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Hi Michael,
Yes, I have seen some optical effects in those glass beads as well! Maybe
not the actual "glass-bow" though, but they may be worth mentioning:
I've noticed the heiligenschein (the equivalent of wet heiligenschein,
that
is) in traffic signs when the sun is low and the sign is near the
antisolar
point. I have also seen something similar to your observation, rainbow
colors, but in these road signs (not marks *on* the road). The rainbow
colors I saw reminded me of antisolar iridescence. Maybe it was actually
a
"rainbow" or glassbow for that matter. I would typically see these colors
in the blue-white road signs over the highways in Holland, when the sun
would be low in the back and the sign forward overhead or to the side
(i.e.
not exactly near 180 degrees opposite the sun). Closer inspection learned
that the trafic signs are composed of the same kind of retro-reflecting
glass beads as the road marks. That way they are always easy to see from
your car, since you are on the light source itself.
Speaking of antisolar iridescence: I haven't seen this term, or photos, in
any optics book yet. Why is that? Antisolar iridescence is as natural an
effect as the common iridescence, but it would (I guess) be caused by
spurious glory rings instead of the corona. Anyway, after figuring out
that it might occur, I have seen the antisolar iridescence several times
in
the mountain wave clouds here in New Mexico and also have a number of
pictures of the phenomenon that I still need to scan in. It's one of
those
phenomena that go unnoticed unless you expect it and know where and when
to
look. I've seen it up to 20 degrees off the antisolar point, as slight
green and pink pastel colors in the bases of lenticular clouds. The
colors
are even more pastel than regular iridescence. It's really obvious to see
from an airplane, looking away from the glory. If anyone is interested I
can maybe find and scan the photos tomorrow.
Harald
At 20:01 2003-06-14 -0700, you wrote:
>Hello Listees,
>
> Ever heard of seeing optic effects form in raod
>paint? well I was on vacation in the smokey
>mountains and up near Clingman's Dome there was a
>paint truck repainting the edge lines and to make
>the paint more reflective and easy to see when a
>car's headlight hits tiny glass beads are used
>well my brother was the first to see it and I had
>my camera and I saw it too!!! and the bow was
>being generated by the tiny glass beads in the
>paint!!! The bow had a much smaller radius than a
>standard rainbow from water drops because the
>refractive index of glass is higher and the bow's
>radius is 28 degrees.
>
>If any of you are interested heres some pics to
>look at, I am not sure if anyone has seen this
>but this was really cool.
>
>Best,
>Michael
>
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