I tested this with vanilla XCOM1. In 7.9.16, visibility in dark and smoke was 5 regardless of whether you toggled personal light with 'L'. In 7.9.21, the visibility was now the same 5 tiles if you kept personal light enabled, but if you disabled it, you couldn't see past 2 tiles.
For what it's worth, I tested the same thing with an OXC version from 2021. There the visibility in dark and smoke was 5 tiles regardless of whether you disabled personal light or not.
On personal light:
I'm not sure how personal light actually affects the visibility of enemy units seeing you in the dark, or should it.
https://www.ufopaedia.org/index.php/Controls_(OpenXcom) describes this as 'L – Toggle Personal Lighting (light up the space around your soldiers to see them in dark terrain easier).' OXC lacked 'night vision mode' and ALT-press to help with this that OXCE has. So it appears that personal light in OXC was just an UI feature for playing experience, not something that would affect game mechanics in any manner. But at least now it does in OXCE. And that would require major documentation.
The default personal light in OXCE is 15. In my experience, XCF armors with personal light value '5' don't stand out in the dark and allow enemies to snipe at you. But if you take, for example, a tank which has the default personal light of 15, the enemies seem to start shooting at it even if they otherwise could not (and you can approach them more stealthily by disabling personal light).
If in OXCE 'personal light', even with its default settings of 15, is intended to affect game mechanics, in contrast to being an UI feature in OXC, it should be documented in cat-sized letters. And I doubt why repurposing OXC personal light UI feature to affect game mechanics would be a good idea.