You'll find that measurements made in dim light are more repeatable and
consistent, but normally the average endpoints are about the same.

Bright light and small pupils introduce greater depth-of-field and that
increases variability. Dim light, large pupils and small depth-of-field make
small changes more obvious.

Normally there won't be much difference between bright and dim refractions.
One exception is in early cataract, where the crystalline lens becomes less
homogeneous and its center may have a different index of refraction than the
periphery. This can lead to different refractions in bright vs. dim light.

-MT

Dear Ron,
Subject:  Visual Acuity in room illumination
and deep dusk.
I am not certain of the intent of your question, but illuminatino can
make the difference between on prescription lens -- or a -2.0 diopter
lens.
One man "Mike" was working to clear his vision from -2.75 diopters.
(He went from -1.5 to -2.75 in four years.)
When he quit "cold turkey" he found he could read the 20/50 to 20/70
line.
After work with a plus, he found he could read the 20/40 line (which
passes the DMV requirement.)
He parents insisted he go back for a MEDICAL exam.  This exam cleared
him of all medical problems.  But the lens necessary to clear his
vision (in dusk conditions) was -2.0 diopters.
He went back and checked his own eye chart, still at 20/40.  Why the
difference?
Further, he then "borrowed" a -1.25 diopter lens and found that he
could clear his
room-illumination chart to 20/20.
So there is a serious difference in the "prescription" you will receive
-- depending on chart illuminaion level.

Best,

Otis
Engineer