> LED back light screens flicker research

  • Posted on: 4 November 2015
  • By: tihomiry

Most of the modern LED backlight screens including Laptops, TV and smart phones use PAM technique for Pulse-amplitude modulation. This means that they switch on and off state very rapidly.
This is implemented to save energy and control the back light brightness, but it is harmful to the human nervous system and case eye strain.
I have tested some devices with photographic method by taking a shot of 1/8000 of the second. Each on and off transit state will produce a dark line in the shot. On the picture below is Samsung galaxy s3 that has a very poor performance. You can measure the on/off state frequency by counting the dark lines. A good display should has no lines on the shot. This will produce the comfortable frequency of above 4000Hz.

The flicker increase by reducing the screen brittleness. But using appropriate screen birthrates is important for eye comfort when staying at night in front of the computer.
You can easily test if your screen is good with a pen. Wave the pan in front of the screen. If you see a blued image, it is ok. If you see a scattered image then the flicker frequency is too low and your eye could see it.
If you have already such a bad device, you can use a software to reduce the brittleness that will actually twerk thee tone instead of the display back light. Such is Twilight for smartphone or flux for PC. Those apps also can make the screen warmer as the violet-blue light is most harmful for the eye. For Win 10 and latest Mac OS there is also embalmed functionality to make the screen tone warmer.

Here is my Samsung Galaxy S3 screen with 1/8000 of a second exposure:


You could read an interesting article in Bulgarian:


Witch is better. Stack or long exposure? It depends…

NGC 7000, South America nebula in Cygnus, taken by me from NAO Rozhen. 2 shots composed by 45 frames @ 30s, ISO 51200 with SW 200pds and Pentax k-5. Same processing with DeepSky Stacker and LightRoom.

To check the polar alignment of your telescope look trough the polar scope. When turning the Ra axis the polar star should move in the exact circle in the eyepiece without any deviation.

Removing the DSLR build in IR-cut filter will give you at least 50% more sensitivity for hydrogen alpha emissions of the nebulas. Also the camera will be more light sensitive at dark allowing you to shoot more faint objects.

We can check what is like to process day shot with similar to astrophotography techniques. It is cloudy in Bulgaria for the next week or so and I took shots of the nearby mountain trough the fog with 200mm lens.