The vast majority of modern televisions screens flicker, and the level of pulsation is 100% (the screen goes out and lights up). This can lead to eye strain, headaches and exacerbation of nervous diseases.
If you look through the camera of the phone at the rows of TVs in the store, most likely their screens will burn exactly and no pulsation in the form of strips running across the screen will be visible. The fact is that in stores the intensity of the backlight of all TVs is always set at 100%. At home it turns out to be too bright and the intensity of the backlight has to be reduced. And then there is a ripple.
In the video, slow 40 times (shooting 1200 fps) LG 32LH570U TV screens (left) and Sony KDL-32RE303 (right) with 30% backlight look like this:
With the help of the device
Uprtek MK350D, I measured the level of pulsation of the screens of nineteen TVs in three stores. When measuring, the backlight level was set to 50% and a white field was displayed on the screen.
The measurement results are disappointing. 100% backlight ripple found on the following TVs:
Toshiba 32L5650VN
LG 32LJ510U
LG 32LH570U
LG 32LJ600U
LG 32LJ610V
LG 32LK6190PLA
LG 43LJ510V
LG 43LJ610V
Samsung UE32J4710AKXRU
Samsung UE40MU6103U
Philips 32PHS5302 / 60
At the Hisense H32A5600 TV, the device showed a ripple level of 36%, at the LG 49SJ810U TV - 89%.
All tested Sony TVs ripple less than 5%:
Sony 32RE303 - 1.6%
Sony 32RE403B - 1.3%
Sony 32WD752S - 1.1%
Sony 32WD756BR - 1%
To my surprise, the ripple was completely absent from the cheap Chinese TVs Haier LE32B8500T and Haier LE39B8550T, but it turned out that they simply do not physically have to adjust the brightness of the backlight, which always burns at full power.
Where does pulsation come from? The light source in the LCD screens of modern TVs are white LEDs. When the backlight brightness is set to 100% and the eco modes are off, the LEDs are powered by constant voltage and there is no ripple. Brightness adjustment is done using PWM (pulse width modulation) - usually the LEDs are turned on and off 100 times per second. When they burn 50% of the time, and 50% of the time off, the brightness is 50%. If one tenth of the total time is lit, 10% is obtained.
It is important to understand that the PWM frequency has nothing to do with the refresh rate of the TV screen, which is often indicated in the specifications. The type of matrix and the location of the LEDs are also not related to the ripple of the backlight.
The higher the PWM frequency, the less noticeable the pulsation, but scientists believe that even high-frequency pulsations affect the brain, which are not visible visually.
Of all the tested TVs, one showed up - Hisense H32A5600, whose PWM frequency is 200 Hz, not 100. On the slow-motion video, you can clearly see the difference.
Hisense H32A5600
LG 32LJ610V
That is why the device, designed for pulsation with a frequency of 100 Hz, showed 36%. In fact, the level of pulsation in Hisense H32A5600 is the same 100% (the screen goes out completely).
A very interesting phenomenon was discovered when testing a rather expensive LG 49SJ810U TV, in which the device showed a ripple level of 89%. On the screen with a periodicity of 100 Hz are blackout waves. Apparently, this is done to improve the smoothness of movement.
You can see how dark waves are running across the screen of the TV, and the TV next to it just blinks PWM.
In fact, there are no technical problems in adjusting the brightness of LEDs without PWM, simply by changing the current of their power. Apparently, SONY has done just that. Alas, the manufacturers of the rest of the TVs for some reason continue to use PWM.
By the way, there is even a video on Youtube, where the amateur radio operator explains how to remake the TV's backlight control unit to get rid of the pulsations.
Check for visible ripple on your TV screen is easy. Reduce the backlight level to the minimum (just the level of the backlight, not the brightness!). Twist the pencil in front of the screen (see the
pencil test ). If there is no strobe effect and you see a blurred image of a pencil, there is no visible ripple (either it does not exist at all or the PWM frequency is above 300 Hz). If you see a stroboscopic effect - the pencil “breaks up” into many pencils, alas, pulsation is available.
The only way to get rid of the ripple of the LCD TV screen without altering it is to turn off all eco-modes, set the backlight level to 100% and lower the brightness to achieve a comfortable picture. The black color will most likely turn gray and the picture will be more faded, but there will be no pulsation and the eyes will be less tired.
© 2018, Alexey Nadyozhin