Gas-Discharge Display Cells as Bidirectional Optical Sensors: A Full-Factorial Analysis of Readout Architecture, Ambient Light, and Visibility Range

Gas-discharge display cells have been proposed as bidirectional pixels that both emit and sense light. This article re-examines that proposal with a corrected physical model and an expanded full-factorial design of 966.7 million deterministic runs. The design spans emitter power, phosphor channel, photocathode quantum efficiency, photoelectron extraction, target distance, size and reflectance, pixel size, ambient irradiance, internal crosstalk, and two readout families: analog photocurrent and Geiger mode discharge. The optical return is the exact Lambertian disk expression, ambient background scales with pixel area and spectrum, synchronous detection is not credited with suppressing white shot noise, and reconstruction gain is represented as explicit pooling with its resolution cost. A variance decomposition shows that distance, target area, and integration time dominate the analog response, while emitted power explains under 5% of the variance. Geiger-mode readout is bounded by ceilings that no signal can lift: a gated cell is limited by background occupancy per gate, and a DC-biased cell by its dead time, which at the measured plasma panel sensor recovery of about 500 μs prevents detection at video rate. At laptop power in office light, a bialkali-coated cell read as an analog photocurrent on the blue channel detects a face at 0.77 m without pooling and 1.26 m with 50-fold pooling, while a gated Geiger cell reaches 0.37 m. These results correct an earlier tracking-matrix analysis, place the concept at technology readiness level 2, and define the bench experiment needed to advance it.