Er? There were metric-f'tons of green-phosphor terminals in use "back in the day", and I don't recall anybody ever adjusting them to reduce brightess... I'm not even sure if most them were even
capable of easy adjustment.
E.g., the green model of the H19/Z19 (super popular), various IBM synchronous terminals (the ones I remember from the system/34 had a particularly saturated green phosphor), the later H29 (a very pleasant bright whitish-green), various cheapo Wyse models from the final days of dedicated terminals (though usually these were pretty adjustable), the original PC monochrome monitor (adjustable, but typically quite bright and saturated green), etc.
[Not that I actually like jwz's blog style, mind you...]