Why does the LED light flicker on the camera?

14/01/2022
led light,led lamp
Why does the LED light flicker on the camera?

"Stroboscopic effect" is a perceptible flickering effect, which usually occurs when the mobile phone is shooting towards the LED light source.
Have you ever seen a stroboscopic image when a mobile phone camera takes an LED light source, but it is normal when viewed directly with the naked eye? You can do a very simple experiment. Turn on your mobile phone camera and aim it at an LED light source. If your car has a fluorescent lamp, you can easily observe this strange phenomenon through the smart camera camera.
In fact, the flashing frequency of LED light source is undetectable to the human naked eye. Car evaluation lovers often encounter some crazy scenes: when taking pictures of cars, the car starts the fluorescent lamp, and the final shooting effect will make them very depressed. This stroboscopic effect can be simply explained as the conflict between the two lights.

What is stroboscopic effect?
If you look through the previous physics books, you will find that people usually have a tendency, which is called "visual persistence phenomenon". We can continuously perceive things. Even if they no longer appear in front of us, we can see "continuous images", rather than a set of discrete static images.

The LED light source flickers at high frequency, which is imperceptible to the naked eye. Therefore, we see that the light is on until we turn off the power completely. Similarly, video is actually a series of fast and continuous captured images, which are captured in frames per second. When we play games together, this continuous vision will deceive our brain to treat the events on the screen as a continuous fluid movement.
When the number of frames per second exceeds the LED light source frequency, the mobile phone camera shows an obvious flicker effect, which is the stroboscopic effect.
When the LED lamp is switched on and off quickly, it will flash. Whether it flashes mainly depends on the nature of the current supplied to it. Generally, the flashing frequency of LED lights is very high, which can not be directly detected by the human naked eye, or invisible to the naked eye. Therefore, people can rest assured that any visible camera flashing is actually the normal operation of lights, and the only thing that should attract attention is human blinking. However, it is a very broad statement to say that the LED lamp is always flashing during operation.
DC power supply
When the DC power supply provides power to the LED lamp, the DC power supply here is usually the battery, and the LED lamp diodes are always in the charged state. Therefore, they continuously release light energy and remain on until the circuit is disconnected. When the mobile phone camera takes pictures of LED lights powered by DC, the picture will flash continuously.

AC power supply
AC is usually provided by power supply such as wall socket. In essence, AC is turned on twice and turned off three times in a cycle. Therefore, the excited electrons consume all energy in the form of light, return to the electronic shell three times, and then excited again. Therefore, an led directly connected to the AC power supply flashes in the video.
However, it is not feasible to connect the LED lamp directly to the AC power supply, which will lead to a significant reduction in the life of the LED lamp due to the cyclic switching of the switching state. Therefore, they are connected to a regulator called a "driver", which converts AC to DC before wiring them to the lights, and the LED lights running through the driver do not flash.
Pulse width modulation
With the continuous development of transmission technology, the stroboscopic of mobile phone camera caused by LED lamp is not only completely attributed to AC or DC power supply, but the LED lamp powered by the driver will flicker. In order to reduce power consumption, the power supply can be bundled into discrete pulse current rather than continuous power source, which is the so-called pulse width modulation, which is usually used for automotive fluorescent lamps.
Can the strobe stop?
Stopping the stroboscopic effect itself is very useless. However, we are trying to eliminate the stimulating stroboscopic effect. Although eliminating the stroboscopic effect is an incredible precision task, it is easy to reduce it by adjusting the frame rate and shutter speed.
Except for the United States, AC is supplied at a frequency of 50 Hz, which means that the current changes 50 times between on and off in 1 second. The stroboscopic effect is significantly reduced by adjusting camera parameters, that is, the shutter speed and frame rate are multiples or fractions of 50.
Some LED lamps are adjusted by the driver. The flicker frequency is controlled by adjusting their switching cycle. If the flicker rate exceeds the camera frame rate, the stroboscopic effect can be effectively eliminated.
Do incandescent bulbs also flash?
Like the LED lamp, the incandescent bulb is switched on and off in AC, that is, in the off state, the filament in the incandescent bulb is not sufficiently cooled, which will not have a significant effect on the mobile phone camera. Therefore, it is impossible for us to see the incandescent bulb flashing on the mobile phone camera.