"Greg Farris" wrote in message news:dvpchc$15e1

Are you guessing then?

Not really -- just estimating (based on 35 years worth of looking) because I
don't know the exact specification. You can bet that somewhere there is an
FAA spec telling manufacturers *precisely* the number of lumens, the
candlepower, and the distance from which the light must be visible under
specified circumstances of visibility.

......but many other situations where it is not at all clear
from these light which way a plane is going. This applies to airliners as
well, whose position lights often seem scarcely larger or brighter than
those
of light aircraft. Few airliners have a really clear, white light in the
back
to indicate they are moving away from you .......

You don't necessarily need to see the white light to make that call. That's
precisely why the specs call for different types of lights in stipulated
locations -- different colors, some steady, some flashing -- so you won't
have to see all the lights to make a determination.