I have a susceptibility to monitors that use Pulse Width Modulation (PWM) to vary brightness. What happens is that when I use a device with a PWM display at certain frequencies, I end up with double vision after about 5 minutes. It takes just a couple of minutes for that to go away, but in the long term, I don’t think it can be a good thing.

What is PWM?

PWM, or pulse-width modulation, is used in some computer display units as a method of turning down the brightness of the display. Instead of reducing the current to the backlight, on LED backlights, you can vary the cycle of how long the poewr is applied. For instance, if you turn an LED on and off  250 times per second, with the LED being on 50% of the time and off 50% of the time, the display will be at 50% brightness. It is an effective way to dim a screen without color temperature shifts.

The Problem with PWM

Some people are susceptible to the frequency of the backlight. I am. I have noticed this problem with my older G2 cell phone, as well as the older iPad 1 and my current Galaxy S3 phone. I have not noticed a problem with my Dell Latitude laptop, nor the iPad 2. The problem that I have is that after 5 minutes of Angry Birds Star Wars on my Galaxy S3, my vision starts doubling up horizontally. I’m not sure why PWM affects me like this, but there seems to be a percentage of the population that is affected by this.

I did a test on my S3 to find out the backlight frequency. It runs at about 250hz.

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