Why Do LED Lights Flicker On the Camera?
The “flicker effect” is a perceptible flickering effect that typically occurs when a phone is facing an LED light source for shooting.
Have you ever seen a phone camera flicker when capturing LED light sources, but it is normal when viewed directly with the naked eye? You can do a very simple experiment by turning on your phone camera and aiming it at an LED light source. If your car has fluorescent lights, this strange phenomenon can be easily observed through the smart camera camera.
In fact, the frequency of LED light source flickering is imperceptible to the human eye, and car review enthusiasts 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 flicker effect can be simply explained as the conflict between two types of lights.
What is the flicker effect?
If you flip through previous physics books, you will find that people often have a tendency known as the ‘visual persistence phenomenon’, where we can continuously perceive things even if they no longer appear in front of us, and we can see ‘continuous images’ instead of a set of discrete static images.
The LED light source flashes at high frequencies, which are imperceptible to the naked eye. Therefore, we see the light on until we completely turn off the power. Similarly, a video is actually a series of rapidly and continuously captured images, captured in frames per second. When we play games together, this persistent visual perception deceives our brain into seeing the events on the screen as a continuous fluid motion.
When the frame rate per second exceeds the frequency of the LED light source, the mobile phone camera exhibits a noticeable flicker effect, which is known as the strobe effect.
LED lights will flicker when quickly switching between on and off states, depending on the nature of the current supplied to them. Normally, LED lights flicker at a very high frequency, which is imperceptible to the human eye or invisible to the naked eye. Therefore, people can rest assured that any visible camera flicker is actually due to the normal operation of the light, and the only thing that should be of concern is human blinking. However, it is a very broad statement to say that LED lights always flash during operation.
DC power supply
When the DC power supply provides electrical energy to the LED light, it usually refers to the battery. The LED light diodes are always in a charged state, so they continuously release light energy and remain connected until the circuit is disconnected. When a mobile phone camera captures an LED light powered by direct current, the image will experience continuous flickering.
AC power supply
AC power is usually provided by power sources such as wall sockets. Essentially, AC power is turned on and off twice and three times in a cycle. Therefore, excited electrons consume all their energy in the form of light, return to the electronic casing three times, and are then excited again. Therefore, an LED light directly connected to an AC power source will flash in the video.
However, it is not feasible to directly connect LED lights to AC power sources, as this can significantly reduce the lifespan of LED lights due to the cyclic switching of switch states. Therefore, they are connected to a regulator called a “driver”, which converts AC power to DC power 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 flicker of mobile phone cameras caused by LED lights is not solely attributed to AC or DC power supply. LED lights powered by drivers will flicker. In order to reduce power consumption, the power supply can be bundled into discrete pulse current instead of continuous power supply, which is called pulse width modulation and is commonly used in automotive fluorescent lamps.
Can the flicker stop?
Stopping the flicker itself is very useless, however, the stimulating flicker effect is what we are trying to eliminate. Although eliminating the flicker effect is an incredible precision task, it can easily be reduced by adjusting the frame rate and shutter speed.
Except for the United States, alternating current is provided at a frequency of 50 hertz, which means that the current changes 50 times between on and off within 1 second. By adjusting camera parameters such as shutter speed and frame rate to multiples or fractions of 50, the flicker effect can be significantly reduced.
Some LED lights are regulated by drivers, and their flicker frequency is controlled by adjusting their switching period. If the flicker rate exceeds the camera frame rate, the flicker effect can be effectively eliminated.
Can incandescent light bulbs also flicker?
Like LED lights, incandescent bulbs switch on and off in alternating current, which means that in the off state, the filament in the incandescent bulb is not sufficiently cooled, which will not have a significant effect on mobile phone cameras. Therefore, we cannot see incandescent bulb flickering on mobile phone cameras.
