In article ,
(Phillip Gabero) writes:
Let's say
- there was a habitable planet around Alpha Centauri-A
....
- B is at opposition, getting the planet as close as 10 AU to B
[and ignoring A]

At 10 AU Alpha Centauri-B's apparent magnitude is -20,9,
which makes it 223 times dimmer than our sun.

My question now is what are the light levels like at that
time?

I haven't checked your apparent magnitude value, but it looks
plausible.

You have pretty much answered your own question: the illumination
levels are like those at a 99.6% partial solar eclipse. That is
indistinguishable by eye from the 99% eclipse you observed, though of
course a camera exposure meter could tell the difference (about 1
f-stop). Shadows would be about 10 times sharper than normal solar
shadows, similar to (but not as sharp as) those at the partial
eclipse. Color vision should be near normal, and reading should be
very easy. (Isn't this brightness level about 1000 times that of the
full moon?)

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