary LED lights flicker.
The human eye usually can only observe flicker below 100 Hz, so the flicker of the LED light source is still not perceptible. But at this speed, the flicker of the LED light source is still much stronger than that of an incandescent lamp.
The health risks of flicker
Although the ordinary flicker cannot be detected by the human eye, its health risks cannot be ignored. Research suggests that this invisible flicker has adverse effects on human health, such as eye fatigue, dizziness, headaches, and many other detrimental symptoms. Moreover, this fast flashing light source is incompatible with the natural state of the human absorption of stable natural light.
Can the flicker of LED light source be avoided?
The rule is simple. Studies show that ultra high flicker (＞3125 Hz) has negative influence on both shutters and human eyes. So either reducing the percent flicker or increasing the flicker frequency of the LED light source will eliminate the flicker.
Professional LED power supply provides flicker free LED light
LEDs can only be driven in DC systems. In theory, if the LED is given a stable and constant current and voltage, the LED can provide stable brightness. Therefore, whether the LED light source flickers is determined by the power supply used.
As mentioned above, the simplest transformer only converts the AC signal into a DC signal by simply switching the polarity of current / voltage. The professional LED power supply smoothens the current / voltage at the same time and produces a constant current / voltage.
For LED bulbs, the power supply is built into the bulb, so it is particularly important to choose a bulb with a flicker-free statement. Yuji’s flicker-free LED bulb series uses a professional flicker-free power supply with a percent flicker of less than 5%. This provides a comfortable working and resting environment, suitable for any commercial lighting, home lighting, and photography and film studio lighting.
Flicker is not actually determined by the LED strip but by the power supply source. Using a professional constant current / constant voltage power supply designed for LED is essential.
Yuji flicker-free LED power supply provides 120W power for most single color, bi-color, RGB and RGBW LED strips, and is also suitable for all Yuji Lighting™ LED strip products.
This constant voltage power supply provides 2% voltage accuracy, meeting the flicker-free requirements of most applications. This is compatible with the DC side dimmer and provides smooth, flicker-free dimming for single color, bi-color, RGB and RGB + white light LED strips throughout PWM dimming.
PWM dimming and its flicker free solution
For applications that require dimming LED light sources, a common LED dimming method is pulse-width modulation (PWM). PWM is the adjustment brightness of the LED by changing the time ratio of the LED between 100% and 0% brightness. LED light sources that use PWM dimming essentially flicker at higher frequencies. But when the flicker frequency reaches more than 25000Hz, it has far exceeded the human subconscious perception, and it is enough to eliminate the effect of flicker in photography applications. At this rate, it can be considered that the LED is flicker-free.