80/90 headlights, what do you think?

[Phil@isham-research.demon.co.uk (Phil Payne)]

In message <199710040904.JAA225936@out2.ibm.net> "Bruce Bell" writes:

> Yes, that is what I meant. :-)  I was thinking of the inverse distance
> squared relationship and I should know by now not to take verbal shortcuts
> on this list. Gee, If I'd just used the word "perceived" or
> "effective".........

The absolute luminosity of an object is independent of its distance from
the observer.

True - the inverse square law results in only a quarter as much light
reaching you if it's twice as far away - but the area of the image on
your retina is also only a quarter of the size, and it cancels out.

Light per unit area of image remains the same.  The greatest loss is
in visual contrast because air is not completely transparent and
reflects a lot of stray light back to the observer.

--
 Phil Payne
 phil@isham-research.demon.co.uk
 Phone: +44 385302803  Fax: +44 1536723021  CIS: 100012,1660