[Tagging] lit=yes/no threshold
gdt at lexort.com
Sun Jul 7 14:10:05 UTC 2019
Michael Patrick <geodesy99 at gmail.com> writes:
> You'd probably be okay using the 10 lux indicated by the Illuminating
> Engineering Society. But considering that the illuminate area is uneven ( a
> notion also covered in the standard ) and usually fairly extensive, and
> illumination measurement is a technical skill, and it is a moving target
> because of the daily cycle and weather, it probably isn't practical o
> expect some member of the general public to collect the data.
Agreed that most mappers cannot measure this, and that all mappers
cannot measure it easily.
About IES and 10 lux: in my town that is considered very high, and in
parking lots beyond what is allowed. A parking lot that ranges from 0.5
to 3 lux is considered lit. Average illuminances tend to be 3-4ish, if
built according to our light polllution bylaw. (I realize that typical
city notions of what is appropriate are different.)
So, saying that something under 10 lux is "lit=no" would not be ok.
I tend to leave the definition alone and not worry that people are
making judgements in marginal cases. If there are fixtures installed to
light something, and they are doing what was more or less intended, then
it's lit=yes, even if the level is lower than somebody else might like.
To me, marginal cases include:
there were lights installed but they are now not working well (but
somewhat). This is rare enough not to worry about.
on a walkway in the city, where there are no fixtures intended to
light the walkway, but due to ambient light from many nearby sources,
there is a level of 1 lux or more
This second case could arguably be lit=no but it's also dark=no.
I like the suggestion of needing to use a flashlight. I don't think we
should get too hung up on the edges of subjective. A notion might be
Do more than 50% of the users of the path either use a flashlight or
wish they had one to use.
which is of course fuzzy, but people making that judgement in good faith
are unlikely to have serious arguments. For cases right on the edge, it
doesn't really matter how they are tagged.
Beyond this, recording illuminance levels makes sense, even though
that's another can of worms.
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