Figure and field are different hues at the same brightness, so there is no edge for the luminance channel to find. The word does not vanish — it goes soft, floats, and refuses to hold still, because you are reading it with the part of your vision that is bad at reading. Switch to Luminance only for the proof that the edge was never there. Calibrate first: isoluminance is a property of your screen and your eye, not of the file.
Up to ten characters. Short and fat wins: the chromatic channel resolves maybe a tenth of what the luminance channel does, so a thin glyph is a glyph nobody will ever read.
Noise is per-dot luminance jitter, applied to figure and field alike. It is uncorrelated with the message, so it cannot leak it — and it hides whatever calibration error is left.
Fine stripes of the two hues. Slide until the boundary between them is least distinct — the stripes will look like they are shimmering or dissolving rather than showing crisp edges. That setting is your isoluminant point on this display.
Uncalibrated — using sRGB's population average