Nexus 7 (2013) Review: An Introduction to PWM Flicker

Despite three aging three years since its release, the Google Nexus 7 (2013) continues to be relevant as a well-performing tablet at a rock bottom price.  This tablet is still widely available for purchase new and second-hand at a reasonable cost.  The 2013 model can be distinguished from the 2012 model by the lack of silver-colored metal ridge around the circumference of the device.


Our measurements indicate the device uses pulse-width modulation (“PWM”) to modulate screen brightness.  PWM is a method in which power supplied to the backlight is cycled on and off at such a high frequency that it gives the illusion of steady light output.  To increase brightness the screen remains on for a longer period during each cycle.  To decrease brightness the screen is turned off for a longer period during each cycle.

For those not sensitive to flicker, PWM helps to maintain colour accuracy across the brightness range and also allows for a lower minimum brightness.

Unfortunately, those sensitive to flicker will likely find PWM to be the most problematic because it quite literally turns on and off rapidly switching between short periods of maximum brightness and being ‘off’.  To offset the negative impacts of PWM, some manufacturers use exceptionally high frequencies that are far less likely to cause adverse neurological effects.

In this case the Nexus 7 (2013) uses PWM.  Our measurements indicate the screen is cycled at a relatively high frequency of 965 Hz.  Flicker can be avoided entirely only if screen brightness is set to 100%.

Below is the screen output between 1% and 100% brightness at 10% intervals.

1% Brightness


10% Brightness


20% Brightness


30% Brightness


40% Brightness


50% Brightness


60% Brightness


70% Brightness


80% Brightness


90% Brightness


100% Brightness



Coming soon.


Coming soon.


Light is actually photons traveling in the shape of waves, but unlike waves in an ocean photons can oscillate in all directions.  Polarized glasses typically only allow passage of photons through the lenses if the photons oscillate vertically.  The further the orientation of the photons deviates from vertical, the less chance the photon will be able to pass through polarized lenses.

While natural light consists of photons oscillating in all orientations, photons emitted from electronics typically have only a single orientation.  Therefore, for those reliant on polarized glasses it’s important to consider whether the device screen will be visible when wearing polarized glasses.

For the Nexus 7 (2013) light output is oriented vertically from the portrait position.  Using this tablet in portrait mode will permit maximum light throughput but unfortunately using the tablet in landscape is not feasible.



The Nexus 7 (2013) uses harsh PWM flicker to module light output but does so at a high frequency of 965Hz therefore offsetting the negative impact on viewers.  While PWM can only be avoided at 100% brightness, it results in an exceptionally bright screen and not feasible for those sensitive to light.  Furthermore the device is limited to portrait when used in conjunction with polarized sunglasses.


  • Great device for those not sensitive
  • The relatively high flicker frequency of 965Hz is likely to offset some of the negative impacts of utilizing flicker in this screen


  • Screen uses PWM flicker to modulate brightness
  • Screen not visible through polarized glasses while in landscape

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