Led Knowledge--why the LED lights flicker on cameras

The”stroboscopic effect”is a perceptible flickering effect that usually occurs when use mobile phone shooting Led Light source.

Have you ever seen the mobile phone camera flickering when shooting Led Light source,but it is normal when viewed directly by eyes?You can make one simple experiment,turn on mobile phone camera and focus on the LED source,if your car has fluorescent lights then this strange phenomenon can by easily observed through the smart mobile phone camera.

Flicker-free Led Lighting can protect eyesight for Children

In fact, The frequency of Led Light source flickering cannot be perceived by Human eyes. The car review enthusiasts often encounter some crazy scenes:when shooting, car turn on fluorescent lights, and the final effect will make them feel frustrated. This “stroboscopic effect”can be simply explained as the conflict between two lights.

If you read the previous physics books, will find that people have one tendency known as “Persistence of vision”.Where we continue to perceive things even they’re no longer  appear,and we can see “persistent images”rather than a set of discrete static images.

The high frequency of Led Light source flicker can not be perceived by human eyes,so we only see the lights is turn on until the power off completely. Similarly, video is a series of images captured in rapid succession at frames per second.When play games together, this persistence of vision tricks our brain into perceiving the events on screen as one continuous fluid motion.

When the number of frames per second exceeds the frequency of the Led Light source,the mobile phone camera will show one noticeable flickering effect which is “Stroboscopic effect”.

The Led Lights will flicker when they switch between on and off states quickly, depending on the nature of the current supplied to it. Generally, the frequency of Led Lights flicker too high to be perceived directly by eyes, or invisible to eyes. Therefore, one can rest assured that any visible camera flicker is the lights working normally, the only thing that should be a concern is eyes blinking. However, said an Led Light is always flickering when in working is one broad statement.

Action is a set of static shots that appear fluid to eyes due to our persistence of vision.

DC power

When DC power is providing power for Led Light, which is usually a battery, the Led Light diodes are always charged so they continuously release light energy and remain on until the circuit is disconnected. When phone camera shoots an Led Light powered by direct current, the image will flicker continuously.

 AC power

AC power is usually provided by a power source such as a wall socket.Essentially AC power is turn on 2 times and turn off 3 times in one cycle, so the excited electrons consume all their energy in the form of light,return to the electron housing 3 times, and then are excited again. Therefore the Led Light connected to AC power directly will flicker in the video.

However,it is infeasible to connect Led Lights to AC power directly, which will cause Led Lights life to be significantly reduced due to the on-off state cycling. So they are connected to one regulator called “driver”,which converts the AC power to DC power before wiring them to the lights. Led Lights working through driver will not show flicker. 

Pulse width modulation

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

The button battery is a DC power source that keep the LED on unless the circuit is disconnected

Stopping flicker in itself is extremely unhelpful,however the irritating stroboscopic effect is what we are trying to eliminate, and while eliminate the stroboscopic effect is an incredibly precise task,it it easily reduced by adjusting the frame rate and shutter speed.

Except for USA, AC power is supplied at a frequency of 50 Hz, which mean that the current turn on and off 50 times in one second.The stroboscopic effect can be significantly reduced by adjusting the camera parameters, setting shutter speed and frame rate to multiples or fractions of 50.

Some LED lights are regulated by drivers, which control the frequency of flicker by adjusting the turn on and off cycles. If its flicker rate is adjusted to exceed the camera frame rate that the stroboscopic effect can be effectively eliminated.