Why do LED lights flicker on the camera?

The "stroboscopic effect" is a perceptible flickering effect that typically occurs when a phone is pointed toward an LED light source to shoot.

Have you ever seen a stroboscopic image when a mobile phone camera shoots 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 point it at an LED light source. If your car has fluorescent lights, you can easily observe this strange phenomenon through the smart camera camera.

Flicker-free LED lights protect children’s vision

In fact, the LED light source flickers at a frequency that is imperceptible to the human eye. Car reviewers often encounter scenes that drive them crazy: when taking photos of a car, the car turns on the fluorescent lights, and the final shooting effect will make them very frustrated. This stroboscopic effect can be simply explained as the conflict between the two lights.

What is the stroboscopic effect? ​​

If you look through previous physics books, you will find that people often have a tendency, called "persistence of vision" phenomenon, where we can continue to perceive things even if they are no longer in front of us. We can see "persistent images" rather than a set of discrete static images.

The LED light source flickers at a high frequency that is imperceptible to the naked eye, so we see the lights on until we turn the power off completely. Likewise, video is actually a series of images captured in rapid succession in frames per second, and when we play games together, this continuous vision tricks our brains into seeing the events on the screen as one continuous fluid motion. :16px;color:#4E4D4D;font-family:"background-color:#FFFFFF;"> When the number of frames per second exceeds the frequency of the LED light source, the mobile phone camera shows an obvious flickering effect, which is the stroboscopic effect.

LED lights will flicker when switching rapidly on and off, and whether they flicker or not depends mainly on the nature of the current supplied to it. Typically, LED lights flicker at a frequency that is not directly noticeable to the human eye, so one can rest assured that any visible camera flicker is actually normal operation of the light, and the only thing that should be of concern is human blinking.

Action is a set of static shots that appear fluid to the human eye due to the persistence of our vision

DC power

When a DC power supply provides power to an LED light, the DC power supply here is usually a battery. The LED light diodes are always in a charged state, so they continuously release light energy and remain on until the circuit is disconnected. When a mobile phone camera captures an LED light powered by DC , the screen will flicker continuously.

AC power supply

AC is usually provided by a power source like a wall socket. Essentially, AC is turned on 2 times and off 3 times in one cycle, so the excited electrons consume all their energy in the form of light, return to the electron shell 3 times, and then are excited again. Therefore, an LED light connected directly to AC power will appear to flicker in the video.

However, it is not feasible to connect LED lights directly to AC power, which will cause the LED light life to be significantly reduced due to cycling of switching states. Therefore, they are connected to a regulator called a "driver", which converts AC to DC before wiring them to the light. LED lights running through the driver will not show flicker.

Pulse width modulation

With the continuous development of transmission technology, the flickering of mobile phone cameras caused by LED lights is not only entirely attributed to the AC or DC power supply. The LED lights powered by the driver will flicker. In order to reduce power consumption, the power supply can be bundled into discrete pulse currents, and Instead of continuous power, this is called pulse width modulation and is commonly used in automotive fluorescent lamps.

The coin cell is a direct current source that keeps the LED light on unless the circuit is disconnected

Can the strobe be stopped?

Stopping the strobe itself is very unhelpful, however, the irritating strobe effect is what we try to While eliminating the stroboscopic effect is an incredibly precise task, it is easily reduced by adjusting frame rate and shutter speed.

Outside the United States, alternating current is supplied at a frequency of 50 Hz, which means that the current changes between on and off 50 times in 1 second. The stroboscopic effect can be significantly reduced by adjusting the camera parameters, namely shutter speed and frame rate to multiples or fractions of 50.

Some LED lights are adjusted by the driver, and the flickering frequency is controlled by adjusting their switching period. If the flickering rate is adjusted to exceed the camera frame rate, the stroboscopic effect can be effectively eliminated.

Do incandescent light bulbs also flicker?

Like LED lights, incandescent bulbs switch on and off in alternating current, that is to say, in the off state, the filament in the incandescent bulb is not sufficiently cooled, which will not show a significant effect on the mobile phone camera. Therefore, it is impossible for us to see the incandescent bulb flickering on the mobile phone camera.