240 watts of LED backlight for a 23″ computer monitor!

[This is a very old article from scanning backlight experiments in 2012]

A 23″ LCD computer monitor is 286mm high x 508mm wide. From math calculations on LED ribbons (120 LED per meter, 6mm wide, 6500K, ~10watt/meter, 80+CRI available), one can put 48 rows of 6mm-width ribbon segments behind a 23″ LCD. That’s a whopping 240 watts of backlight for a 23″ computer monitor!  

This will allow 90% motion blur reduction using ultra-short scanning backlight strobes (see FAQ) without a dim picture, 1.6ms strobes at 60Hz, resulting in 24 watt average actual power consumption. Many new 23″ LCD monitors with a LED backlight, adjusted to a comfortable brightness, consume just about 15-20 watts for the backlight itself. I will have brightness left over to go to 95% motion blur reduction, using 0.8ms strobes at 60Hz native refresh (simulating equivalence to 960Hz), or 0.4ms strobes at 120Hz native refresh (simulating equivalence to 1920Hz).

LED ribbons are cheap (search eBay, Alibaba, Google for “LED ribbon”). If you know another inexpensive alternatives of putting nearly 300 watt of backlight behind a 23″ monitor, contact mark[at]scanningbacklight.com


Prebuilt high-power switch for Arduino

Found a pre-made Arduino-compatible MOSFET switch for $18 each. Four of these 4-channel switches will be suitable for a 16-segment Arduino scanning backlight. These can switch well over 100 watts per segment, and at frequencies up to 200,000Hz; fast and powerful enough for an ultra-bright scanning backlight utilizing ultra-short strobes.

MOSFET power switch suitable for LED ribbons, to modulate backlight segments.

A similar MOSFET switch is being used to operate LED ribbon.


Arduino Photodiode Input Lag Tester

I have a breakthrough in a millisecond-accurate input lag tester, that is as almost as accurate as using as an oscilloscope and a photodiode. I am creating photographs on how you can construct your own inexpensive Arduino input lag meter. No soldering iron, no no Electronics 101 knowledge absolutely necessary. Just enough DIY skills to assemble hardware & compile a supplied program.

The Arduino photodiode scope (input lag meter/stroberate meter) will be indispensible for my continuing work on the scanning backlight. PC application will be provided. Watch this blog!

EDIT: See the Sneak Preview.


Benchmark electronics prototyping

The Arduino and initial components for prototyping have been purchased and assembled. The prototype circuit for an upcoming 16-segment scanning backlight is currently being tested with simple LED’s (LED ribbons will be used instead in the near future).

Arduino tests today have shown that very accurate 1/10,000th second strobes (per segment) can be accomplished. LED’s can switch in less than one microsecond.

Currently, the limiting factor is the amount of brightness that can be squeezed into a scanning backlight behind an LCD panel. Short periods of illumination for each segment results in a dimmer image. Extra backlight brightness is needed in order to compensate for the long dark periods between strobes (at 1 strobe per segment per LCD refresh). The design goal is at least 90% motion-blur reduction (suitable for games and computer, insignificant input lag) without using motion interpolation. This requires LED’s to be dark 90% of the time. As a result, the backlight needs to be 10 times brighter during the illumination, just to compensate for the short illumination strobe!

New posts added in threads at AVSFORUM, overclock.net, and hardforum.com.


Schematic diagram for scanning backlight

NOTE: This is a very old article.
Newer article is Electronics Hacking: Creating a Strobe Backlight.

This is a simplified schematic diagram for a home-made scanning backlight driven by an Arduino, an open-source electronics prototyping platform.The Arduino monitors the VSYNC signal (input-lag compensated) and executes a backlight scanning sequence, using ultra-short strobes of super bright LED’s per segment. This greatly reduces motion blur. For the brightness required for ultra-short strobes, reels of LED ribbons totalling thousands of LED’s will be used instead of individual LED’s.

Note: This is a draft diagram. It may be missing some supplemental components (e.g. resistors at MOSFET gates).

EDIT: This is a very old article. Please see Electronics Hacking: Creating a Strobe Backlight for current information.