1.What is strobe？
First introduce the unit of hertz (stroboscopic), Hz stands for frequency. Frequency refers to the number of repetitions of 1 second when electric pulses, alternating current waveforms, electromagnetic waves, sound waves, and mechanical vibration cycles are cycled.So “stroboscopic” as its name implies is a regular cyclic flashing fluctuation of the light source within 1 second due to various reasons.Most of us can obviously perceive strobe below 60Hz, which is why the TV sets the refresh rate above 60Hz (video images are composed of a group of consecutive frames of pictures, follow the principle of flipping the book Similarly, the faster the movement, the more consistent the movement).
When the frequency of the strobe reaches a certain level, the human eye will not perceive the flicker, and will regard the light source as a continuous light source.Since household electricity is almost always alternating current 50 / 60Hz, any light bulb will have stroboscopic phenomenon. For the old-fashioned incandescent lamp, the strobe will not be obvious due to the principle of light emission.
2.What are the health hazards of strobe?
Strobes within the visually perceptible range may cause migraines, headaches, dizziness, eye fatigue, blurred vision, etc.
Strobe is also a type of light pollution. Similar light pollution includes glare and diffusion. Therefore, the choice of light source will also determine the mental state of our daily life, and also affect our health.
Some people are rumored that the camera shooting LED lights have stripes. This means that the LED lights have strobes. This method is wrong because the camera and the LED lights have a difference frequency. It is obviously a bit stupid to use this method to detect the quality of the LED lights.
3.Why the LED lights will flicker？
In addition to LED chips, LED lights leave a pile of circuit boards and originals. There are many ways to classify and name LEDs, and there is basically no unified standard.
We use a simple but convenient way to divide the two: drive components and dimming components (or circuit).
The driving component is a general term for the various components that provide the appropriate current for the LED chip. It includes functions such as AC to DC conversion, voltage reduction, rectification and filtering, constant current, and constant voltage.
The dimming component is a component that adjusts the brightness of the LED chip. In fact, in many cases, the dimming component is included in the driving component. For convenience, we will separate it.
In the workshop, “DC (direct current) dimming” and “PWM dimming” are often used to distinguish the dimming method, but I am a little confused, because except for a few “AC LED”, most of the home LED bulbs are originally DC powered. .
So I think what they want to say is “CCR (constant current) dimming”. In order not to cause confusion, we will still call it “DC dimming” below.
The strobe of LED is largely not a problem of the LED chip itself, but from the driving and dimming components. The common causes of strobe are:
First, poor quality drive components cannot reduce the “voltage and current output ripples” generated during the process of “changing from AC to DC” and “from drive components to LED chips”.
Second, poor-quality dimming components are either poorly compatible or low-frequency PWM dimming is selected. It is necessary to remind everyone that LED products with dimming function have dimming components, including some “dimmable, lighting” LED bulbs and almost all “LED backlight” displays.
4.How to reduce the screen flash?
If it is the problem of the driving component, then increase the constant current component and improve the circuit design to improve the performance of adjusting the current.If it is a problem with the dimming method, change the dimming method and improve the adjustment components. Or use constant current “CCR dimming”, also known as “DC dimming”. Or increase the “PWM dimming” frequency, because the use of high-frequency drive LED lights, the proportion of strobe is small, and DC drive does not necessarily have no strobe. Or use a mixed dimming method (such as: PWM + DC), because for dimmable LED, PWM and DC dimming have their own advantages.
To sum up:
Any light source has a stroboscopic, but the degree is different. Whether the stroboscopic is perceived varies from person to person, depending on the mode, state and environment; for example, the refresh rate of LCD monitors is mostly 60 / 70hz, which seems not to give much People cause trouble.
Generally speaking, incandescent lamps, fluorescent lamps that use “electronic ballasts”, LED bulbs that use high-quality drive parts, and PWM dimming and DC dimming LED displays that have “higher driving frequency” have lower strobe , Generally does not cause problems.
Fluorescent lamps using “inductive ballasts”, LED bulbs with “inferior drive components” and LED backlights with “lower driving frequency” PWM are easy to make people feel flickering and cause discomfort.
The strobe of LEDs mainly comes from driving and dimming components. Their structure is much more complicated than incandescent and fluorescent lamps. There are still compatibility issues among various components. Big factory light bulb.
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