screen brightness communicator

unlike the optical modem’s pure black-and-white flashes, this tool modulates a midtone background. the change is small enough to feel ambient yet still readable to a camera. great for boardroom-friendly demos and for showing how subtle li-fi can be.

118 symbols · ~17.7 s per loop

lower values are stealthier but require darker rooms or shorter distances · 25–35% works well in office light

• brightness modulation is hard to notice but easy to detect. cameras average across many pixels and many frames, so even a 10–20% swing reads as a clean square wave.
• this is the principle behind subtitled li-fi: a rectangle in the corner of a screen can carry a stream of text invisible to a viewer, decoded only by a paired camera.
• the channel works through reflections too. you can sometimes decode a transmitting display by pointing the camera at the wall it’s lighting up.